JPH05235473A - Surface light emitting device and fabrication thereof - Google Patents

Abstract

PURPOSE:To reduce damage on an active layer by employing a semiconductor multilayered film mirror for an upper mirror provided on the upper part of a cavity region including the active layer, and forming portions from a lower mirror to the cavity region and the upper mirror with one time epitaxial growth. CONSTITUTION:A lower mirror 3 comprising an n-type semiconductor multilayered film is formed on an n-type semiconductor (GaAs) substrate 1 as a substrate side mirror. Successively, there are grown a cavity region 2 which includes at the center thereof an InGaAs distorted quatum well layer as an active layer and comprises AlGaAs including a light emitting layer therein and an upper mirror 12 comprising a semiconductor multilayered film. The growth is done by only one crystal growth in order to easily satisfy optical conditions. For easily and completely ensuring matching between the cavity 2 and the upper mirror 12, a semiconductor multilayered film mirror is employed for the upper mirror 12 and since the mirror 20 ion-implanted after mesa etching, damage on the active layer is suppressed to the minimum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface emitting diode or a surface emitting semiconductor laser which emits light or oscillates in a direction perpendicular to a substrate and a method for manufacturing the same, and more particularly to reduction of element resistance and low threshold voltage. The present invention provides a highly efficient planar light emitting device and a method for manufacturing the same.

[0002]

2. Description of the Related Art A surface emitting diode or a surface emitting semiconductor laser of a spontaneous emission control type which emits light or oscillates in a direction perpendicular to a substrate is a two-dimensional device which is fine and has high directivity and high efficiency (or a small threshold value). Suitable for arraying,
It is expected to open a new path for optical applications. However, in order to efficiently control spontaneous emission and obtain laser oscillation at a low threshold value, a mirror having a reflectance close to 100% is required. Therefore, a DBR mirror (Distributed Bragg Reflector) made of a semiconductor or dielectric multilayer film
Is used.

FIG. 4 shows an example of a conventional planar light emitting device structure, in which a cavity region 2 including a light emitting layer of a GaAs or InGaAs strained layer is provided on an n-type semiconductor (n-GaAs) substrate 1 and its cavity thickness is set. The so-called microcavity type element has a length of 1 or 1/2 optical wavelength.
A lower mirror 3 made of an n-type semiconductor multi-layer film and an upper mirror 4 made of a p-type semiconductor multi-layer film are formed on both sides of the cavity region 2 including the light emitting layer.
A semiconductor multilayer mirror having a thickness of λ / 4n (λ is an emission wavelength and n is a refractive index) of lAs or AlGaAs / AlAs is used. This element is called a funnel shape, and is provided with a semi-insulating region 5 inside by implanting protons or oxygen ions to achieve current confinement and low resistance. That is, in the implantation of protons or oxygen ions, by appropriately selecting the implantation voltage and the implantation amount, it is possible to insulate only the inside while maintaining the original electrical conductivity on the surface. Alternatively, it is possible to insulate only the inside by implanting p-type ions such as beryllium into the surface after implanting protons or oxygen ions. When the p-type electrode 7 is formed in this donut-shaped ion-implanted portion and the n-type electrode 6 is further formed on the substrate side, current flows from the donut-shaped electrode while avoiding the internal semi-insulating region 5 due to proton or oxygen ion implantation, Light is emitted only in a predetermined light emitting region 8 in the active layer. In this structure, by making the ohmic contact part a donut-shaped part around the light emitting region 8, the area thereof can be increased and the resistance can be made low. Further, since no electrode is provided directly on the light emitting portion, there is an advantage that a top emission type element can be easily manufactured. However, this conventional device has the following drawbacks. That is, since proton or oxygen ion implantation is performed from the surface of the upper semiconductor mirror to the active layer thereunder, it is necessary to increase the implantation voltage to allow ions to reach deep. Increasing the injection voltage increases damage to the active layer. The damage to the active layer increases the non-radiative centers around the effective light emitting region 8, which kills the carriers injected into the light emitting region 8, thus lowering the light emitting efficiency. As a result, the light emission output of the light emitting diode is lowered and the threshold value of laser oscillation is increased. Further, since protons or oxygen ions are implanted deep inside, lateral spread thereof becomes a problem, and it becomes difficult to finely limit the light emitting region 8. Further, since there is no optical guide structure in the upper part of the cavity, there is a problem that the guide loss is large, which raises the laser threshold value.

