JP4529372B2 - Semiconductor laser element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device in which a dielectric protective film is formed on an end face of a semiconductor layer using a nitride semiconductor, and more particularly to a high-power semiconductor laser device. Specific examples of the composition of the semiconductor element include GaN, AlN, InN, or III-V group nitride semiconductors containing AlGaN, InGaN, and AlInGaN, which are mixed crystals thereof.
[0002]
[Prior art]
A nitride semiconductor device has a light emission in a wide wavelength region from a relatively short wavelength ultraviolet region to a visible light region including red, and is a material constituting a semiconductor laser diode (LD) or a light emitting diode (LED). Is widely used. In recent years, miniaturization, long life, high reliability, and high output have progressed, and they are mainly used for electronic devices such as personal computers and DVDs, medical devices, processing devices, and light sources for optical fiber communication.
[0003]
Such a nitride semiconductor device mainly includes a buffer layer, an n-type contact layer, a crack prevention layer, an n-type cladding layer, an n-type light guide layer, an active layer, a p-type electron confinement layer, and a p-type light guide on a sapphire substrate. A layered structure in which a layer, a p-type cladding layer, a p-type contact layer, and the like are sequentially stacked. A stripe-shaped waveguide region is formed by forming a stripe-shaped ridge by etching or forming a current confinement layer. Each of the n-type contact layer and the p-type contact layer is provided with an n-side electrode and a p-side electrode, and the active layer emits light when energized. Further, a resonator surface is formed on both end faces of the waveguide region with a predetermined resonator length, and laser light is emitted from this resonator surface.
[0004]
An insulating protective film or the like is formed on such a resonator surface, thereby providing a difference in reflectance between the emission side and the monitor side. Since the output of the protective film on the monitor side can be improved by providing a protective film having a high reflectance, a protective film having a relatively high reflectance as compared with the emission side is provided.
[0005]
Further, in a semiconductor laser element having a protective film having a large difference in reflectance between the monitor side and the emission side, light leaking from the waveguide region (stray light) is not easily emitted from the monitor side, and is emitted from the end surface on the emission side. become. Therefore, the stray light may cause noise (unevenness) in the far field pattern (FFP), resulting in a non-Gaussian distribution. In order to prevent these stray lights from being emitted to the outside, an opaque film made of a metal film or the like can be formed so as to cover the end face of the substrate.
[0006]
[Patent Document 1]
JP 2002-280663 A
[0007]
However, when a photodiode (detector) is provided on the monitor side to control the drive of the laser element, if the reflectance of the end face protective film is too high, the output of light emitted to the outside is too low. This makes it difficult for the detector to detect, and thus causes a problem that drive controllability is reduced and malfunction is likely to occur. Furthermore, if an opaque film is provided on a part of the end face of the emission-side resonance surface, it is necessary to increase the number of steps such as a mask formation step. In particular, when a wafer is divided into bars and an end face protective film is formed on the end face of the bar laser, it is difficult to form a mask with high positional accuracy. It is even more difficult to control. In particular, when a metal material is used as the opaque film, there is a problem that a short circuit may be caused if the controllability of position accuracy is low. In addition, if an opaque film is formed over a wide area, the adhesion between the opaque film and the semiconductor layer or other protective film may decrease depending on the material due to the difference in thermal expansion coefficient between the metal material and the semiconductor layer. Problems such as easy peeling off occur.
[0008]
Accordingly, the present invention provides a semiconductor laser device that forms an end face protective film without increasing the number of steps, suppresses a reduction in light output from the monitor side, and is unlikely to malfunction, and stray light emitted from the end face on the emission side. An object of the present invention is to provide a semiconductor laser device that suppresses the deterioration of FFP due to the above, can obtain good beam characteristics, and has little deterioration even when the device is driven.
[0009]
[Means for Solving the Problems]
In order to solve the above problem, a semiconductor laser device of the present invention includes a nitride semiconductor layer including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, and the nitride semiconductor layer has a striped waveguide region. And a semiconductor laser element having an end face including a resonator surface at the end of the waveguide region, and having an end face protective film continuous from the resonator face to the non-resonator face on the end face, And a thickness gradient region where the film thickness decreases on the non-resonator surface, and a maximum region of the transmittance difference of the end face is included in the thickness gradient region.
[0010]
One of the end face protective films can be set as the emission side and the other as the monitor side by controlling the transmittance and the refractive index. These can be controlled by selecting the material and film thickness of the end face protective film according to the emission wavelength and the refractive index of the semiconductor layer. At this time, it is efficiently desired by controlling the reflectance of the end face protective film formed on the resonator face which is the end face of the light emitting layer area including the active layer and the light guide layer and which is the end face of the waveguide area. Can be obtained. In the present application, an end face protective film is provided in the vicinity of the resonator face (including the same face and non-identical face) so that the film thickness is decreased. With such a configuration, the end face protective film set to a desired transmittance (reflectance) on the resonator surface becomes a film having a transmittance different from the set transmittance. As a result, since the end face protective film having optical characteristics different from that of the resonator surface can be obtained, a multifunctional end face protective film capable of controlling the optical characteristics of the laser beam while being a single continuous end face protective film is provided. can do. Note that the film thickness of the film thickness inclined region only needs to be formed so as to be entirely inclined. For example, it may have a region that is not partially inclined, or may be inclined in the opposite direction. You may have the part which is doing.
[0011]
In order to provide a difference in transmittance on the end face, it can also be obtained by partially forming an end face protective film. For this reason, the number of steps such as having a mask is increased, and the mask shape and mask formation position are controlled. If the property is poor, the reflectance of the end face protective film on the resonance surface may be easily deviated from the setting. In addition, if a mask is provided at a position that is considerably separated from the resonator region in consideration of the deviation of the mask position accuracy, the end face protective film on the resonator face can be formed with high accuracy, but the region where the end face protective film is not formed is a waveguide. Some distance from the area. Therefore, the effect of controlling and improving the optical characteristics of the waveguide region is reduced.
[0012]
Further, when a protective film is partially provided using photolithography, a protective film forming region and a non-forming region are formed, and the film thickness difference and the transmittance difference change at the same position. Although it is preferable to provide a difference in transmittance, if the film thickness difference is too large, the optical characteristics may be hindered by the stepped portion, and problems such as difficulty in controlling the optical characteristics tend to occur. Furthermore, since the stress difference is likely to increase, the protective film may be easily peeled off. As in the present application, the end face protective film is formed so as to have a uniform film thickness on the resonator face at the end of the waveguide region, and the film thickness is inclined so that the film thickness gradually decreases on the non-resonator face. By providing the inclined region, adverse effects due to stress can be reduced. In addition, the optical characteristics are efficiently controlled in a region relatively close to the waveguide by controlling the difference in transmittance in the film thickness gradient region so that the region having the maximum transmittance difference is present in the region. be able to.
[0013]
In the semiconductor laser device according to claim 2 of the present invention, the end face has a stepped portion protruding from the resonator surface, and the film thickness inclined region is provided between the stepped portion and the resonator surface. Features.
[0014]
By adopting such a configuration, it is possible to form a film thickness gradient region in a portion closer to the waveguide region with good controllability within a range of several microns. In particular, it can be made difficult to be affected by the warp and thickness of the substrate or the in-plane distribution of the thickness of the semiconductor layer. In addition, the function of the end face protective film can be set more finely, for example, a plurality of thickness gradient regions can be formed.
[0015]
Claims of the invention 4 The semiconductor laser device described in 1 is characterized in that the film thickness inclined region of the end face protective film is provided so as to be inclined in a direction substantially parallel to the stacked surface of the semiconductor layers.
[0016]
With such a configuration, it is possible to control the optical characteristics particularly in the direction perpendicular to the stacked surface of the semiconductor layers.
