JP2011029381A - Semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the carrier lifetime in a saturable absorption region and thereby attain superior self-oscillation characteristics (that is, to readily cause self oscillations), in a separated electrode type semiconductor laser element. <P>SOLUTION: In the semiconductor laser element, at least an n-type semiconductor layer, an active layer and a p-type semiconductor layer are laminated on a substrate. The semiconductor laser element includes an n-side electrode contacting with the n-type semiconductor layer or the substrate, a p-side electrode contacting with the p-type semiconductor layer or the substrate and a resonator. At least either of the p-side electrode or the n-side electrode is electrically divided into two or more regions by a dividing region crossing with the longitudinal direction of the resonator. At least in a part of the active layer, a second internal electric field that is a different kind from a first internal electric field is generated, in a direction identical to the direction of the first internal electric field by a p-n junction between the n-type semiconductor layer and the p-type semiconductor layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device in which electrodes are electrically separated into two or more regions by divided regions intersecting with the longitudinal direction of a resonator.

  Semiconductor laser elements are currently widely used, for example, for optical disks with a large storage capacity, more specifically for light sources for reading and writing BDs (Blu-ray Disks).

  However, in reading and writing of BD using a semiconductor laser element as a light source, the return light noise from the disk surface to the semiconductor laser element is the same as in the conventional optical disk apparatus such as CD (Compact Disk) and DVD (Digital Versatile Disk). Is a problem.

  As countermeasures against such return light noise, there are conventionally two methods: a method using high-frequency superposition for modulating the drive current and a method using self-excited oscillation characteristics in which the semiconductor laser element itself varies its output. is there. In either method, the noise characteristics are improved by reducing the coherence in a multimode oscillation state.

  Comparing the method using high-frequency superposition with the method using self-excited oscillation characteristics, the latter method, which does not require the incorporation of a high-frequency circuit in the system, is advantageous because it can realize cost reduction and downsizing of the semiconductor laser device. It is said that. However, in BD using a semiconductor laser element, only a method using high-frequency superimposition has been realized at present, and a method using a self-excited oscillation type laser element utilizing self-excited oscillation characteristics has not yet been put into practical use. Is in a situation that is not.

  In order to enable the use of a self-excited oscillation type laser element, it is necessary to form a saturable absorption region inside the semiconductor laser element, but it can be divided into three types depending on the formation method.

  The first type is a type in which a layer having a saturable absorption function is provided above and / or below the active layer (“saturable absorption layer formation type”).

  The second type is a semiconductor laser device having a stripe structure, in which the lateral refractive index difference (Δn) is reduced to weaken light confinement in the active layer, and the lateral light distribution is broadened with respect to the current distribution. In this type, the laterally neighboring region of the gain region (the active layer outside the stripe portion) is used as a saturable absorbing region (“Δn adjustment type”).

  In the third type, a current non-injection region in which no current is injected by separating the electrode into two or more regions is provided in a part of the longitudinal direction of the resonator, and this current non-injection region is used as a saturable absorption region. Type ("separation electrode type").

  Among these three types, the separation electrode type has an advantage that it can be manufactured by a relatively easy process without changing the structure of the semiconductor layer from a semiconductor laser element that has been put into practical use. Japanese Patent Laying-Open No. 2004-186678 (Patent Document 1) discloses a p-side electrode and an n-side electrode corresponding to a current non-injection region functioning as a saturable absorption region in such a separated electrode type nitride semiconductor laser device. It is disclosed that self-oscillation can be obtained by electrically short-circuiting and applying a reverse bias to the pn junction. Japanese Patent Laying-Open No. 2007-081196 (Patent Document 2) discloses a technique in which a current non-injection region is used for detection of laser light generated in a gain region.

JP 2004-186678 A JP 2007-081196 A

  In order to obtain the self-excited oscillation characteristic, the carrier life needs to be sufficiently short in the saturable absorption region with respect to the gain region. The short circuit between the p-side electrode and the n-side electrode located in the saturable absorption region or the application of a reverse bias to the pn junction in the saturable absorption region is caused by the internal state generated in the semiconductor layer. By using an electric field, the carrier lifetime can be shortened by sweeping out carriers generated by light absorption in the saturable absorption region from the active layer.

  In this case, applying the reverse bias increases the internal electric field generated in the depletion layer and expands the depletion layer region, so that the carrier life can be surely shortened. However, in order to put a semiconductor laser element having self-excited oscillation characteristics into practical use as a BD light source, it is necessary to newly provide a mechanism for applying a reverse bias, which is not desirable from the viewpoint of simplification and miniaturization of the system. Therefore, for practical use, it is considered necessary to obtain effective self-excited oscillation characteristics only by short-circuiting the p-side electrode and the n-side electrode.

  In this regard, Patent Document 1 states that since a nitride semiconductor has a larger band cap than a GaAs system, an internal electric field is increased, which is advantageous for shortening the carrier life. However, in order to obtain self-excited oscillation characteristics that can be put into practical use only by a short circuit between the p-side electrode and the n-side electrode, it is necessary to further shorten the carrier life. For example, in order to exhibit self-oscillation characteristics over a wide temperature range, or to maintain self-oscillation characteristics even after long-term use, the carrier life is shortened and the tolerance for self-oscillation characteristics is increased. It is effective.

  On the other hand, the self-oscillation type semiconductor laser device has a drawback that a sharp rise of the optical output occurs in the vicinity of the threshold current. If the excitation oscillation characteristic is shown, it may be effective for such a problem.

  Patent Document 2 discloses a technique that uses a current non-injection region for detection of a laser beam generated in a gain region. As a current used for detection in this technology, a carrier generated by light absorption is used. The photo-induced current generated when sweeping out from the active layer is used. As described above, shortening the carrier lifetime for the purpose of self-excited oscillation characteristics also leads to an increase in the photoinduced current, and can therefore be used in laser light detection technology. The increase of the photo-induced current has advantages such as an improvement in accuracy when detecting the laser beam and an increase in tolerance of the bias voltage applied to the current non-injection region.

  Therefore, an object of the present invention is to shorten the carrier life of the saturable absorption region in a separation electrode type semiconductor laser element, thereby obtaining good self-oscillation characteristics (that is, easy self-oscillation). It is in.

  In the semiconductor laser device of the present invention, at least an n-type semiconductor layer, an active layer, and a p-type semiconductor layer are stacked on a substrate, an n-side electrode that contacts the n-type semiconductor layer or the substrate, and the p-type semiconductor layer. A p-side electrode in contact with the semiconductor layer or the substrate; and a resonator, wherein at least one of the p-side electrode and the n-side electrode is electrically separated by a divided region intersecting with a longitudinal direction of the resonator. The active layer is separated into two or more regions, and at least a part of the active layer has the first direction in the same direction as the direction of the first internal electric field due to the pn junction between the n-type semiconductor layer and the p-type semiconductor layer. A second internal electric field different from the internal electric field is generated.

  The active layer has a quantum well structure or a multiple quantum well structure having one or a plurality of well layers and one or a plurality of barrier layers. In the well layer, the n-type semiconductor layer and the p-type semiconductor layer are formed. A structure in which a second internal electric field different from the first internal electric field is generated in the same direction as the direction of the first internal electric field by the pn junction with the type semiconductor layer is preferable.

  Here, the second internal electric field is preferably a piezo electric field due to lattice distortion. The active layer is made of a nitride semiconductor crystal having a wurtzite crystal structure, and the n-type semiconductor layer is formed in the [000 + 1] direction of the active layer (in the present invention, the [0001] direction is The p-type semiconductor layer is preferably located in the [000-1] direction of the active layer.

  The n-type semiconductor layer and the p-type semiconductor layer are preferably nitride semiconductor layers, and the nitride semiconductor layers are each composed of a nitride semiconductor crystal having a wurtzite crystal structure. It is preferable.

  The substrate is preferably a nitride semiconductor crystal, and the nitride semiconductor crystal preferably has a wurtzite crystal structure, and is preferably GaN.

  The active layer is preferably InGaN that has undergone compressive strain. Moreover, it is preferable that the upper surface of the active layer is a (000-1) plane, and the p-type semiconductor layer is located in the [000-1] direction of the active layer. The upper surface of the active layer is a (000 + 1) plane (in the present invention, the (0001) plane is also referred to as the (000 + 1) plane in this invention), and the p-type semiconductor layer is the [ [000-1] direction.

  The n-type semiconductor layer and the p-type semiconductor layer preferably have the same crystal orientation as the active layer, respectively, and the substrate preferably has the same crystal orientation as the active layer. .

  The semiconductor laser device of the present invention preferably has a self-excited oscillation characteristic, and at least one region electrode separated by the divided region is short-circuited with an electrode opposite to the electrode. It is preferable that at least one region electrode other than the short-circuited electrode forms a non-short-circuit region that is not short-circuited with an electrode on the opposite side of the electrode.

  The present invention also relates to an optical disc apparatus using the semiconductor laser element as a light source, and also relates to an image display apparatus using the semiconductor laser element.

  Since the semiconductor laser device of the present invention has the above-described configuration, the carrier life of the saturable absorption region is shortened, thereby obtaining good self-oscillation characteristics (ie, easy self-oscillation). ).

It is a typical sectional view of a ridge structure central part showing one embodiment of a semiconductor laser device of the present invention. It is a typical sectional view parallel to the end face showing one embodiment of a semiconductor laser device of the present invention. It is a typical top view by the side of the p side which shows one Embodiment of the semiconductor laser element of this invention. 2 is a crystal structure diagram schematically showing a crystal structure of a nitride semiconductor. FIG. It is a band structure figure which shows the difference between the direction of a piezoelectric field and the direction of the internal electric field by a pn junction, and the relationship with a band structure. FIG. 3 is a schematic cross-sectional view parallel to an end face showing an embodiment different from FIG. 2 of the semiconductor laser device of the present invention. It is the expanded sectional view which expanded the active layer periphery of FIG. It is the top view which showed an example of the pad electrode pattern of the semiconductor laser element of this invention. It is a band figure of the active layer vicinity of the semiconductor laser element of an Example. It is a band figure of the active layer vicinity of the semiconductor laser element of a comparative example. It is typical sectional drawing parallel to the end surface which shows embodiment different from FIG. 2 and FIG. 6 of the semiconductor laser element of this invention. FIG. 10 is a band diagram in the vicinity of an active layer of a semiconductor laser device of an embodiment different from FIG. 9. FIG. 12 is a schematic cross-sectional view parallel to an end surface showing an embodiment different from those of FIGS. 2, 6 and 11 of the semiconductor laser device of the present invention. It is the expanded sectional view which expanded the active layer periphery of FIG.