FIG. 5 shows another example of a conventional element structure. The current confinement structure of this device is similar to the funnel type in which the semi-insulating region 5 is formed in the same way as the above-mentioned device, and the part 10 of the clad layer on the upper side of the cavity is p-shaped.
The mold is formed, and current is injected through the mold. As the upper mirror, the upper mirror 11 made of a dielectric multilayer film is used without using the semiconductor DBR mirror. Unlike the above-mentioned element, this element requires less ion implantation voltage, so there is little damage and the emission region can be miniaturized, and the threshold value is lowered because the optical guide is formed on the upper part. Conceivable. However, there is a problem that good device characteristics cannot be actually obtained. This is because etching of the dielectric multilayer film is more difficult than that of the semiconductor multilayer film, and it is difficult to form a fine structure, and when the upper mirror 11 made of the dielectric multilayer film is formed on the cavity region 2 including the light emitting layer. In addition, it is considered that optical foreign substances, that is, oxides and dirt of semiconductor crystals are easily mixed into the interface 9 and the condition of the microcavity is easily deteriorated. In the microcavity surface emitting device, the peak position of the light intensity distribution of the standing wave generated in the resonator is accurately aligned with the center of the cavity, and the active layer is placed at that position. The luminous output is significantly reduced.
Since the optical nonuniformity in the very vicinity of the cavity has a great influence on the microcavity characteristics, the upper mirror 11 made of a dielectric multilayer film different from the semiconductor is provided in the very vicinity of the cavity region 2 including the light emitting layer. As a result, the device characteristics were deteriorated.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks of the prior art, to provide a surface emitting element and a surface emitting element having a fine light emitting region, a low laser oscillation threshold value and a low resistance. Type semiconductor laser and its manufacturing method.

[0006]

In order to achieve the above object of the present invention, a semiconductor multilayer film is formed on the upper mirror in order to easily and completely match the cavity region including the light emitting layer with the upper mirror. Using a mirror, the lower mirror, the cavity region and the upper mirror are successively formed by one epitaxial growth. Further, in order to minimize the damage to the active layer by reducing the voltage of ion implantation and to easily form the light emitting region and the optical guide structure of the fine structure, the semiconductor multilayer film mirror is mesa-etched to make the active layer. Shorten the distance to. The ion implantation and the electrode formation are performed in a self-aligned manner by using the mesa portion as a mask for ion implantation.

According to the present invention, a first semiconductor mirror made of a semiconductor multilayer film, a cavity region containing an active layer, and a second semiconductor film made of a semiconductor multilayer film different from the first semiconductor mirror are formed on a semiconductor substrate. At least with a mirror,
A surface-type light-emitting device that emits light or oscillates in a direction perpendicular to a substrate, wherein the second semiconductor mirror has a shape having a convex portion, and the second semiconductor mirror has a layer around the convex portion. This is a planar light emitting device having a structure in which a semi-insulating region is set in the vicinity of the active layer in the thickness direction and an electrode for current injection is provided in the peripheral portion of the convex portion of the second semiconductor mirror.