[0017]
Claims of the invention 5 The semiconductor laser device described in (1) is characterized in that the film thickness inclination region of the end face protective film is provided so as to incline about the waveguide region.
[0018]
By adopting such a configuration, it is possible to control optical characteristics particularly in the lateral direction (direction parallel to the laminated surface) between the waveguide regions.
[0019]
Claims of the invention 6 In the semiconductor laser device described in the item 1, the thickness gradient region of the end face protective film has a plurality of regions having a transmittance difference, and the maximum region of the transmittance difference near the boundary between the film thickness gradient region and the film thickness non-gradient region. It is characterized by having.
[0020]
In the present application, the end face protective film has a film thickness gradient region where the film thickness gradually decreases on the non-resonator surface, but the film thickness gradient does not coincide with the transmittance gradient. The transmittance does not gradually change according to the film thickness, but in the initial region of the film thickness gradient region, that is, in the vicinity of the boundary between the film thickness non-gradient region and the film thickness gradient region, A plurality of regions having a transmittance difference can be formed. As in the present application, by providing the maximum transmittance difference region in the vicinity of the boundary between the film thickness gradient region and the film thickness non-tilt region, it is possible to provide a region having a large transmittance difference in a region relatively close to the waveguide. Therefore, the multifunctional end face protective film can be used efficiently.
[0021]
Claims of the invention 7 The semiconductor laser device described in 1 is characterized in that the end face protective film has a higher transmittance in the film thickness gradient region than in the film thickness non-tilt region on the resonator surface.
[0022]
The end face protection film on the monitor side resonator surface improves the light extraction efficiency by lowering the transmittance. It can be. For this reason, in the non-film thickness region on the resonator surface, the region where the transmittance difference between the end surfaces is maximum, that is, the high transmittance within the thickness gradient region continuously provided with the end surface protective film having low transmittance. By having a ratio region, the resonator part maintains a high reflectivity and realizes an excellent reflectivity, while emitting light leaking from the waveguide with high transmittance in the vicinity to the outside and monitoring Since light can be emitted toward the detector provided on the side, drive control is easy and malfunctions can be reduced.
[0023]
Claims of the invention 8 The semiconductor laser device described in (1) is characterized in that the transmittance of the film thickness gradient region is lower than the transmittance of the film thickness non-tilt region on the resonator surface.
[0024]
Since the end face protective film on the emission side resonator surface has a higher transmittance than that on the monitor side, light leaking from the waveguide region (stray light) is easily emitted to the outside. By adopting the configuration as in the present application, the resonator portion can maintain a high transmittance, and a region with a low transmittance can be easily provided in the vicinity thereof, thereby suppressing stray light from being emitted to the outside. Thus, it is possible to obtain a good FFP in which the main beam is not uneven.
[0025]
Claims of the invention 9 The semiconductor laser device described in 1 is characterized in that the film thickness gradient region of the end face protective film is provided on the end face on the n-type semiconductor layer side.
[0026]
By providing in such a region, the maximum region of transmittance difference is closer to the region, so that the optical characteristics can be controlled efficiently.
[0027]
Claims of the invention 10 The semiconductor laser device described in 1 is characterized in that the film thickness gradient region of the end face protective film is provided on the end face of the substrate provided on the n-type semiconductor layer side.
[0028]
By adopting such a configuration, it is possible to efficiently control the light emitted outside from the waveguide region in the manufacturing process.
[0029]
According to a fourteenth aspect of the present invention, there is provided a method for manufacturing a semiconductor laser device comprising: an exposed resonator of a bar-shaped laser device comprising a nitride semiconductor layer comprising an n-type semiconductor layer, an active layer, and a p-type semiconductor layer. A method of forming an end face protective film on an end face including a surface, When forming the end face protective film in a state where the laser element is sandwiched using a spacer having a protrusion, the protrusion is separated from the end face and extends to a part of the end face. By forming the end face protective film on the end face protective film, the film thickness non-inclined region on the end face protective film, the film thickness inclined region in which the film thickness decreases on the non-resonator surface, and the film thickness inclined region And forming a region having a maximum transmittance difference between the non-gradient film thickness region and the gradient film thickness region. It is characterized by that.
[0030]
With such a configuration, it is possible to easily form the film thickness uniform region (film thickness non-tilt region) and the film thickness tilt region without forming a mask in a separate process.
[0031]
The present invention Pertaining to In the method of manufacturing a semiconductor laser element, the protruding portion of the spacer is provided so as to protrude so as to be substantially parallel to the stacked surface of the semiconductor layer end surface. May be .
[0032]
With such a configuration, it is possible to form a thickness gradient region substantially parallel to the stacked surface of the semiconductor layers.
[0033]
The present invention Pertaining to In the semiconductor laser device manufacturing method, the protruding portion of the spacer is provided so as to protrude on the active layer in the region sandwiched between the waveguide regions on the end face of the semiconductor layer. May be .
[0034]
By setting it as such a structure, a film thickness inclination area | region can be formed in area | regions other than the resonator surface which is an end surface of a waveguide area | region.
[0035]
The present invention Pertaining to In the semiconductor laser device manufacturing method, the protrusion of the spacer is formed in one direction of the spacer. May .
[0036]
With such a configuration, the film thickness gradient region can be formed only on the p-type semiconductor layer side or the n-type semiconductor layer side of the end face of the bar-shaped laser.
[0037]
The present invention Pertaining to In the method of manufacturing a semiconductor laser device, the spacer has a recess between a flat surface facing the semiconductor layer and a protruding portion protruding from the flat surface. May be .
[0038]
By adopting such a configuration, the controllability of the mounting position of the bar-shaped laser can be improved.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described, but the semiconductor laser element of the present invention is not limited to the element structure shown in the embodiment.
[0040]
The semiconductor laser device of the present invention includes an end face protective film provided on an end face of a semiconductor layer having a stripe-shaped waveguide region, a uniform film thickness region (film thickness non-gradient region), a film thickness gradient region, Are respectively located at specific positions. Thereby, it can be set as the structure which has the maximum area | region of the transmittance | permeability difference of an end surface in a film thickness inclination area | region. Since the non-gradient film thickness region and the gradient film thickness region are formed in the same process, an end face protective film with excellent adhesion can be formed without increasing other processes such as a mask formation process, and the optical characteristics are controlled. Possible end faces can be easily formed. The design of the film thickness is determined on the basis of the transmittance (reflectance) at the resonator surface, which is the end face of the light emitting layer region including the active layer, on both the emission side and the monitor side.
[0041]
Both the emission side and the monitor side can be designed values according to the purpose.
The monitor side is mainly set so that the transmittance is low. An example in which the transmittance of the resonator surface is low is shown in FIG. In FIG. 2, a p-side ohmic electrode 205 is formed on a semiconductor layer in which an n-type semiconductor layer 202, an active layer 204, and a p-type semiconductor layer 203 are stacked on a substrate 201, and a p-side pad electrode 206 is further formed thereon. It is sectional drawing of the waveguide area | region of a semiconductor layer. An end surface protective film 211 is formed so as to be continuous with a resonator surface that is an end surface of the waveguide region and a non-resonator surface that is an end surface other than the waveguide region. The end face protective film 211 is designed such that the transmittance is low in the region including the resonator surface, and the maximum region of the transmittance difference is formed in the thickness gradient region as shown in the figure. ing. Thereby, even if it is a monitor side end face protective film in which light is not easily emitted to the outside, the controllability of the detector due to insufficient output can be made difficult to deteriorate due to the light emitted from the thickness gradient region. Here, the transmittance of the film thickness gradient region is designed to be higher than the transmittance of the end face of the substrate 201, but the substrate can also be set to have the highest transmittance.