  Hereinafter, the present invention will be described in more detail. In the following description of the embodiments, the description is made with reference to the drawings. In the drawings of the present specification, the same reference numerals denote the same or corresponding parts. In the present invention, the “upper surface” indicates a side where a semiconductor layer is formed in the substrate, and indicates a side farther from the substrate in each semiconductor layer.

  Further, in the following description of the embodiments, a description will be given focusing on a nitride semiconductor laser element using a nitride semiconductor crystal as a substrate and a nitride semiconductor layer as a semiconductor layer. It is not limited to such a nitride semiconductor laser element.

<Semiconductor laser element>
FIG. 1 is a cross-sectional view schematically showing an embodiment of a nitride semiconductor laser element 100 as an example of the semiconductor laser element of the present invention. That is, FIG. 1 is a cross-sectional view parallel to the longitudinal direction of the resonator at the center of the ridge structure of the nitride semiconductor laser device 100. On the other hand, FIG. 2 is also a cross-sectional view schematically showing an embodiment of a nitride semiconductor laser element which is a semiconductor laser element of the present invention, but is a cross-sectional view parallel to the end face of the nitride semiconductor laser element. FIG. 2 is a cross-sectional view in a direction orthogonal to the cross-sectional view of FIG. 1. On the other hand, FIG. 3 is a schematic plan view on the p-side electrode side showing an embodiment of a nitride semiconductor laser element which is a semiconductor laser element of the present invention. That is, FIG. 3 is a top view when the p-side electrode side of the nitride semiconductor laser element is directed upward.

  The nitride semiconductor laser device 100 of the present invention as shown in FIGS. 1 to 3 includes an n-type nitride semiconductor layer 20 which is at least an n-type semiconductor layer, and an active layer on a substrate 10 made of n-type GaN or the like. The layer 30 and the p-type nitride semiconductor layer 40 which is a p-type semiconductor layer are stacked in this order. However, the stacking order is not limited to this. For example, as shown in FIG. 11, on the substrate 10, at least a p-type nitride semiconductor layer 40 that is a p-type semiconductor layer, an active layer 30, The n-type nitride semiconductor layer 20 which is an n-type semiconductor layer may be stacked in this order. Thus, in the present invention, as long as at least the n-type semiconductor layer, the active layer, and the p-type semiconductor layer are stacked on the substrate, the order of stacking the semiconductor layers is not particularly limited.

  In the present invention, the substrate 10 is preferably a nitride semiconductor crystal, more preferably a wurtzite crystal structure, and more preferably GaN (particularly GaN having a wurtzite crystal structure). preferable. This is because the crystallinity of each semiconductor layer formed thereon can be improved, and a second internal electric field described later can be easily generated in the active layer.

  It is preferable that the upper surface of such a substrate 10, that is, the surface on which the semiconductor layer is laminated is a (000-1) plane. This is because the upper surface of the active layer can be easily set to the (000-1) plane without impairing the crystallinity, whereby the second internal electric field can be generated in the intended direction described later.

  The n-type semiconductor layer and the p-type semiconductor layer are each preferably a nitride semiconductor layer, and the nitride semiconductor is preferably composed of a nitride semiconductor crystal having a wurtzite crystal structure. The active layer is preferably composed of a nitride semiconductor crystal having a wurtzite crystal structure. More preferably, the n-type semiconductor layer, the active layer, and the p-type semiconductor layer are all composed of a nitride semiconductor crystal having a wurtzite crystal structure, and when the substrate is GaN, the crystal orientation is the same as that of GaN. In any case, the upper surface is preferably a (000-1) plane. Thus, the lower surface of each layer is preferably (000 + 1). Note that the notation on the left side of FIG. 2 schematically represents this. The reason why these crystal structures and crystal orientations are preferable will be described later.

  In FIG. 1 and FIG. 2, an n-side electrode 80 is formed on the back surface of the substrate 10 in contact with the substrate 10, but the n-side electrode 80 can also be formed in contact with the n-type semiconductor layer. . On the other hand, the p-side electrode 70 is formed in contact with the p-type nitride semiconductor layer 40 which is a p-type semiconductor layer.

  The semiconductor laser device of the present invention has a ridge stripe structure from which a part of the semiconductor layer (p-type nitride semiconductor layer 40 in FIG. 2) is removed (also simply referred to as “ridge structure” in the present invention). It is preferable. In this case, an insulating film 60 is formed in a region other than the ridge stripe portion 55 (that is, a side surface portion of the ridge stripe portion 55 and a planar portion following the side surface portion), and a surface portion (upper surface portion) of the ridge stripe portion 55 is formed. Only the current is injected. Therefore, a region having a width substantially equal to the width of the surface portion of the ridge stripe portion 55 in FIG. 2 and extending in the longitudinal direction around the active layer 30 acts as the resonator 90. The semiconductor laser device of the present invention includes such a resonator 90, but the notation of the resonator 90 in FIG. 3 accurately indicates the position of the resonator 90 in the longitudinal direction.

  In the present invention, the term “nitride semiconductor” is used as a general term for a group III-V compound semiconductor when the group V element is nitrogen, but is not limited to the case where the group V element is only nitrogen. Even if a part of nitrogen is substituted with another element, it is included in the nitride semiconductor.

<Separation of electrodes>
In the semiconductor laser device of the present invention, at least one of the p-side electrode 70 and the n-side electrode 80 is electrically separated into two or more regions by a divided region 95 that intersects the longitudinal direction of the resonator 90. Cost. Specifically, for example, as shown in FIGS. 1 and 3, the p-side electrode 70 (the p-side electrode continuously present in the longitudinal direction assuming the state before being separated by the divided region 95) is The p-side electrode 71 and the p-side electrode 72 are separated by a divided region 95 that intersects the longitudinal direction of the resonator 90. The p-side electrode 71 and the p-side electrode 72 are electrically separated from each other. For convenience, the region on the p-side electrode 71 side is called a first region 91, and the region on the p-side electrode 72 side is It shall be called the 2nd field 92. 1 and 3 show a mode in which the p-side electrode 70 is separated into two regions, the separation of such regions may be separated into two or more regions. Further, the n-side electrode 80 may be separated. In addition, since no electrode is formed in the divided region 95, each region separated by the divided region 95 is electrically separated.

  When current is injected into the first region 91 in the same manner as a normal semiconductor laser element, this region becomes a gain region that causes laser oscillation (in this case, the first region 91 is a non-short circuit described later). Area). On the other hand, if current injection is not performed on the second region 92, the second region 92 becomes a saturable absorption region. This saturable absorption region absorbs a part of the laser light oscillated in the gain region, and the amount of absorption is a region having an action that changes as the carrier density in this region increases and decreases. The semiconductor laser device of the present invention having a saturated absorption region has self-oscillation characteristics. Even when the electrodes are separated not only in two regions but also in three or more regions in this way, at least one region functioning as a gain region or a saturable absorption region is formed depending on the presence or absence of current injection and the size. Will be.

  Note that the p-type nitride semiconductor layer 40 has a feature that its electric resistance is extremely higher than that of the GaAs compound semiconductor or the n-type nitride semiconductor layer 20. For this reason, when the p-side electrode 70 is separated by the divided region 95, the width of the divided region 95 (here, “width” means a distance (length) parallel to the longitudinal direction of the resonator 90)). Even if the thickness is only about 1 to 10 μm, electrical separation is possible. The divided region 95 functions as a saturable absorption region because current injection is not performed as described above. However, since there is no electrode, carriers cannot be sufficiently swept out. Therefore, since the carrier lifetime is not shortened and it may be a simple absorption region, it is preferable to make the width of the divided region as small as possible from the viewpoint of self-excited oscillation characteristics. Therefore, it is preferable to electrically separate the p-side electrode 70 because the electrical separation can be performed even if the width of the divided region is made smaller than to electrically separate the n-side electrode 80. Note that electrical separation is also possible by removing the nitride semiconductor layer in the divided regions.

<Short circuit>
The electrode in at least one region separated by the divided region as described above is short-circuited with the electrode on the opposite side of the electrode to form a short-circuit region, and at least one region other than the short-circuited electrode These electrodes preferably form a non-shorted region that is not short-circuited with the electrode on the opposite side of the electrode. This will be specifically described with reference to FIGS. 1 and 3 as an example.

  That is, when current injection is performed on the first region 91 in the same manner as a normal semiconductor laser element, this region becomes a gain region that causes laser oscillation. In this case, the first region 91 is a non-short-circuit region as described above. This is because the current is injected without short-circuiting the p-side electrode 71 and the n-side electrode 80 (corresponding to the electrode opposite to the p-side electrode 71).

  On the other hand, the second region 92 is a saturable absorption region where no current is injected. In the second region 92, the p-side electrode 72 and the n-side electrode 80 (opposite of the p-side electrode 72). A short-circuit region as described above. Thus, by setting the saturable absorption region as a short-circuit region, it is possible to promote the sweeping of carriers generated in the active layer, thereby shortening the carrier life, which is preferable.

  In FIGS. 1 and 3, such a short circuit between the p-side electrode and the n-side electrode is not specifically shown. As a means for such a short circuit, for example, both wire bonding and conductive film are used. Various methods such as contact with electrodes can be used.

  On the other hand, the carrier lifetime can be controlled not only by electrically short-circuiting both electrodes as described above but also by applying a bias voltage. For example, in order to shorten the carrier lifetime, it is effective to apply a reverse bias voltage to the pn junction. This is because the application of the reverse bias voltage increases the internal electric field, and further expands the depletion layer to increase the electric field applied to the active layer, thereby facilitating the sweeping of carriers. However, considering the practicality of the semiconductor laser element, it is desirable to obtain self-excited oscillation characteristics only by short-circuiting the p-side electrode and the n-side electrode without applying a reverse bias voltage.

  In the present invention, it is possible to obtain self-oscillation characteristics (self-oscillation) if the carrier life is sufficiently short without short-circuiting the p-side electrode and the n-side electrode as described above. .

<Internal electric field>
The active layer of the semiconductor laser device of the present invention is at least partially different from the first internal electric field in the same direction as the first internal electric field due to the pn junction between the n-type semiconductor layer and the p-type semiconductor layer. A second internal electric field of a kind is generated. As a result, the semiconductor laser device of the present invention has a suitable self-excited oscillation characteristic. Hereinafter, the principle that the semiconductor laser device of the present invention can easily obtain the self-excited oscillation characteristic (easily self-excited oscillation) will be described.

  In the following description, the nitride semiconductor laser element 100 is taken as an example of the semiconductor laser element, the active layer 30 is composed of a nitride semiconductor crystal having a wurtzite crystal structure, and the upper surface thereof is a (000-1) plane. The n-type nitride semiconductor layer 20 which is an n-type semiconductor layer is positioned in the [000 + 1] direction of the active layer 30, and the p-type nitride semiconductor layer 40 which is a p-type semiconductor layer is [000− 1] The case where it is located in the direction will be described.