According to the present invention, a first semiconductor mirror portion formed of at least a semiconductor multilayer film, a cavity region including an active layer, and a semiconductor multilayer film different from the first semiconductor mirror are formed on a semiconductor substrate. Step of sequentially stacking the second semiconductor mirror portion, forming a mask for mesa etching the surface of the second semiconductor mirror portion, and forming a convex portion on the second semiconductor mirror portion by mesa etching. Surface emitting including at least a step, a step of performing ion implantation using the mesa etching mask formed on the convex portion as a mask for ion implantation, and a step of depositing an electrode layer and performing lift-off to form an upper electrode It is a method of manufacturing an element. In addition, the above second mesa etching
After the step of forming the convex portion on the semiconductor mirror portion, the step of removing the mask provided for mesa etching, the step of implanting ions using the second semiconductor mirror portion having the convex portion as a mask, and the electrode lift-off And a step of forming an upper electrode by vapor-depositing an electrode layer and performing lift-off to form an upper electrode. Further, at least the step of forming an upper electrode by performing ion implantation using the second semiconductor mirror portion having the convex portion as a mask and then depositing an electrode layer on the entire surface of the second semiconductor mirror having the convex portion. It is a method of manufacturing a surface emitting device including the same.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of the structure of a surface emitting element and a surface emitting semiconductor laser according to the present invention.
It is a schematic diagram which shows the typical manufacturing process of the surface emitting element of this invention at (5). First, a lower mirror 3 made of an n-type semiconductor multilayer film is formed as a substrate-side mirror on an n-type semiconductor (GaAs) substrate 1. For example, the composition is AlAs and Ga
As, the quarter optical wavelength is 80.
3 nm and 66.9 nm. Where emission wavelength (λ)
Was 980 nm, and the refractive indices (n) of AlAs and GaAs were 3.05 and 3.66, respectively. When this material is used to form 20.5 pairs (the uppermost layer is AlAs), the thickness of the entire layer is 3.0 μm, and the maximum value of the reflectance from the light emitting layer side to the substrate side is 99.8%. .. The Al composition and the thickness of AlAs and GaAs can be changed depending on the desired reflectance, resistance value, emission wavelength and the like. Next, an InGaAs strained quantum well layer is formed as an active layer in the center, and a cavity region (so-called λ cavity) 2 including a light emitting layer is formed inside Al _0.3 Ga _0.7 As having a thickness of λ / n, and an upper portion formed of a semiconductor multilayer film. Grow the mirror 12. These growths are formed by a single crystal growth in order to easily satisfy various optical conditions. The upper mirror 12 made of a semiconductor multilayer film,
As with the lower mirror 3 made of an n-type semiconductor multilayer film, Al
Although it is composed of a multilayer film having a quarter optical wavelength thickness of As and GaAs or a semiconductor composition corresponding to these, if the cavity length is λ, the lowermost layer 13 of the upper mirror composed of a p-type semiconductor multilayer film should be AlAs. For example, from the magnitude of the refractive index, the center of the cavity can be set to the maximum intensity of the oscillation mode (antinode of standing wave). Also, in the case of a λ / 2 cavity or the like, the refractive index configuration of the mirror is adjusted so as to satisfy the same condition. The electric conductivity type of the upper mirror 12 made of a semiconductor multilayer film is all p-type in the present embodiment, but only one pair or a few pairs near the cavity through which holes flow may be p-type, and the other portions. May be an n-type or a non-doped type that has low optical absorption. Next, a resist (or polyimide) 15 serving as a mask for mesa etching is formed on the surface of the upper mirror 12 made of a semiconductor multilayer film [FIG. 2 (1)]. After that, a part of the upper mirror 12 made of the semiconductor multilayer film is dry or wet etched in a mesa shape to the vicinity of the cavity [FIG. 2 (2)]. The mesa-etched surface is preferably made of GaAs, which facilitates ohmic contact. When it is desired to increase the thickness of the p-type current injection layer (the ohmic layer made of GaAs in this embodiment) 14 to reduce the series resistance, the quarter-wave optics should be maintained so as not to impair the standing wave condition of the microcavity. It shall be an odd multiple of the thickness. Further, in order to improve the uniformity of the current in the active layer, the lowermost layer of the p-type current injection layer 14 may be a few pairs of p-type semiconductor auxiliary mirrors 13. Next, as it is, that is, using the resist for mesa etching and the mesa type semiconductor layer as a mask, proton or oxygen ion implantation is performed. If necessary, a semi-insulating region 5 as an internal insulating layer and a surface p layer are formed by beryllium ion implantation or the like [FIG.
(A) of (3)], and finally the p-type electrode 7 is formed [FIG.
(4) (a)], electrode patterning is performed by lift-off in a self-aligned manner ((a) of FIG. 2 (5)). As described above, in this embodiment, a semiconductor multilayer film mirror is used for the upper mirror in order to easily and completely match the cavity with the upper mirror, and ion implantation is performed after mesa etching of the semiconductor multilayer film mirror. Therefore, the damage to the active layer can be suppressed to a minimum without increasing the voltage for ion implantation, and the fine light emitting layer and the fine optical guide can be easily formed. Further, since the p-type semiconductor multilayer film is not used, the surface-type light-emitting device or the surface-type light-emitting type which has low resistance, low optical loss, high efficiency and low threshold light emission from the top surface and the bottom surface. A semiconductor laser is obtained. In the method for manufacturing the surface light emitting device of the present invention, as shown in FIG.
After the step (2), the resist 15 is removed, and ion implantation is performed using the mesa-etched mesa portion 18 as a mask [FIG. 2 (3) (b)]. The ion implantation portion 16 in the mesa portion 18 electrically serves as an insulating layer, but no current flows in the device operation, and the ion implantation does not impair the performance as a DBR mirror.
Even if is used as the upper surface DBR mirror, the current confinement region (light emitting region) is formed by the mesa portion 18 in a self-aligned manner, so that a cavity without mirror loss is effectively formed. Next, the electrode lift-off lithograph [Fig. 2
(4) (b)] is formed, and the electrode is patterned by vapor deposition and lift-off of the electrode [(b) of FIG. 2 (5)].
By performing the process described above, it is possible to obtain a high performance planar light emitting device having a fine light emitting region, a low threshold value such as laser oscillation, a low resistance and the like. In the method for manufacturing a surface light emitting device of the present invention, after the step shown in (b) of FIG. 2 (3), an electrode layer is vapor-deposited on the entire surface [(c) of FIG. 2 (5)]. Thus, a back-emission type device can be obtained. In this case, by providing a matching layer on the uppermost layer of the upper semiconductor mirror and using a high-reflectance metal such as gold for the electrode, a high-reflectance mirror that is a composite mirror of the semiconductor DBR and the metal mirror can be obtained.