[0042]
Further, the transmittance is mainly set on the exit-side resonator surface so that the transmittance is high. An example of the case where the transmittance of the resonator surface is high is shown in FIG. FIG. 3 illustrates a semiconductor layer in which a p-side ohmic electrode 305 and a p-side pad electrode 306 are formed on a semiconductor layer in which an n-type semiconductor layer 302, an active layer 304, and a p-type semiconductor layer 303 are stacked on a substrate 301. It is sectional drawing of a waveguide area | region. An end face protective film 311 is formed so as to be continuous with a resonator surface that is an end face of the waveguide region and a non-resonator surface that is an end face other than the waveguide region. The end face protective film 311 is designed so that the transmittance is high in the region including the resonator surface, and the maximum region of the transmittance difference is formed in the thickness gradient region as shown in the figure. ing. Thereby, even if it is an exit side end face protective film that easily emits light, it is possible to prevent light from leaking outside from the waveguide region due to the low transmittance of the film thickness gradient region. It is possible to obtain a good FFP by reducing the deterioration of FFP due to noise caused by leaked light (stray light).
[0043]
The region where the transmittance difference is provided is preferably a position relatively close to the waveguide region, which makes it easier to control the optical characteristics. Further, the change rate of the transmittance difference may be gradually changed or may be rapidly changed. When the end face protection film is a multilayer film, the rate of change varies depending on the number of stacked films (number of pairs), the thickness of each layer, and the refractive index of the material used. can do.
[0044]
FIG. 4 is a diagram in which the end face protective film formed on the resonator surface is designed to have low transmittance. As in FIG. 2, an end face protective film having a single layer or a small number of layers (a small number of pairs) is formed. Therefore, the change in transmittance is relatively gradual compared to FIG.
[0045]
Also, the area of the film thickness gradient region can be arbitrarily selected. For example, when FIG. 2 and FIG. 4 are end face protective films having the same number of layers, the manner of change is almost the same in the region where the transmittance difference is maximum. However, the amplitude region (number of amplitudes) of the subsequent transmittance curve is different. Such a difference can be adjusted by the sputtering conditions and angle at the time of forming the end face.
[0046]
In the present application, the transmittance of the end face protective film is a transmittance with respect to a wavelength emitted from the active layer. Further, the end face protective films that are made of the same material and are continuously provided are areas where the film thickness is uniform between the waveguide area and the end faces of the other areas, that is, the resonator face and the non-resonator face. And by setting it as the film thickness inclination area | region where a film thickness reduces gradually, it can be set as the optical multifunctional film from which the transmittance | permeability with respect to light emission wavelength differs.
[0047]
In addition, the end face protective film may have a laminated structure of the end face protective film having the above-described thickness gradient region and the end face protective film having a substantially uniform film thickness. In FIG. 5, an end face protective film 511 (b) is formed continuously over the substrate 501 and part of the n-type semiconductor layer. Here, the film thickness non-inclined region is provided only on the end surface of the substrate, and the transmittance is set to be low. And it has the maximum area | region of the transmittance | permeability difference in a film thickness inclination area | region, and has an area | region where the transmittance | permeability becomes the maximum here. Then, the end face protective film 511 (a) is formed on such an end face protective film and on a part of the n-type semiconductor layer 502 not covered with the end face protective film 511 (b), the active layer 504, and the end face of the p-type semiconductor layer. ) Is formed. The end face protective film 511 (a) covers the entire end face. Thus, it can also be set as a composite end surface protective film. Which of these composite end face protective films is laminated may be appropriately selected depending on the purpose and application. Also, an end face protective film having a film thickness gradient region on the p-type semiconductor layer side and an end surface protective film having a film thickness gradient region on the n-type semiconductor layer side can be laminated. Alternatively, end face protective films having end face inclined regions having the same inclination direction of the respective film thickness inclined regions can be laminated so that the regions (areas) thereof are different.
[0048]
By providing the film thickness gradient area only on the monitor side end face or only on the output side end face, it functions as an end face protective film with excellent characteristics. However, it is preferable to provide it on both end faces to achieve high output. However, it is possible to obtain a semiconductor laser device having extremely good device characteristics with few malfunctions and noise.
[0049]
Specific materials for the end face protective film include Si, Mg, Al, Hf, Nb, Zr, Sc, Ta, Ga, Zn, Y, B, Ti, and oxides, nitrides thereof as conductor materials. A material selected from any one selected from compounds such as fluorinated compounds and fluorides can be used. These may be used alone, or may be used as a compound or a multilayer film in which a plurality of them are combined. Preferred materials are materials using Si, Mg, Al, Hf, Zr, Y, and Ga. Moreover, AlN, AlGaN, BN, etc. can be used as a semiconductor material. As the insulator material, compounds such as Si, Mg, Al, Hf, Nb, Zr, Sc, Ta, Ga, Zn, Y, and B oxides, nitrides, fluorides, and the like can be used.
[0050]
Embodiment 1
FIG. 1 shows the structure of a nitride semiconductor device according to the first embodiment of the present invention. An n-type nitride semiconductor layer 102, an active layer 104, and a p-type nitride semiconductor layer 103 are formed on a substrate 101. Are stacked, and a p-type nitride semiconductor layer is provided with a striped ridge. The ridge can be formed by removing a part of the p-type nitride semiconductor layer by means such as etching, whereby an effective refractive index type waveguide can be formed. The ridge may be formed by etching a part from the p-type nitride semiconductor layer to the n-type nitride semiconductor layer to form a complete refractive index type waveguide, or the ridge is formed by selective growth. May be. The ridge is not limited to the forward mesa shape whose width on the bottom side is large and the stripe width decreases as it approaches the top surface. Conversely, the reverse mesa shape that the stripe width decreases as it approaches the ridge bottom surface may be used. It may be a stripe having various side surfaces or a shape in which these are combined. Also, the striped waveguides need not have the same width. Alternatively, a buried laser element in which a semiconductor layer is regrown on the ridge surface or both sides of the ridge after such a ridge is formed may be used. Further, it may be a gain waveguide type waveguide having no ridge.
[0051]
A first insulating film 109 is formed from the side surface of the ridge and the upper surface of the continuous p-type nitride semiconductor layer from the ridge. A p-side ohmic electrode 105 is provided on the top surface of the ridge and the first insulating film, and an n-side ohmic electrode 107 is provided on the top surface of the n-type nitride semiconductor layer. A second insulating film 110 having an opening above the n-side ohmic electrode is provided so as to continue to the top of the first insulating film. A p-side pad electrode 106 in contact with the second insulating film and the p-side ohmic electrode is provided on the p-type nitride semiconductor layer. An n-side pad electrode 108 is also provided on the n-side ohmic electrode.
[0052]
Since the functions of the ohmic electrode and the pad electrode are different, the size (width / length) and shape of each of the ohmic electrode and the pad electrode can be changed according to the purpose or in consideration of the process. Further, since it is only necessary to be formed so as to be in contact with the operating portion, it is not necessary to connect the entire surface of each. In the case of the p-side electrode, it is preferable to join at the top of the ridge so as to correspond to the waveguide region, for example, since an increase in operating voltage due to interface resistance can be suppressed. In addition, the pad electrode formed in a later process than the ohmic electrode can be formed so as to be in contact with only the ohmic electrode on the bottom surface, or a part of the pad electrode is formed on the ohmic electrode and the other part is formed. It may be provided so as to be in contact with the semiconductor layer or the insulating film.
[0053]
The ohmic electrode is preferably formed in a stripe shape so as to be substantially parallel to the stripe-shaped waveguide region, but is not limited thereto. That is, even if the shape of the ohmic electrode is not a stripe shape, the contact region with the semiconductor layer may be formed in a stripe shape. In addition, it is preferable to provide the entire waveguide region in the direction parallel to the stripe, but the photolithography process at the time of electrode formation should be separated from the end face in consideration of the chip forming process in the subsequent process. The preferred size and shape can be selected according to the purpose.