  First, a nitride semiconductor crystal having a wurtzite crystal structure has a bond structure as shown in FIG. In the figure, III represents a group III element, for example, Al, Ga, In and the like. In the figure, N represents a nitrogen atom. In addition, since the direction from the group III element located in the center of the figure to the N located in the center of the figure is generally defined as the [000 + 1] direction, and the direction opposite to 180 ° is defined as the [000-1] direction, But follow this definition.

  In such a crystal structure, if no distortion occurs, the electric dipole moments cancel each other, so that no polarization appears. However, when the crystal lattice is distorted by pressure, tension, etc., the electric dipole moment cannot be completely canceled and polarization appears. An electric field generated by this polarization is generally called a piezoelectric field. In the above case, this piezoelectric field is caused by lattice distortion.

  This piezo electric field has a direction similar to a normal electric field, and the direction is strain generated by tensile stress (tensile strain) or strain generated by compressive stress (compressive strain). It depends on whether it changes. As described above, when the upper surface of the active layer is the (000-1) plane and the compressive strain is applied in the growth plane of the active layer, the direction of the piezoelectric field is the direction of [000-1], that is, crystal growth. Occurs in the same direction as On the other hand, when tensile strain is applied in the growth plane, the direction of the piezoelectric field is generated in the [000 + 1] direction opposite to the above, that is, the direction opposite to the direction of crystal growth.

  On the other hand, since the p-type semiconductor layer and the n-type semiconductor layer are stacked on the upper and lower sides of the active layer, the pn of the p-type semiconductor layer and the n-type semiconductor layer is used as the internal electric field in addition to the piezoelectric field described above. An internal electric field is also generated by the junction. In the present invention, for the sake of convenience, the internal electric field due to the pn junction is sometimes referred to as a first internal electric field, and an internal electric field different from the first internal electric field, such as a piezo electric field, is sometimes referred to as a second internal electric field. The direction of the internal electric field by the pn junction, that is, the first internal electric field is generated in the direction from the n-type semiconductor to the p-type semiconductor.

  Therefore, as is clear from the above, the direction of the internal electric field (first internal electric field) and the piezoelectric electric field (second internal electric field) due to the pn junction is such that the upper surface of the active layer is the (000 + 1) plane or the (000-1) plane. Depending on whether the strain applied during crystal growth of the active layer is a compressive strain or a tensile strain, and whether the upper surface side of the active layer is a p-type semiconductor layer or an n-type semiconductor layer. Will change.

  Therefore, when the substrate is made of GaN and the active layer is made of InGaN, since InGaN has a larger lattice constant than GaN, compressive strain is applied in the crystal growth plane of the active layer (that is, the active layer is compressed). If the upper surface of the active layer is the (000-1) plane, the piezoelectric field is generated in the [000-1] direction, which is the same direction as the crystal growth direction. Since the internal electric field due to the pn junction is in the direction from the n-type semiconductor layer to the p-type semiconductor layer, the p-type semiconductor layer is arranged in the [000-1] direction on the upper surface side of the active layer, and [000 + 1] on the opposite side. If the n-type semiconductor layer is arranged in the direction, the internal electric field due to the pn junction is generated in the [000-1] direction of the active layer, and the direction of the piezoelectric electric field and the direction of the internal electric field due to the pn junction are generated in the same direction. Become. That is, the direction of the first internal electric field and the direction of the second internal electric field are the same direction.

  In addition, as long as the direction of the first internal electric field and the direction of the second internal electric field are the same, the effect of the present invention can be obtained. Therefore, when the upper surface of the active layer is a (000 + 1) plane, It is preferable that the stacking order of the p-type semiconductor layer and the n-type semiconductor layer with respect to the active layer is reversed and the p-type semiconductor layer is positioned in the [000-1] direction of the active layer.

  Usually, the active layer has a smaller band gap than the surrounding layers, and a material having a smaller band cap tends to have a larger lattice constant. For this reason, the active layer is usually subjected to compressive strain during crystal growth. When a nitride semiconductor crystal having a wurtzite crystal structure is subjected to compressive strain, a piezoelectric field is generated in the [000-1] direction. Therefore, the direction of the piezoelectric field generated in the active layer and the direction of the internal electric field due to the pn junction are the same direction. In order to achieve this, a p-type semiconductor layer may be disposed in the [000-1] direction of the active layer, and an n-type semiconductor layer may be disposed in the [000 + 1] direction on the opposite side.

  Here, FIG. 5 schematically shows the relationship between the difference between the direction of the piezo electric field and the direction of the internal electric field by the pn junction and the band structure. 5A shows a case where the direction of the piezo electric field is the same as the direction of the internal electric field due to the pn junction, and FIG. 5B shows the direction where the direction of the piezo electric field is opposite to the direction of the internal electric field due to the pn junction. (C) shows a case where no piezoelectric field is generated and only an internal electric field due to a pn junction exists.

  When the direction of the piezo electric field and the direction of the internal electric field due to the pn junction occur in opposite directions, when the piezo electric field is strong and is applied to the active layer, the band structure as shown in FIG. Will be trapped easily. Originally, electrons are transported to the n-type semiconductor layer side and holes are transported to the p-type semiconductor layer side due to the internal electric field by the pn junction, so that the carrier lifetime is shortened, whereas the direction of the internal electric field of the pn junction is The phenomenon that the carrier life is not shortened due to the carrier transport being hindered by applying the piezoelectric field in the opposite direction to the active layer is shown.

  On the other hand, when there is no piezo electric field, as can be seen from the band structure as shown in FIG. 5C, electrons are moved to the n-type semiconductor layer side by the action of the internal electric field by the pn junction, and the holes are p It is easy to be swept out to the type semiconductor layer side.

  On the other hand, when the direction of the piezo electric field and the direction of the internal electric field by the pn junction occur in the same direction ((a) in FIG. 5), the internal electric field by the pn junction (first internal electric field) and the piezoelectric electric field (second electric field) Electrons are transported to the n-type semiconductor layer side and holes are transported to the p-type semiconductor layer side due to the action of both electric fields by the internal electric field), so that carriers are more likely to be swept out of the active layer. I understand. If the carriers in the active layer are easily swept out, the carrier lifetime is shortened.

  Accordingly, in the semiconductor laser device of the present invention, the active layer has a second type different from the first internal electric field in the same direction as the direction of the first internal electric field by the pn junction between the n-type semiconductor layer and the p-type semiconductor layer. If an internal electric field (that is, a piezo electric field as described above) is generated, carriers generated in the active layer by light absorption in the saturable absorption region of the second region 92 have a short lifetime, and thus self-oscillation occurs. It is easy to happen.

  Such a second internal electric field does not necessarily need to be generated in the entire active layer, and if it occurs in at least a part of the active layer, the above-described effects can be obtained. This mainly affects the self-excited oscillation characteristics in a region where carriers in the active layer are concentrated, and at least such a second internal electric field is generated in such a region. This is because the effects of the present invention can be obtained.

  FIG. 5 assumes a case where the active layer is completely included in the depletion layer. The greater the proportion of the active layer contained in the depletion layer, the more the carrier sweeping is promoted and the self-excited oscillation is more likely to occur.

  On the other hand, when the active layer has a quantum well structure or a multiple quantum well structure having one or more well layers and one or more barrier layers, the pn of the n-type semiconductor layer and the p-type semiconductor layer in the well layer The effect of the present invention can be obtained if a second internal electric field of a kind different from the first internal electric field is generated in the same direction as the direction of the first internal electric field by the junction. As described above, the effect of the present invention can be obtained by setting the internal electric field state in the well layer as described above. As described above, the self-excited oscillation characteristics are mainly affected by the concentration of carriers. This is because carriers are concentrated in the well layer in the quantum well structure or the multiple quantum well structure.

  On the other hand, the piezoelectric electric field resulting from lattice distortion has been described above as the second internal electric field. However, the effect of the present invention is that the first internal electric field and the direction of the first internal electric field by the pn junction are the same as the first internal electric field. Is obtained as long as a different type of second internal electric field is generated in at least a part of the active layer. Therefore, the second internal electric field is not limited to the piezo electric field due to lattice distortion. Various internal electric fields are included.

  For example, in a nitride semiconductor crystal having a wurtzite crystal structure, spontaneous polarization occurs due to the asymmetry of the crystal even when no strain is applied. An internal electric field generated by such spontaneous polarization can also be cited as the second internal electric field. However, since the magnitude of spontaneous polarization is substantially the same between GaN and InN, spontaneous polarization can be ignored when the active layer is InGaN.

  Even when the active layer has the upper surface in the direction between the [000-1] direction and the [000 + 1] direction, a piezoelectric field, that is, a second internal electric field that affects the band structure is generated in the crystal growth direction. appear. The direction of this piezo electric field is determined by the crystal orientation, and the effect of the present invention can be obtained if the orientation is the same as the direction of the internal electric field by the pn junction.

  The piezoelectric field is generated without being limited only when the active layer has the wurtzite crystal structure as described above. For example, even when the active layer is composed of a nitride semiconductor crystal having a zinc blende type crystal structure or a GaAs semiconductor, the growth direction is the <111> direction and the lattice strain is reduced. In such a case, a piezo electric field is generated in the growth direction. For this reason, the effect of the present invention can be obtained if the direction of the piezoelectric field is the same as the direction of the internal electric field by the pn junction.

  Furthermore, as long as the active layer is in the internal electric field state as described above, the effects of the present invention can be obtained, and the structure and composition of the p-type semiconductor layer and the structure and composition of the n-type semiconductor layer are not particularly limited. Therefore, the crystal orientation of the p-type semiconductor layer and the n-type semiconductor layer may not be the same crystal orientation as that of the active layer. For example, the upper surface may be a (000 + 1) plane.

  In addition, the p-type semiconductor layer and the n-type semiconductor layer may not be formed of a nitride semiconductor crystal having a wurtzite crystal structure, for example, a nitride semiconductor having a zincblende crystal structure, wurtzite An oxide semiconductor having an ore-type crystal structure can also be used. Therefore, the semiconductor laser device of the present invention is not limited to a nitride semiconductor laser device (a laser device in which the semiconductor layer is formed of a nitride semiconductor layer).