Next, in the present embodiment, the effect of using a semiconductor multi-layer film mirror as the upper mirror and growing the lower mirror and the cavity consistently by epitaxial growth will be described. For example, in the conventional element structure (FIG. 5), some optical nonuniformity or foreign matter is mixed between the cavity region 2 including the light emitting layer and the upper mirror 11 formed of the dielectric multilayer film. This tends to occur even after taking out from the crystal growth furnace or when forming the dielectric multilayer mirror. 3 (1) and 3 (2) show reflectance spectra showing how the cavity characteristics of the semiconductor laser are affected by the presence of the optical nonuniformity and the inclusion of foreign matter. It should be noted that FIG.
It is the graph which expanded (lambda) of (1) the range of 970-990 nm. Al on the n-GaAs substrate as a lower mirror
11.5 pairs of As / GaAs, cavity length 1 wavelength (λ
This is a case where four pairs of SiO ₂ / TiO ₂ are formed as a cavity and an upper mirror. Here, the refractive index difference (Δn) of each DBR mirror is Δn / n = 0.1 in the case of a semiconductor mirror.
82, in the case of a dielectric mirror, Δn / n = 0.369. In the figure, the curve (a) is an ideal reflectance spectrum when there is no optical nonuniformity or foreign matter,
The curve (b) shows the case where an absorptive thin film (for example, a thickness of 1 nm and a complex refractive index of 2.6 to 5.3i) is mixed in the cavity / dielectric mirror interface 24 as an optical nonuniformity or as a foreign substance. In (a) above, the reflectance at the cavity mode wavelength is 0% (transmittance 100%) and the cavity mode width is also very sharp, but in (b), the cavity mode wavelength shift and the cavity mode reflectance are Is increased (the transmittance is decreased) and the cavity mode width is increased. This seriously affects the oscillation characteristics such as the threshold value of the surface emitting laser. (C) and (d) show the case where the same foreign matter and dielectric mirror are installed after inserting 1 pair (c) and 3 pairs (d) of semiconductor mirrors into the cavity. By inserting the semiconductor pair between the foreign matter and the cavity, the cavity characteristic approaches the ideal curve (a). In this way, by inserting a semiconductor pair into the cavity and increasing the number of semiconductor pairs, it is possible to reduce the effects of optical nonuniformity and contamination by foreign matter. If the number of semiconductor pairs is increased, the high reflectance as the upper mirror can be satisfied only by the semiconductor pairs, and the dielectric mirror on the semiconductor mirror becomes unnecessary. The thus configured structure is the upper mirror 12 made of a semiconductor multilayer film which is the upper mirror of this embodiment shown in FIG. As described above, the planar light emitting device of the present invention is
It is possible to obtain an element structure that does not impair the optical cavity characteristics, reduces damage due to ion implantation, and is effective even on a fine cavity surface. In the above embodiments, the case where the light emitting layer is an InGaAs strained quantum well and the multi-layer film mirror is an AlGaAs type is used, but the basic concept of the present invention is that the light emitting layer is GaAs or A
In the case of a quantum well of GaAs or a bulk thin film, further, an InGaAsP / InP long-wave light emitting device, an AlGaInP
It can also be applied to a visible light element or the like. In any case, the composition of the semiconductor mirror, the cavity composition, the ohmic composition, etc. can be appropriately optimized in consideration of the light emission characteristics, the electrical characteristics, etc. of the device. The quantum structure of the light emitting layer is not limited to the above-mentioned one-dimensional well structure, but also for two-dimensional and three-dimensional quantum wells, that is, quantum wires and quantum box types, the mirror characteristics should be set according to the emission spectrum width and the like. Thus, the structure of the present invention can be applied. Further, the element form can be applied not only to the surface emitting laser and the surface emitting diode, but also to the surface bistable laser, the surface amplifier / switch, the pnpn optical thyristor, and the optical logic element using them. is there.