[0054]
The connection region between the ohmic electrode and the pad electrode is preferably connected to a region corresponding to the entire region of the waveguide region, so that the operating voltage can be stabilized. However, the pad electrode is made shorter than the ohmic electrode, Is preferably not formed on the upper part of the divided region during element division.
[0055]
As an electrode material of the p-side ohmic electrode provided in the p-type nitride semiconductor layer, a material having high ohmic properties and adhesion with the p-type nitride semiconductor layer can be selected. Specifically, Ni, Co, Fe, Cr, Al, Cu, Au, W, Mo, Ta, Ag, Pt, Pd, Rh, Ir, Ru, Os and their oxides, nitrides, etc., and these single layers, alloys, or A multilayer film can be used. Preferably, at least one selected from Ni, Co, Fe, Cu, Au, and Al, and oxides, nitrides, and the like thereof.
[0056]
The p-side ohmic electrode can realize good ohmic properties by heat treatment. As heat processing temperature, it is preferable to set it as the temperature range of 350 to 1200 degreeC, More preferably, it is 400 to 750 degreeC, Most preferably, it is 450 to 600 degreeC.
[0057]
As electrode materials for the p-side pad electrode, Ni, Co, Fe, Ti, Cu, Au, W, Zr, Mo, Ta, Ag, Pt, Pd, Rh, Ir, Ru, Os and oxides thereof Nitrides, etc., and these single layers, alloys, or multilayer films can be used. Since the uppermost layer connects wires and the like, it is preferable to use Au. In order to prevent this Au from diffusing, a material having a relatively high melting point that functions as a diffusion preventing layer is preferably used for the lower layer. For example, Ti, Pt, W, Ta, Mo, TiN, etc. are mentioned, and Ti is mentioned as a particularly preferable material. As the film thickness, the total film thickness is preferably 3,000 to 20,000 mm, more preferably 7000 to 13,000 mm.
[0058]
As the n-side ohmic electrode provided on the n-type nitride semiconductor layer, a material having high ohmic properties and adhesion to the n-type nitride semiconductor layer can be selected. Specifically, Ni, Co, Fe, Ti Cu, Au, W, Zr, Mo, Ta, Al, Ag, Pt, Pd, Rh, Ir, Ru, Os, and the like. These single layers, alloys, or multilayer films can be used. A multilayer structure in which Ti and Al are sequentially laminated is preferable. After forming the n-side ohmic electrode, it may be preferable to perform heat treatment depending on the material in order to improve the ohmic property with the semiconductor layer. Further, the film thickness of the n-side ohmic electrode is preferably about 100 to 30000 mm, more preferably about 3000 to 15000 mm, and particularly preferably 5000 to 10,000 mm. Forming within this range is preferable because it can be an electrode with low contact resistance.
[0059]
Examples of the electrode material for the n-side pad electrode include Ni, Co, Fe, Ti, Cu, Au, W, Zr, Mo, Ta, Al, Ag, Pt, Pd, Rh, Ir, Ru, and Os. These single layers, alloys, or multilayer films can be used. Preferably, a multilayer film is used, and Au is preferably used because the uppermost layer connects wires and the like. In order to prevent this Au from diffusing, a material having a relatively high melting point that functions as a diffusion preventing layer is preferably used for the lower layer. For example, Ti, Pt, W, Mo, TiN, etc. are mentioned. As the film thickness, the total film thickness is preferably 3,000 to 20,000 mm, more preferably 7000 to 13,000 mm.
[0060]
The n-side electrode is not provided with an ohmic electrode and a pad electrode in separate steps as described above, but is formed continuously to serve both functions, that is, an ohmic electrode in ohmic contact with the semiconductor layer, and An n-electrode that also serves as a take-out electrode (pad electrode) for forming a wire may be used. This is relatively easy to make ohmic contact with the n-type semiconductor layer as compared with the p-side electrode, and is a region slightly separated from the waveguide region, so that it is not necessary to consider the optical characteristics so much. This is because of the large degree of freedom. The film thickness of such an n-electrode is preferably 3000 to 20000 mm as the total film thickness, more preferably 7000 to 13000 mm.
[0061]
The first insulating film is provided to limit the current injection region to the upper surface of the ridge. However, since the first insulating film is provided close to the waveguide region, it also acts on the light confinement efficiency. Therefore, a preferable film thickness can be selected depending on the insulating film material to be used. The first insulating film can also be formed to have substantially the same width as the nitride semiconductor layer. The first insulating film formed before the p-side ohmic electrode is heat-treated together when the ohmic electrode is heat-treated. By performing the heat treatment, the strength of the film (bonding force at the atomic level in the film) is increased as compared with the deposited film, and the bonding strength at the interface with the semiconductor layer is also improved. By forming such a first insulating film up to the end portion of the upper surface of the semiconductor layer on which the second insulating film is formed, the adhesion of the second insulating film can also be improved.
[0062]
In addition, the p-side pad electrode is not limited to the shape shown in FIG. 1B, and can be formed so as not to contact the second insulating film. In particular, when used in junction down, heat is applied to the p-side pad electrode, but at that time, the volume increases due to thermal expansion, and it tends to flow out in the side surface direction of the element (end direction of the p-type semiconductor layer). Moreover, since not only heat but also pressure is applied, the electrode material easily flows out in the lateral direction. Therefore, by separating from the second insulating film, it is possible to prevent the electrode material of the p-side pad electrode from flowing out in the side surface direction and causing a short circuit.
[0063]
The material of the first insulating film is an oxide, SiN, BN, SiC, AlN, or AlGaN containing at least one element selected from the group consisting of Si, Ti, V, Zr, Nb, Hf, and Ta. It is desirable to use at least one kind, and among them, it is particularly preferable to use an oxide of Zr, Hf, Si, BN, AlN, or AlGaN.
[0064]
The film thickness of the first insulating film is specifically in the range of 10 to 10,000 mm, preferably in the range of 100 to 5,000 mm. This is because if the thickness is 10 mm or less, it is difficult to ensure sufficient insulation at the time of electrode formation. If the thickness is 10,000 mm or more, the uniformity of the protective film is lost, and a good insulating film is not obtained. . Moreover, by being in the preferred range, a uniform film having a good refractive index difference between the ridge and the ridge can be formed on the side surface of the ridge.
[0065]
The second insulating film can be provided on the entire surface of the p-side ohmic electrode except for the upper portion of the ridge, and is preferably provided so as to continue to the side end faces of the p-type semiconductor layer and the active layer exposed by etching. . A preferable material is an oxide containing at least one element selected from the group consisting of Si, Ti, V, Zr, Nb, Hf, and Ta, and formed of at least one of SiN, BN, SiC, AlN, and AlGaN. Among them, SiO 2 is particularly preferable as SiO 2 ₂ , Al ₂ O ₃ , ZrO ₂ TiO ₂ And a single layer film or a multilayer film.
[0066]
Further, in order to set the stripe direction of the ridge as the resonator direction, the pair of resonator surfaces provided on the end face can be formed by cleavage or etching. In the case of forming by cleavage, it is preferable that the substrate and the semiconductor layer have cleavage properties, and an excellent mirror surface can be easily obtained by utilizing the cleavage properties. Further, even if there is no cleavage, the resonator surface can be formed by etching, and in this case, it can be obtained with a small number of steps by carrying out simultaneously when exposing the n electrode formation surface. It can also be formed simultaneously with the ridge formation. In this way, the number of steps can be reduced by forming each step simultaneously. However, in order to obtain a more excellent resonator surface, it is preferable to provide another step.
[0067]
In the present invention, the end face protective film has a film thickness gradient region. In the first embodiment, the end face protective film is provided on the monitor-side resonator surface. Specifically, as shown in FIG. The resonator surface at the end of the waveguide region and the non-resonator surface are formed to be a single plane. The end face protective film is formed so as to have a substantially uniform film thickness on the resonator surface, and has a film thickness gradient region formed so that the film thickness decreases on the non-resonator surface.