  However, the n-type semiconductor layer, the active layer, and the p-type semiconductor layer are preferably made of the same material having the same crystal structure and the same crystal orientation. This is because the highest quality crystal can be easily produced. Therefore, when the active layer of the present invention is composed of a nitride semiconductor crystal having a wurtzite crystal structure whose upper surface is a (000-1) plane, the n-type semiconductor layer and the p-type semiconductor layer are also the same. It is preferable that the upper surface is made of a nitride semiconductor crystal having a wurtzite crystal structure having a (000-1) plane. In the present invention, having the same crystal orientation means that the crystal orientations are the same when the crystal orientations on the upper surfaces of the crystals constituting each layer (including the substrate) are the same. .

  Moreover, since the effect of the present invention can be obtained as long as the active layer is in the internal electric field state as described above, the substrate is not particularly limited. For example, a nitride semiconductor layer having a wurtzite crystal structure having a (000-1) plane on the sapphire (0001) plane can be formed on the sapphire (0001) plane. However, the substrate is also preferably made of the same material having the same crystal structure and the same crystal orientation as the semiconductor layer stacked thereon. This is because the highest quality semiconductor layer can be easily manufactured. In particular, the crystal orientation of the substrate and the active layer is preferably the same crystal orientation. This is because the highest quality active layer can be easily produced.

  That is, when the active layer is formed of a nitride semiconductor crystal having a wurtzite crystal structure with the upper surface being a (000-1) plane, a nitride semiconductor substrate having an upper surface having a (000-1) plane is used. It is particularly preferable to use a GaN substrate that is available at a relatively low cost.

<Specific structure of semiconductor laser element>
In the semiconductor laser device of the present invention, for example, a plurality of nitride semiconductor layers are formed as semiconductor layers on a substrate 10 as shown in FIGS. That is, the semiconductor layer includes at least an n-type nitride semiconductor layer 20 which is an n-type semiconductor layer, an active layer 30 made of a nitride semiconductor crystal, and a p-type nitride semiconductor layer 40 which is a p-type semiconductor layer. included. These have a structure in which an n-type semiconductor layer, an active layer 30 and a p-type semiconductor layer are stacked in this order from the substrate 10 side.

  Further, a part of the semiconductor layer (preferably p-type nitride semiconductor layer 40) is removed, and a striped (elongated) ridge stripe portion 55 is provided.

  Such a semiconductor laser device of the present invention can include any other layer as long as the above semiconductor layer is included on the substrate. Hereinafter, each configuration will be further described in detail.

<Board>
The substrate 10 is not particularly limited as described above, but is preferably composed of a nitride semiconductor crystal, and the nitride semiconductor crystal preferably has a wurtzite crystal structure and is preferably GaN. preferable. More preferably, the substrate 10 has a wurtzite crystal structure, and is preferably composed of GaN whose upper surface is a (000-1) plane.

  In addition to the above, examples of such a substrate 10 include a wurtzite type and a zincblende type as the crystal structure, and examples of the material include sapphire, SiC, GaAs, Si, AlN, AlGaN, and InGaN.

  As described above, since it is easiest to generate a piezo electric field in the same direction as the internal electric field due to the pn junction as the active layer 30, the upper surface of such a substrate 10 is the (000-1) plane. GaN having a wurtzite crystal structure is most preferred.

<N-type semiconductor layer>
The n-type semiconductor layer is preferably an n-type nitride semiconductor layer. Such an n-type nitride semiconductor layer 20 includes, for example, an n-type buffer layer, an n-type contact layer, an n-type cladding layer, an n-type guide layer, and the like. The n-type buffer layer and the n-type contact layer can be omitted. When a GaN substrate is used as the substrate 10, an n-type cladding layer can be formed directly on the substrate 10. In addition to this, various structures can be used without particular limitation, such as providing a hole block layer or providing a layer having a non-n-type conductivity. In addition, the n-type nitride semiconductor layer 20 includes any one or more of group IV elements such as Si and O or group VI elements as n-type impurities. Of these, Si is preferable. The impurity concentration can be in the range of about 5 × 10 ¹⁶ cm ⁻³ to 1 × 10 ²¹ cm ⁻³ . Preferably, it is about 1 × 10 ¹⁷ cm ^{−3 to} 5 × 10 ¹⁸ cm ⁻³ .

  Such an n-type nitride semiconductor layer which is an n-type semiconductor layer is preferably composed of a nitride semiconductor crystal having a wurtzite crystal structure. This is because, as described above, the same crystal structure and the same crystal orientation as those of the substrate and the active layer are preferable. Accordingly, the n-type semiconductor layer is most preferably a nitride semiconductor layer composed of a nitride semiconductor crystal having a wurtzite crystal structure whose upper surface is a (000-1) plane.

<P-type semiconductor layer>
The p-type semiconductor layer is preferably a p-type nitride semiconductor layer. Such a p-type nitride semiconductor layer 40 includes, for example, a p-type carrier block layer, a p-type cladding layer, a p-type guide layer, a p-type contact layer, and the like. The p-type guide layer and the p-type contact layer can be omitted. In addition, various structures can be used without particular limitation, such as providing an intermediate layer between the active layer 30 and the p-type carrier block layer, or providing a part of the layer that is not p-type in conductivity.

The p-type nitride semiconductor layer 40 includes any one or more elements such as Mg, Be, Zn, and C as p-type impurities. Among these, Mg or C is preferable. The impurity concentration can be in the range of about 5 × 10 ¹⁶ cm ⁻³ to 1 × 10 ²¹ cm ⁻³ . Preferably, it is about 5 × 10 ¹⁸ cm ⁻³ to 2 × 10 ²⁰ cm ⁻³ .

  Such a p-type nitride semiconductor layer that is a p-type semiconductor layer is preferably composed of a nitride semiconductor crystal having a wurtzite crystal structure. This is because, as described above, the same crystal structure and the same crystal orientation as those of the substrate and the active layer are preferable. Therefore, the p-type semiconductor layer is most preferably a nitride semiconductor layer composed of a nitride semiconductor crystal having a wurtzite crystal structure whose upper surface is a (000-1) plane.

<Active layer>
As described above, the active layer 30 is provided between the n-type semiconductor layer and the p-type semiconductor layer. Such an active layer 30 preferably has a quantum well structure having a well layer and a barrier layer. The quantum well structure may be a multiple quantum well (MQW) structure having a plurality of well layers and a plurality of barrier layers.

The conductivity type of the active layer is not particularly limited, and impurity doping may not be performed. A p-type impurity and / or an n-type impurity may be 5 × 10 ¹⁶ cm ⁻³ to 1 × 10 ²¹ cm ^−3. You may dope in the range of about.

  As described above, such an active layer is preferably composed of a nitride semiconductor crystal having a wurtzite crystal structure in consideration of generation of the second internal electric field, and is composed of InGaN subjected to compressive strain. Is particularly preferred.

<Nitride semiconductor crystal composition, etc.>
Examples of the nitride semiconductor crystal constituting the n-type semiconductor layer, the active layer, and the p-type semiconductor layer can include GaN, AlGaN, InGaN, AlN, InN, AlInGaN, etc., in addition to those specifically exemplified above. . Furthermore, as such a nitride semiconductor crystal, one in which B (boron) is partially substituted as a group III element may be used, or a part of N (nitrogen) as a group V element may be P ( Phosphorus) or As (arsenic) may be used. The material, composition, and layer thickness to be used can be appropriately selected in consideration of the laser wavelength band, optical confinement, manufacturing convenience, and the like.

  All layers are vapor-phase growth methods such as MOCVD (Metal Organic Chemical Vapor Deposition), MBE (Molecular Beam Epitaxy) and sputtering, and crystals in supercritical fluids. It can be produced using a hydrothermal synthesis method or a liquid phase growth method such as a flux method, etc., and each of these growth methods can be used alone or in combination with two or more growth methods as appropriate. The growth method can be used. When sapphire is used for the substrate, it is preferable to use the MBE method because it has excellent controllability of the growth surface.

  Further, the n-type semiconductor layer and the p-type semiconductor layer can be made of a material such as ZnO or GaAs instead of the nitride semiconductor crystal.

<Ridge structure>
In the semiconductor laser device of the present invention, as a preferred embodiment, the stripe-shaped (elongated) ridge stripe portion 55 is preferably provided on at least a part of the p-type semiconductor layer or the n-type semiconductor layer. The ridge stripe portion 55 has a current confinement function and a waveguide function that performs optical confinement in the lateral direction with a refractive index difference inside and outside the stripe.

  The width of the ridge stripe portion 55 (the length in the horizontal direction in the cross section parallel to the end face) is about 1.0 μm to 20.0 μm. When it is necessary to set the laser light to a single mode for use as a light source in an optical disc system, the width of the ridge stripe portion 55 is preferably about 1.0 μm to 3.0 μm. When a multimode may be used for a display application or the like, the width of the ridge stripe portion 55 is about 2.0 μm to 20.0 μm in order to increase the maximum light output. When the cross-sectional shape of the ridge stripe portion 55 (the cross-sectional shape parallel to the end face) is a trapezoid, the width of the ridge stripe portion 55 is the length of the upper base.

  The height of the ridge stripe portion 55 (the length in the longitudinal direction in the cross section parallel to the end face) is about 0.1 μm to 2.0 μm. Since the width and height of the ridge stripe portion 55 greatly affect the optical confinement in the lateral direction, it is preferable to set in consideration of this point.

<Resonator and end face>
As shown in FIG. 1, the semiconductor laser device of the present invention has a resonator having an end surface 110 and an end surface 120 as resonator end surfaces. Such end surface 110 and end surface 120 are preferably surfaces perpendicular to the growth main surface of the substrate 10. Further, when the substrate 10 is made of GaN and the main growth surface is a {0001} plane, the end face 110 and the end face 120 are a {1-100} plane or a {11-20} plane, respectively. be able to.

  In addition, when the end face 110 and the end face 120 are formed by cleavage, it is particularly preferable to use a {1-100} plane in consideration of the flatness of the cleavage plane. Moreover, as a method for forming such an end face, there can be mentioned a method for forming an end face of an etched mirror using dry etching in addition to cleavage.

<Insulating film>
An insulating film 60 is preferably formed on the upper surface of the p-type semiconductor layer (that is, the p-side electrode side). The insulating film 60 needs to be formed so as to expose the p-type semiconductor layer in at least a part of the upper surface portion of the ridge stripe portion 55 (that is, the portion in contact with the p-side electrode).

  The insulating film 60 can be composed of oxides such as Si, Ti, Ta, Al, Zr, Nb, Hf, and Zn, nitrides, oxynitrides, and the like. Such an insulating film 60 may be formed as a single layer or may have a laminated structure of two or more layers. The constituent materials can be used in various forms such as single crystal, polycrystal, amorphous, or a mixed state thereof. In particular, considering the ease of production, adhesion, and thermal stability, the insulating film 60 is composed of Si oxide, Zr oxide, Al nitride, Si nitride, Si oxide and Ti oxidation. It is preferable to constitute a laminated structure with an object. The thickness of the insulating film 60 is about 50 to 5000 mm.