[0011]

According to the surface-type light emitting device and the method of manufacturing the same of the present invention, a semiconductor multilayer mirror is used as the upper mirror provided above the cavity region including the active layer, and the lower mirror to the cavity region and the upper mirror are used. Is formed by one-time epitaxial growth, the matching between the cavity region and the upper mirror can be easily and completely achieved, and excellent optical cavity characteristics can be obtained. further,
Since the upper mirror made of a semiconductor multilayer film is mesa-etched to shorten the distance to the active layer, and the mesa-etched portions are used as the respective masks to form the semi-insulating regions or electrodes by ion implantation in a self-aligned manner. ,
Since the ion implantation voltage is small and the damage to the active layer can be made extremely small, a fine light emitting region and an optical guide structure can be easily formed, and a high performance surface emitting element, a surface semiconductor laser, etc. Can be realized.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a structure of a surface emitting element illustrated in an example of the present invention.

FIG. 2 is a schematic view showing a manufacturing process of the surface light-emitting device illustrated in the example of the present invention.

FIG. 3 is a graph showing the cavity characteristics (reflectance spectrum of a surface emitting laser structure) of the surface emitting element illustrated in the example of the present invention.

FIG. 4 is a schematic view showing an example of a structure of a conventional surface light emitting device.

FIG. 5 is a schematic view showing another example of the structure of a conventional surface light emitting device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... n-type semiconductor (n-GaAs) substrate 2 ... cavity region including a light emitting layer 3 ... lower mirror made of n-type semiconductor multilayer film 4 ... upper mirror made of p-type semiconductor multilayer film 5 ... semi-insulating region 6 ... n-type Electrode 7 ... P-type electrode 8 ... Emitting region 9 ... Interface 10 ... Clad layer part 11 ... Upper mirror made of dielectric multilayer film 12 ... Upper mirror made of semiconductor multilayer film 13 ... Upper mirror made of p-type semiconductor multilayer film Bottom layer of
Or p-type semiconductor auxiliary mirror 14 ... P-type current injection layer (ohmic layer made of GaAs) 15 ... Resist (or polyimide) 16 ... Ion injection part 17 ... Resist (or polyimide) 18 ... Mesa part (convex part)

Claims (4)

[Claims] 1. A first semiconductor mirror made of a semiconductor multilayer film on a semiconductor substrate, and a cavity region including an active layer,
A surface-type light-emitting device which includes at least a second semiconductor mirror made of a semiconductor multilayer film different from the first semiconductor mirror, and which emits light or oscillates in a direction perpendicular to the substrate, wherein the second semiconductor mirror is A semi-insulating region is formed in the peripheral portion of the convex portion of the second semiconductor mirror in the vicinity of the active layer in the layer thickness direction, and the peripheral portion of the convex portion of the second semiconductor mirror is formed. A surface-type light emitting device having a structure having an electrode for injecting a current in the interior. 2. A second semiconductor formed on a semiconductor substrate, at least a first semiconductor mirror portion formed of a semiconductor multilayer film, a cavity region including an active layer, and a semiconductor multilayer film different from the first semiconductor mirror. A step of sequentially laminating a mirror section, a step of forming a mask for mesa etching the surface of the second semiconductor mirror section, and a step of forming a convex section on the second semiconductor mirror section by mesa etching, A surface including at least a step of performing ion implantation using the mesa etching mask formed on the convex portion as a mask for ion implantation and a step of depositing an electrode layer and performing lift-off to form an upper electrode. Method of manufacturing a light emitting device. 3. The method according to claim 2, wherein after the step of forming the convex portion on the second semiconductor mirror portion by mesa etching, the step of removing the mask provided for the mesa etching and the second step of forming the convex portion. Surface emitting, which includes at least a step of implanting ions using the semiconductor mirror portion as a mask, a step of performing a lithographic process for electrode lift-off, and a step of depositing an electrode layer and performing lift-off to form an upper electrode. Manufacturing method of device. 4. The upper electrode according to claim 3, wherein after ion implantation using the second semiconductor mirror portion having the convex portion as a mask, an electrode layer is vapor-deposited on the entire surface of the second semiconductor mirror having the convex portion. A method for manufacturing a surface light-emitting device, comprising at least the step of forming.