[0068]
The film thickness gradient region may be provided on almost the entire surface other than the resonator surface, or may be provided on a part thereof. In the first embodiment, the substrate is formed so that a part of the substrate is exposed. However, the present invention is not limited to such a configuration, and an end face protective film can be formed on almost the entire surface.
[0069]
In the first embodiment, the film thickness is inclined in a direction substantially parallel to the semiconductor layer. Such an end face protective film can be easily formed by using a spacer having a protruding portion as shown in FIGS. 6 (a) and 6 (b).
[0070]
In FIG. 6A, a bar-shaped laser element obtained by dividing a wafer on which a semiconductor layer is stacked and an electrode and the like are formed so that a resonator surface is exposed is installed in an apparatus such as a sputtering apparatus. It is a schematic diagram which shows this. The spacer 612 having the protruding portion 612 (a) is placed so as to sandwich the bar-shaped laser element. In the first embodiment, the substrate 601 side of the bar-shaped laser element faces the protruding portion. It is installed in. The protrusion 612 (a) of the spacer 612 has a width and thickness of the film thickness gradient region depending on the length and thickness of the protrusion, the shape and angle of the tip of the protrusion, and the distance between the resonator surface and the protrusion. The inclination rate can be changed.
[0071]
The width of the film thickness gradient region can be selected arbitrarily by controlling the distance between the protrusion and the resonator surface of the semiconductor layer and the width of the protrusion. When the dielectric multilayer film is formed with a plurality of pairs on the monitor side, the resonator surface at the end of the waveguide region is formed to have a uniform film thickness and low transmittance (high reflectance). Then, by using a spacer such that the protruding portion protrudes from the n-type semiconductor layer side (substrate side), a film thickness gradient region can be formed on the end surface of the n-type semiconductor layer.
[0072]
Moreover, as shown in FIG. 6, the spacer is preferably one in which the protruding portion 612 (a) is formed in one direction. In the case where the film thickness is controlled by the protruding portion, if the protruding portion is formed in both directions, the controllability of the film thickness tends to be lowered. In particular, since it is difficult to control the non-gradient region of the film thickness, that is, the uniform film thickness region, it is difficult to set the end face protective film, and it is difficult to form a desired reflectance (transmittance) with good reproducibility.
[0073]
In addition, the spacer may have a recess 612 (b) between a plane facing the semiconductor layer and a protrusion 612 (a) protruding from the plane. This is due to the workability of the spacer. In order to control the film thickness gradient region, for example, as shown in FIG. 6B, the surface of the substrate 601 and the surface of the spacer 612 are placed so that there is no gap. It is preferable to do this. In the case where the recess 612 (b) is not formed, this is likely to be a curved surface, and the curved surface protrudes from the flat portion, so that the substrate and the spacer cannot be placed with good adhesion. As a result, the region covered by the protruding portion is also deviated from the design value. As a result, the formation position accuracy of the film formation region is lowered, which is not preferable.
[0074]
In FIG. 7, as in FIG. 6, a spacer 712 having a protruding portion 712 (a) having a linear tip shape substantially parallel to the stacked surface of the semiconductor layers is used. 7A and 7B show the state of forming the end face protective film depending on the length of the protruding portion 712 (a). A film thickness gradient region 711 (b) is formed in a region not covered with the protruding portion 712 (a), and a film thickness non-tilt region is formed in the waveguide region including the active layer. Both of these regions can be changed according to the size of the protrusion 712 (a).
[0075]
In order to provide the film thickness gradient region, a spacer having a protruding portion is used as described above, or a semiconductor layer having a stepped portion protruding from the resonator surface on the end surface which is a film forming surface is used. Can do.
[0076]
Embodiment 2
In the second embodiment, as shown in FIG. 8, the film thickness gradient region is provided so as to be inclined with respect to the waveguide region, not in a direction parallel to the stacked surface of the semiconductor layers. By setting it as such a form, the light currently spreading in the horizontal direction of the light emitting layer containing an active layer can also be controlled. In the case of forming such an end face protective film, it can be easily formed by using a spacer as shown in FIG.
[0077]
In FIG. 8, a spacer 812 having a protruding portion 812 (a) having a tip shape that opens around the waveguide region of the semiconductor layer is used. FIGS. 8B and 8C show the state of the end face protective film formed using such a spacer. In this way, by forming the thickness gradient region so as to cover the active layer other than the waveguide region, for example, in the lateral direction due to the refractive index difference due to the ridge as in the semiconductor laser element having the waveguide having the ridge. In the case of a semiconductor laser device having a form in which light is effectively confined, the active layer is formed over the waveguide region and the region other than the waveguide. Easily released to the outside. In such a case, as shown in FIGS. 8B and 8C, the end face protective film on the emission side is formed in a shape that is not parallel to the laminated surface, and a film thickness gradient region is formed on the resonator surface. By setting a high transmittance in the non-gradient film thickness region and forming a region having a lower transmittance in the slope region around the film thickness, light can be emitted from outside the waveguide region. A function as a light-shielding film can be reduced.
[0078]
As the spacers shown in the first and second embodiments, it is not necessary to use the same spacers on the emission side and the monitor side. Therefore, the emission side has a film thickness inclined region inclined about the waveguide region. As an end face protective film, it is possible to suppress stray light from being emitted to the outside, and to have a good FFP in both the horizontal and vertical directions, and a film thickness inclined region that is inclined in a direction parallel to the laminated surface on the monitor side. The end face protective film can be driven with good controllability.
[0079]
Embodiment 3
In Embodiment 3, as shown in FIG. 9, a bar-shaped laser element having a stepped portion 913 on the end face of the semiconductor layer is used. As shown in FIG. 9, the end face of the light emitting region including the active layer is a single face (resonator face), and if there is a part of the n-type semiconductor layer or the substrate, the end face of the substrate is the resonator face. The shape is more protruding. Such a shape can be obtained by forming a resonator surface by RIE and then dividing the exposed n-type semiconductor layer or the exposed surface of the substrate into a bar shape. Here, by adjusting the length of the portion protruding from the resonator surface, the uniform film thickness region and the thick film gradient region of the end face protective film can be formed with good controllability. In FIG. 9, the stepped portion 913 includes a stepped portion 913 (a) composed of an n-type semiconductor layer 902 projecting from the resonator surface and a stepped portion composed of a substrate projecting further from the stepped portion of the n-type semiconductor layer. Although there are two step portions 913 (b), the present invention is not limited to such a configuration, and there may be only one step portion or two or more step portions.
[0080]
By providing the stepped portion, it is possible to provide a film thickness gradient region with high positional accuracy in a region closer to the resonator surface. In particular, when a semiconductor layer is formed using a heterogeneous substrate, the bar-shaped laser has a warp, so there is a limit to the control of the positional relationship between the protruding portion of the spacer and the end surface protective film formation region. There is. In addition, the film thickness of the semiconductor layer may be slightly different even with the same bar-shaped laser due to not only the warpage but also the in-plane distribution during the growth of the semiconductor layer. In such a case, since the step portion is provided in the semiconductor layer, control can be performed in a fine region that cannot be controlled by the spacer. Further, by providing a plurality of step portions, it is possible to form end face protective films having different optical characteristics in a single film formation step.
[0081]
In FIG. 9A, an end face protective film having a low transmittance is provided on the resonator surface, and a film thickness gradient region having a high transmittance is provided in the same plane, which is mainly used as an end face protective film on the monitor side. It is a figure which shows the form which can be done. Little light is emitted to the outside from the non-tilted region of the end face protection film on the resonator surface, and light with an output that can be detected by the detector is emitted from the tilted region on the resonator surface. be able to. The stepped portion 913 (a) is also provided with an end face protective film having a low transmittance, so that it is possible to suppress excessive emission of light. Thus, the film thickness non-gradient region and the film thickness gradient region can be arbitrarily selected. In FIG. 9B, the transmittance of the non-gradient region on the resonator surface is increased, and by providing a step in the semiconductor layer itself, the purpose and application, characteristics of the semiconductor layer itself, etc. In some cases, the function of the film thickness gradient region can be used more effectively.