<P-side electrode and its separation>
A p-side electrode 70 is formed on the upper surface (the side far from the substrate) of the insulating film 60. The p-side electrode 70 is in contact with the p-type semiconductor layer at the upper surface portion of the ridge stripe portion 55. In other words, the p-side electrode 70 is preferably insulated from the p-type semiconductor layer by sandwiching the insulating film 60 except for the upper surface portion of the ridge stripe portion 55.

  As described above, the p-side electrode 70 is electrically separated into two or more regions by the divided region 95 intersecting with the longitudinal direction of the resonator as shown in FIGS. With such a structure, each region (in the case of FIG. 1, the first region 91 and the second region 92 correspond) can be electrically driven independently.

  In the embodiment shown in FIG. 1, the first region 91 where the p-side electrode 71 is formed and the second region 92 where the p-side electrode 72 is formed are separated into two regions, and the length in the longitudinal direction is The second region 92 is shorter. In this case, by injecting current only into the first region 91, the first region 91 can be a gain region, and no current can be injected into the second region 92 to be a saturable absorption region. However, this is an example, and how the length of each region (that is, the length of each separated electrode) is determined with respect to the length of the resonator 90 in the longitudinal direction (also referred to as “resonator length”). The allocation can be appropriately designed in consideration of various desired characteristics.

  For example, as the second region 92 is lengthened, the total amount of light absorption in the resonator increases, the threshold current and slope efficiency deteriorate, and the light output range in which a sharp rise of the light output near the threshold current occurs. However, there is a merit that it becomes easy to show the self-excited oscillation characteristic (that is, self-excited oscillation becomes easy). Not only in this case, the basic characteristics of the laser such as the threshold current and the slope efficiency and the likelihood of self-oscillation are always in a trade-off relationship. The only way to break this relationship is to shorten the carrier lifetime in the saturable absorption region and make the saturable absorption region as small as possible within the range showing the self-excited oscillation characteristics. Accordingly, the second region 92 is preferably shorter, and is preferably at least shorter than the first region 91. More preferably, the second region 92 is further shorter than the length of about 1/10 of the first region 91. Even in the case of separation into more than two regions, it is preferable to design appropriately considering the same phenomenon.

  In addition, as above-mentioned, it is preferable that the p side electrode and n side electrode of the area | region (in this case 2nd area | region 92) used as a saturable absorption area | region are electrically short-circuited. Such short-circuiting can be performed, for example, by directly wire-bonding the corresponding p-side electrode and n-side electrode, or via a mounting stem terminal between the two electrodes. In addition, various methods such as through a conductive thin film provided on an end face can be used.

  In addition, a bias voltage can be applied to the p-side electrode and the n-side electrode in the saturable absorption region without being electrically short-circuited as described above. In this case, when a reverse bias voltage is applied to the pn junction, the carrier lifetime is shortened and the self-excited oscillation characteristics can be improved. Even in this case, the semiconductor laser device of the present invention has an effect that the bias voltage required to obtain the same self-excited oscillation characteristic as compared with the conventional semiconductor laser device can be reduced. Even when only a forward bias voltage can be applied due to the convenience of a system using a semiconductor laser device, the semiconductor laser device of the present invention exhibits self-oscillation characteristics as compared with a conventional nitride semiconductor laser device. The effect is easy. Even when the saturable absorption region is used for laser light detection, the photoinduced current is increased and the detection accuracy is improved. Therefore, the semiconductor laser device of the present invention can be suitably used for such applications.

  Such a p-side electrode 70 is made of, for example, metals such as Pd (palladium), Ni (nickel), Pt (platinum), Au (gold), Mo (molybdenum), Ir (iridium), Rh (rhodium), and the like. It can be comprised from the alloy containing at least 1 sort (s) of a metal. Moreover, as such a p-side electrode 70, the above metals or alloys may be formed as a single layer, or may be formed as a laminated structure of two or more layers. Among them, since the contact resistance can be reduced and the stability is high, a combination of Pd / Mo, Ni / Au, Ni / Au / Pt, and Ni / Au / Pd (the order of stacking is that the left metal is the semiconductor layer side) ) Is preferred. When the p-side electrode 70 is configured in a laminated structure, the thickness of each layer can be about 50 to 5000 mm. On the other hand, the thickness of the entire p-side electrode is preferably 1000 to 50000 mm.

  Such a p-side electrode 70 can also be formed so as to be in contact with the substrate in the order of stacking the semiconductor layers.

<N-side electrode>
When the substrate 10 is a conductive substrate such as a GaN substrate, the n-side electrode 80 is, as shown in FIGS. 1 and 2, the back surface of the substrate 10 (the surface opposite to the surface on which the semiconductor layers are stacked). It can be formed so as to be in contact with the substrate 10. In this case, the n-side electrode 80 may be formed on the entire back surface of the substrate 10 or a part thereof. From the viewpoint of suppressing an increase in driving voltage, it is preferably formed on the entire surface.

  On the other hand, when the substrate 10 is an insulating substrate such as a sapphire substrate, the n-side semiconductor layer is contacted with the n-type semiconductor layer on the n-type semiconductor layer exposed by removing another semiconductor layer by etching. It is necessary to form an electrode. Therefore, considering the ease of production of the n-side electrode, it is preferable to use a GaN substrate as the substrate 10.

  The n-side electrode 80 is made of a metal such as Hf, Al, Mo, Pt, Au, W (tungsten), Ti (titanium), Cr (chromium), or an alloy containing at least one of these metals. be able to. Moreover, as such an n-side electrode 80, the above metals or alloys may be formed as a single layer, or may be formed as a laminated structure of two or more layers. Among these, a combination of Hf / Al / Mo / Pt / Au and Ti / Pt / Au is preferable because contact resistance can be reduced and stability is high (the left metal is the semiconductor layer side). When the n-side electrode 80 is configured in a laminated structure, the thickness of each layer may be about 50 to 5000 mm. On the other hand, the thickness of the entire n-side electrode is preferably 1000 to 50000 mm.

  Such an n-side electrode 80 can also be formed so as to be in contact with the n-type semiconductor layer according to the stacking order of the semiconductor layers.

<Electrode patterning>
The insulating film 60, the p-side electrode 70, and the n-side electrode 80 may be appropriately patterned in consideration of convenience at the mounting stage. As long as the insulating film 60, the p-side electrode 70, and the n-side electrode 80 have their respective functions, the thickness, shape, pattern, and the like can be appropriately changed. For example, the p-side electrode 70 may have a shape that partially or entirely surrounds the side surface of the ridge stripe portion 55. With this configuration, it is possible to reduce the drive voltage. In particular, the p-side electrode 70 has a wire in a region away from the ridge stripe portion 55 so that wire bonding can be easily performed to each of the first region 91 (p-side electrode 71) and the second region 92 (p-side electrode 72). It is preferable to have a pad electrode for bonding.

<Coating film>
The end face 110 and the end face 120 are respectively provided with a coating film 200 and a coating film 300 in order to improve the COD (Catastrophic Optical Damage: instantaneous optical damage) level and reflectivity to obtain desired laser characteristics. Can be formed. As in a normal semiconductor laser element, one reflectance is set lower than the other, and that side is set as a light emitting side, and a side having a high reflectance is set as a light reflecting side. The reflectance is about 10% to 70% on the light emitting side and about 70 to 99% on the light reflecting side. If the reflectance differs between the two end faces in this way, the light intensity distribution inside the resonator becomes asymmetric, so depending on where in the resonator the saturable absorption region is placed, the self-excited oscillation characteristics and The basic laser characteristics are different. Therefore, it is necessary to appropriately consider the arrangement according to practical specifications.

  The coating film 200 and the coating film 300 include oxides such as Al, Si, Zr, Ta, Ga, Y, Nb, Hf, Zn, and Ti, nitrides or oxynitrides such as Al, Si, Ga, and B. And may be a single layer or a multilayer in which two or more layers are stacked. Such a coating film preferably has a thickness of usually about 50 to 1000 nm.

<Cavity length and chip width>
The resonator length (length in the longitudinal direction) of the semiconductor laser device of the present invention can be set to a length of about 300 μm to 3000 μm. Preferably, it is about 400 μm to 1000 μm. The chip width of the semiconductor laser device of the present invention (the length in the lateral direction when the resonator length is the longitudinal direction) is about 100 μm to 1000 μm. Preferably, it is about 150 μm to 400 μm.

<Manufacturing method>
A method for manufacturing a semiconductor laser device of the present invention will be described with reference to FIGS. 1 to 3 by taking as an example a case where a nitride semiconductor layer is formed as a semiconductor layer.

  First, the n-type nitride semiconductor layer 20, the active layer 30, and the p-type nitride semiconductor layer 40 are sequentially grown on the substrate 10 using a crystal growth method such as MOCVD. In addition to the MOCVD method, a vapor phase growth method such as an MBE method or a sputtering method, a liquid phase growth method such as a hydrothermal synthesis method or a flux method for crystal growth in a supercritical fluid, or the like can also be used. Two or more growth methods can also be combined. As described above, the method for forming the nitride semiconductor layer is not particularly limited, and various growth methods can be used. In order to generate the second internal electric field in the active layer, it is necessary to set the layer thickness to a critical thickness or less. The critical film thickness is a layer thickness at which the strain is relaxed due to the occurrence of cracks, dislocations, etc. in the crystal at a film thickness larger than that. The value of the critical film thickness varies depending on the amount of strain. For example, if InGaN is distorted with respect to GaN, the critical film thickness decreases as the In composition increases. If the thickness is equal to or less than the critical thickness, the active layer can maintain the strain, so that a second internal electric field composed of a piezoelectric field can be generated. The critical film thickness can be known in advance by an X-ray diffraction method or the like.

  Next, a striped (elongated) ridge stripe portion 55 is formed on at least a part of the p-type nitride semiconductor layer 40 by using a photolithography technique, an etching technique, or the like. Then, by using various vacuum deposition methods, sputtering methods, CVD (Chemical Vapor Deposition) methods, etc., on the p-type nitride semiconductor layer 40, the side surface portion of the ridge stripe portion 55 and the plane following it. An insulating film 60 is formed so as to cover the part.

  Subsequently, the p-side electrode 70 that contacts the p-type nitride semiconductor layer 40 is formed on the insulating film 60 by using various vacuum deposition methods, sputtering methods, CVD methods, and the like. In this case, in order to improve the characteristics, annealing may be performed at a temperature of about 100 ° C. to 500 ° C. after the formation of the p-side electrode (metal film). By performing such an annealing process, a good ohmic electrode can be obtained.

  On the other hand, a masking process or the like is applied to the p-side electrode 70 in order to provide the divided region 95 where no electrode is formed in a direction intersecting the longitudinal direction of the resonator. As another method, the divided region can be provided by forming the electrode and then removing the electrode by wet etching or the like using a photolithography technique without performing a masking process. Furthermore, not only the electrode but also the nitride semiconductor layer located in the divided region can be removed.

  Then, in order to make it easy to divide the substrate 10, the back surface of the substrate 10 (the surface opposite to the side on which the nitride semiconductor layer is formed) is ground or polished, so that the substrate 10 has a thickness of about 70 μm to 300 μm. Until thin.

  Then, the n-side electrode 80 is formed on the back surface of the substrate 10 using various vacuum deposition methods, sputtering methods, CVD methods, and the like. In addition, before the n-side electrode 80 is formed, the adhesion between the n-side electrode 80 and the substrate 10 can be improved by cleaning the back surface of the substrate 10 by dry etching, ashing, reverse sputtering, or the like. Similarly to the p-side electrode 70, annealing may be performed at a temperature of about 100 ° C. to 500 ° C. after the n-side electrode 80 (metal film) is formed in order to improve the characteristics. By performing such an annealing treatment, a good ohmic electrode can be obtained as with the p-side electrode 70.

A wafer is formed by the above process (wafer process).
Next, the wafer obtained in the above process is divided into bars (bar division) by cleavage. Specifically, first, a scribe line is formed by diamond points or the like on at least one of the front surface and the back surface of the wafer. At this time, it is necessary to insert a scribe line at a position where a desired electrode pattern can be obtained. Further, by adjusting the patterning of the electrodes and the bar dividing position, a structure in which the p-side electrode 70 is not formed in the vicinity of the resonator end face can be obtained. With such a structure, device characteristics may be improved.

  The scribe line formed as described above serves as an auxiliary line for cleavage. Also, as a different method, the same role can be obtained by providing a recessed groove in advance by dry etching or the like without depending on the scribe line. The scribe line only needs to be at least at the edge of the wafer. However, by providing the scribe line inside the wafer in a broken line shape, the linearity of cleavage can be improved. Then, after the scribe line is formed, cleavage can be performed by applying an appropriate force to the wafer. The cleavage plane is preferably a plane perpendicular to the growth main surface of the substrate 10 (growth surface of the nitride semiconductor layer).

  At this time, the resonator length of the semiconductor laser element is defined by the bar division position. As described above, the resonator length can be about 300 μm to 3000 μm. Preferably, it is about 400 μm to 1000 μm.

  Next, as shown in FIG. 1, a coating film 200 and a coating film 300 are formed on the end surface 110 and the end surface 120 formed by bar division, respectively. The coating film 200 and the coating film 300 can be formed by various sputtering methods such as ECR (Electron Cyclotron Resonance) sputtering method and magnetron sputtering method. Two or more sputtering methods may be combined.

  In addition, plasma irradiation or heating using a gas such as argon, oxygen, nitrogen, hydrogen or a mixed gas containing two or more of these gases at least at one timing before and after the coating film is formed. Processing may be performed.

  Subsequently, the bar-shaped element (not shown) on which the coating film 200 and the coating film 300 are formed is divided into chips (chip division). At this time, the chip width is defined by the chip division position. As described above, the chip width can be about 100 μm to 1000 μm. Preferably, it is about 150 μm to 400 μm. The chip dividing method may be a scribing method for forming a scribe line, similar to the method used for bar division. This chip division is preferably performed in a direction perpendicular to the direction of bar division. In this way, the semiconductor laser device of the present invention is manufactured.

  The semiconductor laser device of the present invention obtained by the above manufacturing method is electrically connected to a stem having a + (plus) terminal and a-(minus) terminal using solder, silver paste, or the like. Is done.

  When the semiconductor laser device is mounted by the junction-up method, the n-side electrode 80 and the stem body are electrically connected, and the p-side electrode and the + -side terminal of the first region, which is the gain region, are connected via a bonding wire. Connect. When the p-side electrode in the second region corresponding to the saturable absorption region is connected to the negative terminal via a bonding wire, it is electrically short-circuited between the negative electrode connected to the negative terminal. . Further, the p-side electrode in the second region can be electrically short-circuited with the n-side electrode by connecting to the stem body connected to the n-side electrode.

  Further, a submount for improving heat dissipation can be provided between the semiconductor laser element and the stem. In this case, the submount and the n-side electrode 80 are electrically connected, and the submount and the -side terminal of the stem may be wire-bonded. If the p-side electrode in the second region corresponding to the saturable absorption region is connected to the submount via a bonding wire, an electrical short circuit can be achieved.

  After wire bonding, cap sealing is performed in a dry air atmosphere to assemble a can package type semiconductor laser device.

<Application>
The semiconductor laser device of the present invention has good self-oscillation characteristics and can easily perform self-oscillation. For this reason, since it is not necessary to apply a reverse bias to the saturable absorption region, the system can be simplified and miniaturized when used as a light source for a BD. In addition, since the self-excited oscillation occurs even if the saturable absorption region is reduced, it is possible to suppress a sudden rise in the optical output near the threshold current.

  Furthermore, since the semiconductor laser device of the present invention has such excellent characteristics, it can be used very suitably for an optical disc apparatus by using it as a light source (especially a reading light source). Moreover, it can be used very suitably also in an image display device. As described above, since the multi-wavelength mode oscillation state is brought about not only in the optical disc use such as BD but also in the display use for displaying an image, there is an effect of reducing speckle noise. It can be used very suitably in the application.

  On the other hand, the semiconductor laser device of the present invention can be used very favorably also in a semiconductor laser device that uses a light-induced current flowing in a saturable absorption region for laser light output detection.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Example 1>
6 and 7 schematically showing the structure of the semiconductor laser device of this example (however, the thickness of each layer in these figures may not reflect the actual thickness of this example). I will explain.

  First, an n-type GaN substrate was used as the substrate 10. The crystal orientation of the main growth surface of the substrate 10 was the (000-1) plane (see FIG. 4).

  Further, the n-type nitride semiconductor layer 20 as the n-type semiconductor layer is configured to include an n-type GaN layer 21, an n-type cladding layer 22, and an n-type guide layer 23. The p-type nitride semiconductor layer 40 as the p-type semiconductor layer is configured to include a carrier block layer 41, a p-type guide layer 42, a p-type cladding layer 43 and a p-type contact layer 44.

Specifically, an n-type GaN layer 21 having a thickness of 0.2 μm (200 nm) and an n-type Al _0.03 Ga _0.97 N having a thickness of 2.2 μm (2200 nm) are formed on the substrate 10 by MOCVD. N-type cladding layer 22, n-type guide layer 23 made of n-type GaN having a thickness of 0.17 μm (170 nm), active layer 30, p-type Al _0.15 Ga _0.85 N having a thickness of 0.007 μm (7 nm). Carrier block layer 41, p-type guide layer 42 made of p-type GaN having a thickness of 0.10 μm (100 nm), p-type cladding layer made of p-type Al _0.04 Ga _0.96 N having a thickness of 0.55 μm (550 nm) 43, a p-type contact layer 44 made of p-type GaN having a thickness of 0.1 μm (100 nm) was sequentially formed.

As shown in FIG. 7, the active layer 30 is formed on the n-type guide layer 23 after forming a first barrier layer 31 made of In _0.02 Ga _0.98 N having a thickness of 15 nm on the first barrier layer 31. Two well layers 32 made of In _0.09 Ga _0.91 N having a thickness of 7.5 nm, and a second barrier layer 33 made of In _0.03 Ga _0.97 N having a thickness of 6 nm sandwiched between the two well layers 32 Formed. Then, the final barrier layer 34 (In _0.02 Ga _0.98 N layer) having a thickness of 15 nm as the uppermost layer was formed on the well layer 32. That is, in this embodiment, the active layer 30 is configured in a multiple quantum well structure including two quantum well layers (well layers 32).

As growth raw materials for the nitride semiconductor crystals constituting these nitride semiconductor layers, trimethylgallium ((CH ₃ ) ₃ Ga: TMGa), trimethylindium ((CH ₃ ) ₃ In: TMIn) are used as group III element raw materials. ) And trimethylaluminum ((CH ₃ ) ₃ Al: TMAl), and ammonia (NH ₃ ) was used as a Group V element material. As a doping element which is an impurity for conductivity control, n-type is Si, a raw material is silane (SiH ₄ ), p-type is Mg, and a raw material is cyclopentadienylmagnesium (CP ₂ Mg). Doping amount is, n-type GaN layer 21 and the n-type cladding layer 22 is 4 × 10 ¹⁸ cm ^-3, n-type guide layer 23 is 1 × 10 ¹⁸ cm ^-3, the carrier blocking layer 41 is 1 × 10 ¹⁹ cm ^-3 The p-type guide layer 42, the p-type cladding layer 43, and the p-type contact layer 44 are all 5 × 10 ¹⁸ cm ⁻³ . The active layer was not intentionally doped.

  The growth temperatures are 1025 ° C. for the n-type nitride semiconductor layer 20, 780 ° C. for the active layer 30, and 1075 ° C. for the p-type nitride semiconductor layer 40.

  Further, the ridge stripe portion 55 shown in FIG. 6 was formed by using an ICP (Inductively Coupled Plasma) dry etching method using photolithography. The width of the ridge stripe portion 55 was 1.7 μm. The ridge stripe portion 55 was formed to extend in the [1-100] direction.

Subsequently, an insulating film 60 was formed on the p-type nitride semiconductor layer 40. The insulating film 60 has a two-layer structure of SiO ₂ / TiO ₂ (SiO ₂ is on the p-type nitride semiconductor layer 40 side). The layer thickness is 170 nm / 50 nm. For film formation, EB (Electron Beam) vapor deposition was used. After the film formation, an insulating film 60 having a predetermined pattern was obtained using a photolithography technique or the like.

  Next, a p-side electrode 70 having a stacked structure of Pd / Mo / Au (Pd is the insulating film 60 side) was formed on the insulating film 60. The layer thickness of the p-side electrode 70 is 50 nm / 15 nm / 200 nm. For film formation, EB (Electron Beam) vapor deposition was used. After the film formation, a p-side electrode 70 having a predetermined pattern was obtained using a photolithography technique or the like.