[0082]
As described above, the end face protective film is formed by using a spacer having a protruding portion or a bar-shaped laser having a stepped portion protruding from the resonator and the surface of the semiconductor layer (including the substrate). By using a film thickness control means capable of partially controlling the film thickness between the film region and the target of the film forming material raw material, the end face protective film of the present invention can be easily formed.
[0083]
Further, by forming the end face protective film using the film thickness control means as in the present application, the upper surface or the lower surface of the semiconductor layer, that is, the upper surface (front surface) of the p-type semiconductor layer, the lower surface (back surface) of the n-type semiconductor layer, or the substrate. If it is present, it is possible to prevent the end face protective film material from flowing around and depositing on the lower surface (back surface) of the substrate. As a result, for example, an insulating end face protective film material is formed on the electrodes formed on the upper and lower surfaces of the p-type semiconductor layer and the n-type semiconductor layer, resulting in a bonding failure. Can be difficult. Further, even when an insulating substrate is used, problems such as poor adhesion can be made difficult to occur when placed on a support or the like.
[0084]
【Example】
Hereinafter, a semiconductor laser device using a nitride semiconductor will be described as an example. In the present invention, as a device structure of an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer constituting the nitride semiconductor layer. Is not particularly limited, and various layer structures can be used. Examples of the device structure include a laser device structure described in Examples described later, but other laser structures can also be applied. Specific examples of nitride semiconductors include nitride semiconductors such as GaN, AlN, or InN, III-V group nitride semiconductors that are mixed crystals thereof, and further include B, P, and the like. A thing etc. can be used. Nitride semiconductor growth is known to grow nitride semiconductors such as MOVPE, MOCVD (metal organic chemical vapor deposition), HVPE (halide vapor deposition), MBE (molecular beam vapor deposition). All methods are applicable.
[0085]
[Example 1]
(substrate)
As the substrate, a sapphire substrate having a C-plane as a main surface is used. The substrate is not particularly limited to this, and various substrates such as a sapphire substrate, an SiC substrate, an Si substrate, a spinel substrate, and a GaN substrate having the R surface and the A surface as main surfaces can be used as necessary. .
[0086]
(Underlayer)
An undoped GaN layer is grown at 2.5 μm at a temperature of 1050 ° C. ₂ A protective film made of 0.27 μm is formed. This SiO ₂ The protective film forms a stripe-shaped opening (non-mask region) by etching. This protective film is formed so that the stripe width is 1.8 μm and the direction is substantially perpendicular to the orientation flat surface, and the ratio of the protective film to the opening is set to 6:14. Next, an undoped GaN layer is grown to a thickness of 15 μm. At this time, the GaN layer grown on the opening is made of SiO. ₂ It grows laterally on the top and finally SiO ₂ Grown so that GaN is aligned in the upward direction.
[0087]
(Buffer layer)
Next, the temperature is set to 500 ° C. and trimethylgallium (TMG), ammonia (NH ₃ Si-doped Al _0.02 Ga _0.98 A buffer layer made of N is grown to a thickness of 1 μm.
[0088]
(N-type contact layer)
Subsequently, at 1050 ° C., similarly, TMG, ammonia gas, and silane gas as the impurity gas, Si-doped n-Al _0.02 Ga _0.98 An n-type contact layer made of N is grown to a thickness of 3.5 μm. The film thickness of this n-type contact layer should just be 2-30 micrometers.
[0089]
(Crack prevention layer)
Next, using TMG, TMI (trimethylindium), ammonia, the temperature is set to 800 ° C., and Si-doped n-In _0.05 Ga _0.95 A crack prevention layer made of N is grown to a thickness of 0.15 μm. This crack prevention layer can be omitted.
[0090]
(N-type cladding layer)
Next, the temperature is set to 1050 ° C., TMA (trimethylaluminum), TMG, and ammonia are used as source gases, and undoped Al _0.05 Ga _0.095 An A layer made of N and a B layer made of GaN doped with Si are grown to a thickness of 50 mm. Then, this operation is repeated 110 times, and the A layer and the B layer are alternately stacked to grow an n-type cladding layer made of a multilayer film (superlattice structure) having a total film thickness of 1.1 μm. At this time, if the mixed crystal ratio of Al in the undoped AlGaN is in the range of 0.02 or more and 0.3 or less, a refractive index difference that sufficiently functions as a cladding layer can be provided.
[0091]
(N-type light guide layer)
Next, TMG and ammonia are used as source gases at the same temperature, and an n-type light guide layer made of undoped GaN is grown to a thickness of 0.15 μm. This layer may be doped with n-type impurities.
[0092]
(Active layer)
Next, the temperature is set to 800 ° C., TMI (trimethylindium), TMG, and ammonia are used as raw materials, silane gas is used as an impurity gas, and Si-doped In _0.02 Ga _0.98 A barrier layer made of N is grown to a thickness of 140 mm. Subsequently, silane gas was turned off and undoped In _0.1 Ga _0.9 A well layer made of N is grown to a thickness of 70 mm. This operation is repeated twice, and finally Si-doped In _0.02 Ga _0.98 A barrier layer made of N is grown to a thickness of 140 Å to grow an active layer of a multiple quantum well structure (MQW) having a total thickness of 560 Å.
[0093]
(P-type electron confinement layer)
N at the same temperature ₂ In the atmosphere, Mg-doped Al _0.25 Ga _0.75 A p-type electron confinement layer made of N is grown to a thickness of 30 mm. Then H ₂ In the atmosphere, Mg-doped Al _0.25 Ga _0.75 A p-type electron confinement layer made of N is grown to a thickness of 70 mm.
[0094]
(P-type light guide layer)
Next, the temperature is set to 1050 ° C., TMG and ammonia are used as source gases, and a p-type light guide layer made of undoped GaN is grown to a thickness of 0.15 μm. The p-type light guide layer is grown as undoped, but may be doped with Mg.
[0095]
(P-type cladding layer)
Next, undoped Al _0.08 Ga _0.92 An A layer made of N is grown to a thickness of 80 、, and a B layer made of Mg-doped GaN is grown thereon to a thickness of 80 Å. This is repeated 28 times, and the A layer and the B layer are alternately laminated to grow a p-type cladding layer made of a multilayer film (superlattice structure) having a total film thickness of 0.45 μm. When a p-type cladding layer is made of a superlattice in which at least one nitride semiconductor layer containing Al is included and nitride semiconductor layers having different bandgap energies are stacked, impurities are both highly doped in one layer. Although so-called modulation doping tends to improve the crystallinity, both may be doped in the same manner.
[0096]
(P-type contact layer)
Finally, a p-type contact layer made of Mg-doped GaN is grown on the p-type cladding layer at 1050 ° C. to a thickness of 150 mm. The p-type contact layer is p-type In _x Al _y Ga _1-xy N (x.ltoreq.0, y.ltoreq.0, x + y.ltoreq.1), preferably Mg-doped GaN provides the most preferable ohmic contact with the p-electrode. After the completion of the reaction, the wafer is annealed at 700 ° C. in a nitrogen atmosphere in the reaction vessel to further reduce the resistance of the p-type layer.
[0097]
(N-type layer exposure)
After the nitride semiconductor is grown as described above to form a laminated structure, the wafer is taken out of the reaction vessel, and SiO 2 is deposited on the surface of the uppermost p-type contact layer. ₂ After forming a protective film made of RIE (reactive ion etching), Cl is used. ₂ Etching with a gas exposes the surface of the n-type contact layer that forms the n-electrode. At this time, the resonator surface may be formed by etching. Although it is preferable to carry out simultaneously with the exposure of the n-type contact layer, it can also be carried out in a separate process.