  At this time, the region where the p-side electrode 70 was not formed was periodically patterned so that the divided regions for region separation were formed in the [11-20] direction. The width of the divided area was 10 μm. Further, the pad electrode has a pattern as shown in FIG. 8 so that there are two regions per chip and wire bonding can be performed for each region. Of the laminated structure of the p-side electrode, Au mainly constitutes the pad electrode. The first pad electrode is electrically connected to the first region (p-side electrode 71), the second pad electrode is electrically connected to the second region (p-side electrode 72), and the L-shaped region therebetween is No electrode is formed, and this region corresponds to the divided region 95. The ridge stripe portion is indicated by a dotted line in the figure. When the bar is divided at a predetermined bar dividing position, the resonator length is 600 μm, and two patterns of 570 μm (first region) and 20 μm (second region) are provided therein. . Further, the p-side electrode 72 in the second region is short-circuited to the n-side electrode 80 by wire bonding described later, and the second region forms a short-circuited region.

  After the formation of the p-side electrode 70, the substrate 10 was polished using a grinding machine and a polishing machine so that the thickness (wafer thickness) was 120 μm. Thereafter, as the n-side electrode 80, Hf / Al / Mo / Pt / Au (Hf is the substrate side) was formed on the back surface of the substrate 10 by using the EB vapor deposition method. The layer thickness is 5 nm / 150 nm / 36 nm / 18 nm / 250 nm. Then, after forming the metal film (after forming the p-side electrode 70 and the n-side electrode 80), a good ohmic electrode was obtained by performing an annealing process at 500 ° C.

  Thereafter, the wafer was divided into bars in the direction parallel to the [11-20] direction by cleavage. As a result, a pair of opposed resonator end faces (end face 110 and end face 120) as shown in FIG. 1 were obtained. The crystal orientations of the end face 110 and the end face 120 are {1-100} planes. The bar division was performed so that the resonator length was 600 μm.

Subsequently, a coating film was formed on the end face of the resonator by using ECR sputtering. A coating film 200 made of AlON / Al ₂ O ₃ / SiO ₂ / Al ₂ O ₃ (AlON is on the end face 110 side) was formed on the end face 110. The layer thickness is 20 nm / 110 nm / 68 nm / 60 nm. The reflectance was 30% at 405 nm. A coating film 300 made of AlON / Al ₂ O ₃ / (SiO ₂ / TiO ₂ ) ₄ (AlON is on the end face 120 side) is formed on the end face 120 (note that “(SiO ₂ / TiO ₂ ) ₄ ” is “SiO 4 indicates that four layers having a structural unit of “ ₂ / TiO ₂ ” are stacked). The layer thickness is 20 nm / 110 nm / (68 nm / 44 nm) ₄ . The reflectivity was 95% at 405 nm.

  Subsequently, the nitride semiconductor laser element, which is the semiconductor laser element of this example, was obtained by dividing the chip so that the chip width was 400 μm.

  Then, the obtained nitride semiconductor laser element was mounted on a can package type semiconductor laser device. At this time, the first pad electrode (p-side electrode 71) is wire-bonded to the positive terminal of the stem, while the second pad electrode (p-side electrode 72) is connected to the negative terminal of the stem electrically connected to the n-side electrode. By wire bonding, the first region 91 becomes a gain region, and the second region 92 becomes a saturable absorption region having a short carrier lifetime. As a result, the saturable absorption region is arranged on the resonator end face (end face 120) side having a high reflectance.

  FIG. 9 shows the result of band calculation for the semiconductor laser device of this example. In this embodiment, no external bias voltage is applied. Further, since the active layer of this example is InGaN, spontaneous polarization was ignored as described above. In addition, each layer is assumed to have distortion by being aligned with the lattice constant of GaN. That is, the active layer made of InGaN is always subjected to compressive strain.

  The crystal orientation of the active layer of this example is inherited from the substrate, and the (000-1) plane is the upper surface. Therefore, a piezo electric field (second internal electric field) due to lattice distortion (strain due to lattice mismatch) is generated in the well layer of the active layer in the same direction as the first internal electric field due to the pn junction, which is shown in FIG. Thus, in the well layer, the band diagram is such that the n-type semiconductor layer side is lowered.

  On the other hand, as Comparative Example 1, except that the p-type semiconductor layer, the active layer, and the n-type semiconductor layer are all different from the semiconductor laser element of this embodiment only in that the (000 + 1) plane is the upper surface. A semiconductor laser device was fabricated in exactly the same manner as in this example, and band calculation was performed for this semiconductor laser device. The result is shown in FIG. Also in Comparative Example 1, no external bias voltage is applied.

  In the semiconductor laser device of Comparative Example 1, a piezo electric field having the same size and the opposite direction as that of the semiconductor laser device of this example is generated at the interface of each semiconductor layer. Therefore, a piezo electric field (second internal electric field) is generated in the well layer of the active layer of the semiconductor laser device of Comparative Example 1 in the direction opposite to the first internal electric field due to the pn junction.

  For this reason, as apparent from comparison between FIGS. 9 and 10, the semiconductor laser device of this example has a band in which the n-type semiconductor layer side is lowered in the well layer, whereas the comparative example 1 In the semiconductor laser element, the band is such that the n-type semiconductor layer side rises in the well layer.

  In the band diagram as in Comparative Example 1, carriers generated in the active layer (well layer) by light absorption are not easily swept out of the well layer.

  Incidentally, in the case of the comparative example 1, when a reverse bias voltage is applied, a band shape is formed such that the n-type semiconductor layer side is pulled down, and carriers are easily swept out as the reverse bias voltage increases. That is, in Comparative Example 1, self-excited oscillation was observed only after applying a reverse bias voltage of 5V. The presence or absence of self-excited oscillation can be performed with an optical oscilloscope.

  On the other hand, in this embodiment, even if no reverse bias voltage is applied, the well layer is in the form of a band in which the n-type semiconductor layer side is lowered, so that it occurs in the active layer (well layer) by light absorption. Carriers are quickly swept out of the well layer, and electrons are quickly diffused to the n-type semiconductor layer side and holes are diffused to the p-type semiconductor layer side by the action of the first internal electric field and the second internal electric field.

  Therefore, in this embodiment, the lifetime of carriers generated in the active layer can be shortened, whereas in the active layer of Comparative Example 1, it cannot be expected to shorten the carrier lifetime. As a result, the semiconductor laser device of this example easily exhibits self-excited oscillation characteristics (easily self-excited oscillation). In fact, in the semiconductor laser device of this example, self-oscillation was confirmed without applying a reverse bias voltage.

  As described above, the semiconductor laser device according to the present example shows an excellent effect because the separation electrode type as in the present invention (at least one of the p-side electrode and the n-side electrode intersects the longitudinal direction of the resonator). In the semiconductor laser device (which is electrically separated into two or more regions by the divided regions), the active layer has at least a part thereof (in the well layer in this embodiment), an n-type semiconductor layer and a p-type semiconductor layer. This is because a second internal electric field different from the first internal electric field (piezoelectric field due to lattice distortion in this embodiment) is generated in the same direction as the direction of the first internal electric field due to the pn junction. It is.

  In the present invention, a second internal electric field different from the first internal electric field is generated in the same direction as the direction of the first internal electric field due to the pn junction in the barrier layer among the active layers. Preferably it is. However, unlike the well layer, the barrier layer may generate a second internal electric field in a direction opposite to the direction of the first internal electric field. In FIG. 9, the piezo electric field (second internal electric field) is generated in a direction opposite to the direction generated in the well layer (that is, generated in the direction opposite to the first internal electric field). As a result, the second internal electric field is pn junction. Therefore, the internal electric field in the same direction as the well layer (the first internal electric field and the second internal electric field are canceled out) only when the first internal electric field is larger than the second internal electric field. The resulting internal electric field) will be in the barrier layer (FIG. 9 of this example shows this case).

  Therefore, when the active layer has a quantum well structure or a multiple quantum well structure, the effect of the present invention is the same direction as the direction of the first internal electric field due to the pn junction between the n-type semiconductor layer and the p-type semiconductor layer at least in the well layer. In addition, if a second internal electric field different from the first internal electric field is generated, it can be obtained.

  As long as the above points are satisfied, various modifications other than the structure of the semiconductor laser device of this embodiment can be made. For example, if an AlGaInP-based or AlGaAs-based semiconductor layer is formed on a GaAs {111} substrate as a semiconductor layer (active layer) instead of a nitride semiconductor layer, a piezoelectric field due to lattice mismatch is generated. Therefore, the effect of the present invention can be achieved.

  However, since the nitride semiconductor layer is characterized by a large band gap, the first internal electric field due to the pn junction is larger than that of other semiconductor systems. Therefore, the nitride semiconductor layer is more suitable for obtaining self-excited oscillation in the separation electrode type semiconductor laser element, and the effect of the present invention can be remarkably exhibited.

  In the present embodiment, the p-side electrode 72 and the n-side electrode 80 of the second region 92 that is a saturable absorption region are short-circuited, but it is not always necessary to be short-circuited. Since this short circuit is intended to shorten the carrier lifetime in the saturable absorption region, it is not necessary to perform a short circuit when self-excited oscillation can be obtained without a short circuit. In addition, depending on the growth conditions of the semiconductor layer, a part of the p-type semiconductor layer or the n-type semiconductor layer may be different from the crystal orientation of the active layer. However, the effect of the present invention is desired for the active layer. It can be obtained if it has a crystal orientation. Whether the upper surface of crystal growth is the (000 + 1) plane or the (000-1) plane should be confirmed by a technique such as CBED (convergent beam electron diffraction) method or CAICISS (CoAxial Impact Collision Ion Scattering Spectroscopy). Can do.

  Since the semiconductor laser device of this embodiment can achieve self-excited oscillation without applying a reverse bias voltage to the saturable absorption region, the system can be simplified and miniaturized when used as a BD light source (especially a reading light source). Is possible. In addition, since the self-excited oscillation occurs even if the saturable absorption region is reduced, it is possible to suppress a sudden rise in the optical output near the threshold current.

  Also, when the semiconductor laser device of the present embodiment is used in a semiconductor laser device that uses a light-induced current flowing in a saturable absorption region for laser light output detection, the light-induced current increases, so that the detection capability is improved.

  Further, not only for BD applications but also for display applications for displaying images, there is an effect of reducing speckle noise by entering a multi-wavelength mode oscillation state.

<Example 2>
The semiconductor laser device of this example is a nitride semiconductor laser device, which uses a p-type GaN substrate as the substrate 10, and the upper surface of the active layer 30 is a (000 + 1) plane as shown in FIG. The p-type nitride semiconductor layer 40 is located in the lower side of the layer 30, that is, in the [000-1] direction, and the n-type nitride semiconductor layer 20 is located in the [000 + 1] direction. The semiconductor laser device has the same structure as that of the semiconductor laser device of Example 1 except that the positional relationship between the 70 and the n-side electrode 80 is reversed upside down.