[0098]
(Ridge formation)
Next, in order to form a stripe-shaped waveguide region, a Si oxide (mainly SiO 2) is formed on almost the entire surface of the uppermost p-type contact layer by a CVD apparatus. ₂ ) Is formed to a thickness of 0.5 μm, a mask having a predetermined shape is formed on the protective film by a photolithography technique, and CHF is formed by an RIE apparatus. ₃ A protective film made of striped Si oxide is formed by etching using a gas. Using this Si oxide protective film as a mask, SiCl ₄ The semiconductor layer is etched using gas to form a ridge stripe above the active layer. At this time, the width of the ridge is set to 1.6 μm.
[0099]
(First insulating film)
SiO ₂ With the mask formed, ZrO is formed on the surface of the p-type semiconductor layer. ₂ A first insulating film is formed with a film thickness of about 550 mm. The first insulating film may be provided on the entire surface of the semiconductor layer by masking the n-side ohmic electrode formation surface. In addition, a portion where the insulating film is not formed can be provided so as to be easily divided later.
[0100]
After forming the first insulating film, the wafer is heat-treated at 600 ° C. Thus, SiO ₂ In the case of forming a material other than the first insulating film, after forming the first insulating film, heat treatment is performed at 300 ° C. or higher, preferably 400 ° C. or higher and below the decomposition temperature of the nitride semiconductor (1200 ° C.). You can stabilize the membrane material. In particular, in the process after the formation of the first insulating film, mainly SiO. ₂ When device processing is performed using as a mask, the SiO ₂ It can be made difficult to dissolve in a mask dissolving material used when the mask is removed later. The heat treatment step of the first insulating film can be omitted depending on the material and process of the first insulating film, and the order of the steps can be selected as appropriate, for example, it is performed simultaneously with the heat treatment of the ohmic electrode. Can do. After heat treatment, it is immersed in a buffered solution to form SiO formed on the upper surface of the ridge stripe ₂ Is dissolved and removed by a lift-off method. ₂ ZrO on the p-type contact layer (and on the n-type contact layer) ₂ Remove. As a result, the upper surface of the ridge is exposed and the side surface of the ridge is exposed to ZrO. ₂ It becomes a structure covered with.
[0101]
(Ohmic electrode)
Next, a p-side ohmic electrode is formed by sputtering on the ridge outermost surface on the p-type contact layer and on the first insulating film. For this p-side ohmic electrode, Ni / Au (100Å / 1500Å) is used. An n-side ohmic electrode is also formed on the upper surface of the n-type contact layer. The n-side ohmic electrode is made of Ti / Al (200Å / 5500Å), and is formed in a stripe shape parallel to the ridge and having the same length. After these electrodes are formed, heat treatment is performed at 600 ° C. in a mixed atmosphere of oxygen and nitrogen.
[0102]
(Second insulating film)
Next, a resist covering the entire surface of the p-side ohmic electrode on the ridge and a part of the upper portion of the n-side ohmic electrode is formed. Next, SiO ₂ A second insulating film made of is formed on substantially the entire surface and lifted off, thereby forming a second protective film in which the entire upper surface of the p-side ohmic electrode and a part of the n-side ohmic electrode are exposed. The second insulating film and the p-side ohmic electrode may be formed so as to be separated from each other, or may be formed so as to partially overlap each other. In consideration of the subsequent division, the first and second insulating films and electrodes may not be formed in a stripe-shaped range having a width of about 10 μm across the division position.
[0103]
The second insulating film is provided so as to cover the entire surface except the upper part of the p-side and n-side ohmic electrodes. A preferable material is an oxide containing at least one element selected from the group consisting of Si, Ti, V, Zr, Nb, Hf, and Ta, and formed of at least one of SiN, BN, SiC, AlN, and AlGaN. Among them, SiO 2 is particularly preferable as SiO 2 ₂ , Al ₂ O ₃ , ZrO ₂ TiO ₂ And a single layer film or a multilayer film.
[0104]
(Pad electrode)
Next, a pad electrode is formed so as to cover the ohmic electrode. At this time, it is preferable to form the second insulating film so as to cover it. The p-side pad electrode is laminated in the order of Pt / Ti / Pt / Au (1000 Å / 50 Å / 1000 Å / 6000 Å). Further, the n-side pad electrode is formed of Ni / Ti / Au (1000/1000/8000) from below. These pad electrodes are in contact with the p-side ohmic electrode and the n-side ohmic electrode in a stripe shape through the second insulating film, respectively.
[0105]
(Cleavage and resonator surface formation)
Next, the substrate is polished and adjusted so as to have a film thickness of about 150 μm, and then a scribe groove is formed on the back surface of the substrate. The cleavage plane of the nitride semiconductor layer is the M plane (11-00 plane) of the nitride semiconductor, and this plane is the resonator plane.
[0106]
(End face protection film formation)
On the resonator surface formed as described above, an end face protective film is provided on both the emission-side and monitor-side resonator surfaces. The material is SiO ₂ And ZrO ₂ These are laminated to form a dielectric multilayer film. The surface of the resonator on the light reflection side (monitor side) is made of ZrO using a sputtering device such as an ECR sputtering device. ₂ A protective film consisting of ₂ And ZrO ₂ Are alternately stacked to form a highly reflective film. Here, the protective film and the SiO constituting the highly reflective film ₂ Membrane and ZrO ₂ The thickness of the film can be set to a preferable thickness according to the emission wavelength from the active layer. In addition, it is not necessary to provide anything on the resonator surface on the light emitting side, and ZrO may be used by using a sputtering apparatus. ₂ , Nb ₂ O ₅ , Al ₂ O ₃ , ZrO ₂ A first low reflection film comprising SiO2 and ₂ A second low reflection film may be formed. Moreover, it can also be set as a multilayer film (For example, it is set as 6.5 pairs using the said material).
[0107]
At the time of film formation, as shown in FIG. 6, a spacer having a stripe-shaped protrusion is placed so as to sandwich each bar-shaped laser. At this time, the protruding portion is arranged so as to be positioned at the upper part on the substrate side. The length of the protrusion is about 75 μm from the plane. In this state, a protective film of the above material is laminated using an ECR sputtering apparatus. The end face protective film thus formed is a p-type semiconductor layer, an active layer, an n-type active layer, and an end face protective film having a uniform film thickness up to a part of the substrate. In the film thickness gradient region in the vicinity of the uniform region, the region having the maximum transmittance difference is provided. In addition, a plurality of transmittance difference regions are provided in the substrate rear surface direction. The end face protective film is hardly formed on the end face of the substrate near the back surface of the substrate, and the substrate is exposed. Almost no end face protective film is deposited on the back surface of the substrate.
[0108]
Finally, a groove is formed by scribing so as to be substantially parallel to the ridge stripe, and a bar is cut at the groove portion to obtain the semiconductor laser device of the present invention. As the scribing method, mechanical or physical scribing using a blade such as a cutter, optical or thermal scribing using a YAG laser, or the like can be used. The scribing direction may be from the semiconductor layer side or from the substrate side, and various optimum methods can be selected depending on the shape of the element, the type of the substrate, and the like. The nitride semiconductor laser device obtained as described above has a threshold current density of 2.5 kA / cm at room temperature. ² , Capable of continuous oscillation at an oscillation wavelength of 405 nm at a high output of 60 mW. Light that can be detected by the detector is output from the monitor side and can be driven with good control, and has a good FFP with less noise (unevenness).