  Also in the semiconductor laser device of the present example, the well layer of the active layer has a piezoelectric field (second internal electric field) caused by lattice distortion (strain due to lattice mismatch) in the same direction as the direction of the first internal electric field due to the pn junction. ) Occurs. The results of the band calculation of the semiconductor laser device of this example are the same as those shown in FIG. 12 described later. Based on the structure (FIG. 9) in which the band calculation is performed in Example 1, the stacked structure of the semiconductor layers is shown. The calculation result is obtained when the image is turned upside down. Thus, it can be seen that the effects of the present invention can also be obtained by the laminated structure of the semiconductor layers such as the semiconductor laser element of this embodiment.

<Example 3>
This example relates to a nitride semiconductor laser element as a semiconductor laser element, and a schematic cross-sectional view of a cross section parallel to the end face is shown in FIG. 13 (the thickness of each layer is not accurately reflected).

  First, n-type GaN having an upper surface of (000 + 1) plane was used as the substrate 10. When a substrate made of p-type GaN is used as in the second embodiment, a desired nitride semiconductor laser device can be obtained by inverting the stacked structure of the semiconductor layer in the first embodiment. However, since it is difficult to obtain a substrate made of such p-type GaN, an n-type GaN substrate was used.

  As shown in FIG. 13, the p-type nitride semiconductor layer 40 includes a p-type cladding layer 43, a p-type guide layer 42, and a carrier block layer 41, and the n-type nitride semiconductor layer 20 has an n-type. The guide layer 23, the n-type cladding layer 22, and the n-type GaN layer 21 are included.

Specifically, a p-type cladding layer 43 made of p-type Al _0.04 Ga _0.96 N having a thickness of 1.0 μm (1000 nm) is formed on the substrate 10 by MOCVD, and a thickness of 0.10 μm (100 nm) is set. The p-type guide layer 42 made of p-type GaN, the carrier block layer 41 made of p-type Al _0.15 Ga _0.85 N having a thickness of 0.007 μm (7 nm), the active layer 30, and the thickness of 0.17 μm (170 nm). n-type guide layer 23 made of n-type GaN, n-type cladding layer 22 made of n-type Al _0.03 Ga _0.97 N having a thickness of 0.55 μm (550 nm), n-type GaN layer having a thickness of 0.1 μm (100 nm) 21 were formed sequentially.

As shown in FIG. 14, the active layer 30 is formed on the carrier blocking layer 41 after forming a first barrier layer 31 made of In _0.02 Ga _0.98 N having a thickness of 15 nm on the first barrier layer 31. Two well layers 32 made of In _0.09 Ga _0.91 N having a thickness of 7.5 nm and a second barrier layer 33 made of In _0.03 Ga _0.97 N having a thickness of 6 nm sandwiched between the two well layers 32 Formed. Then, the final barrier layer 34 (In _0.02 Ga _0.98 N layer) having a thickness of 15 nm as the uppermost layer was formed on the well layer 32. That is, in this example, as in Example 1, the active layer 30 was configured in a multiple quantum well structure including two quantum well layers (well layers 32).

As growth raw materials for the nitride semiconductor crystals constituting these nitride semiconductor layers, trimethylgallium ((CH ₃ ) ₃ Ga: TMGa), trimethylindium ((CH ₃ ) ₃ In: TMIn) are used as group III element raw materials. ) And trimethylaluminum ((CH ₃ ) ₃ Al: TMAl) were used. In addition, ammonia (NH ₃ ) was used as a group V element material. As a doping element which is an impurity for conductivity control, n-type is Si, a raw material is silane (SiH ₄ ), p-type is Mg, and a raw material is cyclopentadienylmagnesium (CP ₂ Mg). Doping amount is, n-type GaN layer 21, n-type cladding layer 22 is 4 × 10 ¹⁸ cm ^-3, n-type guide layer 23 is 1 × 10 ¹⁸ cm ^-3, the carrier blocking layer 41 is 1 × 10 ¹⁹ cm ^-3 The p-type cladding layer 43 and the p-type guide layer 42 are all 5 × 10 ¹⁸ cm ⁻³ .

In addition, the active layer was not intentionally doped.
The growth temperatures are 1075 ° C. for the p-type nitride semiconductor layer 40, 780 ° C. for the active layer 30, and 1025 ° C. for the n-type nitride semiconductor layer 20.

  Also, the ridge stripe portion 55 shown in FIG. 13 was formed using an ICP (Inductively Coupled Plasma) dry etching method using photolithography. Unlike Example 1, a part of n-type nitride semiconductor layer 20 was removed to form ridge stripe portion 55. The width of the ridge stripe portion 55 was 1.7 μm. The ridge stripe portion 55 was formed to extend in the [1-100] direction.

  Further, the insulating film 60 and the n-side electrode 80 were formed as shown in FIG. The insulating film 60 was made of the same material and structure as in Example 1 and formed in the same manner. The n-side electrode 80 was made of the same material and configuration as in Example 1, and formed at a position corresponding to the p-side electrode 70 in Example 1.

  On the other hand, since the p-side electrode 70 cannot be formed on the back surface of the substrate 10 in the same manner as in the first embodiment, the ICP is formed to a depth at which the p-type cladding layer 43 is exposed in a region where the ridge stripe portion 55 is not provided. The p-side electrode 70 was formed by digging using a dry etching method (removing each semiconductor layer) and contacting the exposed upper surface of the p-type cladding layer 43. The material and configuration of the p-side electrode 70 are the same as those in the first embodiment.

  Subsequently, the n-side electrode 80 was electrically separated into two regions by a divided region 95 intersecting with the longitudinal direction of the resonator. However, since the n-type nitride semiconductor layer 20 has a lower resistance than the p-type nitride semiconductor layer 40, it is difficult to electrically separate adjacent regions sufficiently only by separating the n-side electrode 80. Therefore, the n-type nitride semiconductor layer 20 at the position of the divided region 95 is dug (removed) to the upper part of the active layer by using the ICP dry etching method. This step was performed simultaneously with the formation of the ridge stripe portion 55.

  After that, the nitride semiconductor laser device of this example was obtained by performing substrate thinning, end face formation, coating film formation, chip division, mounting, and the like by the same method as in Example 1.

  When the band calculation is performed for the semiconductor laser device of this example, it is as shown in FIG. 12, and since the carrier is easily swept out from the well layer as in Example 1, the carrier lifetime of the saturable absorption region is as follows. Can be shortened. For this reason, the semiconductor laser device of this example is prone to self-oscillation, and self-oscillation was obtained without applying a reverse bias. Therefore, the semiconductor laser device of this example showed excellent effects as the semiconductor laser device of Example 1.

  The semiconductor laser device according to the embodiment of the present invention described above is not limited to the above-described example, and may have a configuration other than the above-described example.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  10 substrate, 20 n-type nitride semiconductor layer, 21 n-type GaN layer, 22 n-type cladding layer, 23 n-type guide layer, 30 active layer, 31 first barrier layer, 32 well layer, 33 second barrier layer, 34 Final barrier layer, 40 p-type nitride semiconductor layer, 41 carrier block layer, 42 p-type guide layer, 43 p-type cladding layer, 44 p-type contact layer, 55 ridge stripe portion, 60 insulating film, 70, 71, 72 p Side electrode, 80 n side electrode, 90 resonator, 91 first region, 92 second region, 95 divided region, 100 nitride semiconductor laser element, 110, 120 end face, 200, 300 coating film.

Claims (18)

At least an n-type semiconductor layer, an active layer, and a p-type semiconductor layer are stacked on the substrate,
An n-side electrode in contact with the n-type semiconductor layer or the substrate, a p-side electrode in contact with the p-type semiconductor layer or the substrate, and a resonator,
At least one of the p-side electrode and the n-side electrode is electrically separated into two or more regions by a divided region that intersects the longitudinal direction of the resonator,
At least a part of the active layer has a second kind of second electrode different from the first internal electric field in the same direction as the direction of the first internal electric field by the pn junction between the n-type semiconductor layer and the p-type semiconductor layer. A semiconductor laser element in which an internal electric field is generated.   The active layer has a quantum well structure or a multiple quantum well structure having one or a plurality of well layers and one or a plurality of barrier layers, and the n-type semiconductor layer and the p-type semiconductor in the well layer. 2. The semiconductor laser device according to claim 1, wherein a second internal electric field different from the first internal electric field is generated in the same direction as the direction of the first internal electric field due to a pn junction with the layer.   The semiconductor laser device according to claim 1, wherein the second internal electric field is a piezo electric field caused by lattice distortion. The active layer is composed of a nitride semiconductor crystal having a wurtzite crystal structure,
The n-type semiconductor layer is located in the [000 + 1] direction of the active layer,
The semiconductor laser device according to claim 1, wherein the p-type semiconductor layer is located in a [000-1] direction of the active layer.   5. The semiconductor laser device according to claim 1, wherein each of the n-type semiconductor layer and the p-type semiconductor layer is a nitride semiconductor layer.   6. The semiconductor laser device according to claim 5, wherein each of the nitride semiconductor layers is composed of a nitride semiconductor crystal having a wurtzite crystal structure.   The semiconductor laser device according to claim 1, wherein the substrate is a nitride semiconductor crystal.   The semiconductor laser device according to claim 7, wherein the nitride semiconductor crystal has a wurtzite crystal structure.   The semiconductor laser device according to claim 7, wherein the nitride semiconductor crystal is GaN.   The semiconductor laser device according to claim 1, wherein the active layer is InGaN subjected to compressive strain. The active layer has an upper surface of (000-1) plane,
The semiconductor laser device according to claim 4, wherein the p-type semiconductor layer is located in a [000-1] direction of the active layer. The active layer has an upper surface of (000 + 1) plane,
The semiconductor laser device according to claim 4, wherein the p-type semiconductor layer is located in a [000-1] direction of the active layer.   The semiconductor laser device according to claim 4, wherein the n-type semiconductor layer and the p-type semiconductor layer each have the same crystal orientation as that of the active layer.   The semiconductor laser device according to claim 8, wherein the substrate has the same crystal orientation as that of the active layer.   The semiconductor laser device according to claim 1, wherein the semiconductor laser device has self-oscillation characteristics.   At least one region of electrodes separated by the divided region is short-circuited with an electrode on the opposite side of the electrode to form a short-circuit region, and at least one region of electrodes other than the short-circuited electrode is 2. The semiconductor laser device according to claim 1, wherein a non-short-circuit region that is not short-circuited with an electrode opposite to the electrode is formed.   An optical disk apparatus using the semiconductor laser element according to claim 1 as a light source.   An image display device using the semiconductor laser element according to claim 1.

Images