[0109]
【The invention's effect】
Although the semiconductor element of the present invention is a continuous end face protective film, the end face protective film has a film thickness inclined region in which the film thickness decreases in a specific area thereof, so that it has a high reflectivity so that light can be emitted. Even if it is a resonator surface on the monitor side where extraction efficiency is possible, it can be a multi-functional end face protective film that can output light that can be detected by the detector from the end face other than the waveguide region. Also, on the emission side, by reducing the transmittance by the thickness gradient region, it is possible to prevent light from being emitted from outside the waveguide region while maintaining high transmittance with high extraction efficiency. A possible multi-functional end face protective film can be obtained. Thus, by utilizing the fact that the gradient rate of the film thickness of the continuous film does not match the gradient rate of the transmittance, a semiconductor laser element having excellent characteristics can be obtained. In addition, by using a specific spacer, the formation region of the film thickness gradient region can be formed with good controllability, so that a multifunction protective film can be easily formed without requiring a separate step such as a mask formation step. Can do. In addition, since the end face protective film can be prevented from entering the upper and lower surfaces of the device, it is possible to obtain a highly reliable semiconductor laser device without deteriorating electrical continuity and adhesion during use. .
[Brief description of the drawings]
FIG. 1A is a schematic perspective view illustrating a semiconductor laser device of the present invention.
(B) AA sectional view of FIG.
(C) BB sectional view of FIG.
FIG. 2 is a partial schematic cross-sectional view illustrating a semiconductor laser device of the present invention.
FIG. 3 is a partial schematic cross-sectional view illustrating a semiconductor laser device of the present invention.
FIG. 4 is a partial schematic cross-sectional view illustrating a semiconductor laser device of the present invention.
FIG. 5 is a partial schematic cross-sectional view illustrating a semiconductor laser device of the present invention.
6A is a schematic perspective view illustrating a method for manufacturing a semiconductor laser device of the present invention. FIG.
(B) Partial enlarged sectional view of FIG.
(C) Partially enlarged top view of FIG.
7A is a schematic perspective view illustrating a method for manufacturing a semiconductor laser device of the present invention. FIG.
(B) Sectional view for explaining the film formation state of FIG.
(C) Sectional view for explaining the film formation state of FIG.
FIG. 8A is a schematic perspective view illustrating a method for manufacturing a semiconductor laser device of the present invention.
(B) Sectional view for explaining the film formation state of FIG.
(C) Sectional view for explaining the film formation state of FIG.
FIG. 9A is a schematic cross-sectional view illustrating a semiconductor laser device of the present invention.
(B) Schematic cross-sectional view illustrating the semiconductor laser device of the present invention
[Brief description of symbols]
101, 201, 301, 401, 501, 601, 701, 901 ... substrate
102, 202, 302, 402, 502, 602, 702, 802, 902... N-type nitride semiconductor layer
103, 203, 303, 403, 503, 603, 703, 803, 903... P-type nitride semiconductor layer
104, 204, 304, 404, 504, 604, 704, 804, 904... Active layer
105, 205, 305 ... p-side ohmic electrode
106, 206, 306... P-side pad electrode
107 ... n-side ohmic electrode
108 ... n-side pad electrode
109: First insulating film
110 ... second insulating film
111, 211, 311, 411, 511, 611 ... end face protective film
711 (a), 811 (a) ... end face protective film (film thickness non-inclined region)
711 (b), 811 (b) ... end face protective film (film thickness gradient region)
612, 712, 812, 912 ... spacer
612 (a), 712 (a), 812 (a) ... protrusion of the spacer
612 (b): spacer recess
913 ... Stepped portion

Claims (14)

A nitride semiconductor layer including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer is provided, and the nitride semiconductor layer includes a striped waveguide region and a resonator surface at an end of the waveguide region. A semiconductor laser device having an end face,
On the end face, having an end face protective film continuous from the resonator face to the non-resonator face,
The end face protective film has a film thickness non-inclined region and a film thickness inclined region in which the film thickness decreases on the non-resonator surface,
In the film thickness gradient area, the film thickness non-gradient area and the film thickness gradient area have a maximum transmittance difference area,
The thickness gradient region is provided on the monitor side end surface,
2. The semiconductor laser device according to claim 1, wherein the end face protective film on the monitor side has a higher transmittance in the film thickness gradient region than in the film thickness non-tilt region on the resonator surface. A nitride semiconductor layer including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer is provided, and the nitride semiconductor layer includes a striped waveguide region and a resonator surface at an end of the waveguide region. A semiconductor laser device having an end face,
On the end face, having an end face protective film continuous from the resonator face to the non-resonator face,
End surface protective film has a film thickness non-inclined areas, and a film thickness gradient region thickness on non-resonant surface is reduced,
In the film thickness gradient area, the film thickness non-gradient area and the film thickness gradient area have a maximum transmittance difference area,
The end face has a stepped portion protruding from the resonator surface, and the film thickness inclined region is provided between the stepped portion and the resonator surface. A nitride semiconductor layer including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer is provided, and the nitride semiconductor layer includes a striped waveguide region and a resonator surface at an end of the waveguide region. A semiconductor laser device having an end face,
On the end face, having an end face protective film continuous from the resonator face to the non-resonator face,
End surface protective film has a film thickness non-inclined areas, and a film thickness gradient region thickness on non-resonant surface is reduced,
In the film thickness gradient area, the film thickness non-gradient area and the film thickness gradient area have a maximum transmittance difference area,
The film thickness gradient area is provided on both end faces of the monitor side end face and the emission side end face,
The end face protective film on the monitor side has a higher transmittance in the thickness gradient region than the transmittance in the non-gradient region on the resonator surface,
The semiconductor laser device according to claim 1, wherein the emission-side end face protective film has a lower transmittance in the film thickness gradient region than in the film thickness non-tilt region on the resonator surface.   4. The semiconductor laser device according to claim 1, wherein the film thickness inclined region is provided so as to be inclined in a direction substantially parallel to a stacked surface of the semiconductor layers. 5.   5. The semiconductor laser device according to claim 1, wherein the film thickness inclined region is provided so as to be inclined with the waveguide region as a center. 6.   6. The film thickness gradient region includes a plurality of regions having a transmittance difference, and has a maximum region of the transmittance difference near a boundary between the film thickness gradient region and the film thickness non-tilt region. The semiconductor laser device according to claim 1.   3. The semiconductor laser device according to claim 2, wherein the end face protective film has a higher transmittance in a film thickness inclined region than in a film thickness non-inclined region on the resonator surface.   3. The semiconductor laser device according to claim 2, wherein the end face protective film has a lower transmittance in the thickness gradient region than in the thickness non-tilt region on the resonator surface.   9. The semiconductor laser device according to claim 1, wherein the thickness gradient region is provided on an end surface on an n-type semiconductor layer side.   10. The semiconductor laser device according to claim 1, wherein the film thickness gradient region is provided on an end surface of a substrate provided on the n-type semiconductor layer side. 11.   The semiconductor laser device according to claim 10, wherein the substrate is a GaN substrate.   12. The semiconductor laser device according to claim 2, wherein the stepped portion is formed of an n-type semiconductor layer protruding from the resonator surface.   The semiconductor laser device according to claim 2, wherein an end face protective film is provided at the stepped portion. A method of forming an end face protective film on an end face including an exposed resonator surface of a bar-shaped laser element comprising a nitride semiconductor layer comprising an n-type semiconductor layer, an active layer, and a p-type semiconductor layer,
When forming the end face protective film in a state where the laser element is sandwiched using a spacer having a protrusion, the protrusion is separated from the end face and extends to a part of the end face. By forming the end face protective film on the end face protective film, the film thickness non-inclined region on the end face protective film, the film thickness inclined region in which the film thickness decreases on the non-resonator surface, and the film thickness inclined region A method of manufacturing a semiconductor laser device, comprising forming a maximum transmittance difference region between the non-gradient film thickness region and the gradient film thickness region .

Images