JP4123554B2 - Manufacturing method of semiconductor laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser manufacturing method, and is particularly suitable for application to manufacturing a semiconductor laser having a so-called window structure.
[0002]
[Prior art]
AlGaInP-based semiconductor lasers have been applied in various fields since they have a shorter emission wavelength than AlGaAs-based semiconductor lasers. In recent years, this AlGaInP-based semiconductor laser has attracted attention as a laser light source for an optical disc device (DVD device) for recording / reproducing a digital video disc (DVD) capable of high-density recording.
[0003]
At present, AlGaInP semiconductor lasers for DVD devices are mainly those with an output of 5 mW for reproduction (reading), but in the future, those with a high output of 30 to 50 mW for recording (writing) will be required. ing.
[0004]
However, in the case of a conventional AlGaInP semiconductor laser, particularly in the wavelength band of 630 to 650 nm, if the output is increased, the end face breaks down, so that the output cannot be increased as expected. Therefore, it is important to prevent the end face deterioration by using a so-called window structure as the end face of the laser resonator.
[0005]
Conventionally, the most commonly used method for forming this window structure is to diffuse Zn from the upper surface of the substrate (wafer) before forming the end face by cleavage and into the area where the end face is formed by cleavage later. There is a method of locally increasing the band gap at the end face and reducing the optical loss in the vicinity of the end face by destroying the quantum well structure in FIG. 1 or by destroying the natural superlattice in the active layer.
[0006]
[Problems to be solved by the invention]
However, since the conventional window structure forming method as described above is difficult to control the Zn diffusion, Zn diffuses from about 100 μm from the end face of the laser resonator, thereby reducing the reliability of the element. there were. Moreover, in order to form the window structure, a Zn diffusion process is required in addition to a normal AlGaInP semiconductor laser manufacturing process, and thus the manufacturing process is complicated. Further, the conventional AlGaInP-based semiconductor laser has a current confinement structure in which the upper part of the p-type AlGaInP clad layer is patterned in a stripe shape, and an n-type GaAs current confinement layer is embedded on both sides thereof, so-called loss waveguide type Therefore, the drive current is large, and deterioration is likely to occur in portions other than the end faces.
[0007]
Accordingly, an object of the present invention is to provide a semiconductor laser manufacturing method capable of manufacturing a semiconductor laser having a window structure and an actual refractive index waveguide type by a simple process without degrading the reliability of the element. Is to provide.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a semiconductor laser manufacturing method according to the first aspect of the present invention comprises:
Growing a semiconductor layer forming a laser structure on the substrate, the first layer including a first conductivity type first clad layer, an active layer, and a second conductivity type second clad layer;
A groove is formed by etching the semiconductor layer around the region to be the stripe portion. At this time, the depth of the portion extending in the resonator length direction of the groove is a depth that does not reach the active layer. The depth of the portion extending in the direction perpendicular to the resonator length direction is to exceed the active layer,
And a step of growing and embedding a semiconductor layer having a band gap larger than that of the active layer inside the groove.
[0009]
A method for manufacturing a semiconductor laser according to a second aspect of the present invention comprises:
Growing a semiconductor layer forming a laser structure on the substrate, the first layer including a first conductivity type first clad layer, an active layer, and a second conductivity type second clad layer;
Forming a stripe-shaped first insulating film extending in a direction orthogonal to the resonator length direction and having a width corresponding to the resonator length on the semiconductor layer;
Etching the semiconductor layer to a depth that does not reach the active layer using the first insulating film as a mask;
Patterning the first insulating film to form a stripe-shaped second insulating film extending in the resonator length direction and having a width corresponding to the width of the stripe portion to be formed;
The groove is formed by etching the semiconductor layer using the second insulating film as a mask. At this time, the depth of the portion extending in the resonator length direction of the groove is a depth that does not reach the active layer. The depth of the portion extending in the direction perpendicular to the resonator length direction is a depth exceeding the active layer; and
And a step of growing and embedding a semiconductor layer having a band gap larger than that of the active layer inside the trench using the second insulating film as a mask.
[0010]
In the present invention, typically, the depth of the portion of the groove extending in the resonator length direction is a depth in the middle of the thickness direction of the second cladding layer, and is orthogonal to the resonator length direction of the groove. The depth of the portion extending in the direction in which the first cladding layer is formed is set to the intermediate depth in the thickness direction of the first cladding layer.
[0011]
A specific example of a semiconductor laser to which the present invention is applied is an AlGaInP semiconductor laser. In this case, for example, an AlGaAs layer, an AlGaInP layer, a ZnSe layer, or a GaN layer can be used as the semiconductor layer having a band gap larger than that of the active layer. Of these, the AlGaAs layer is superior in terms of ease of selective growth.
[0012]
According to the method of manufacturing a semiconductor laser according to the present invention configured as described above, the crystal growth is performed twice, that is, the growth of the semiconductor layer forming the laser structure and the growth of the semiconductor layer having a band gap larger than that of the active layer. Since a semiconductor laser having a window structure can be manufactured, the manufacturing process is simple. In addition, since a diffusion process is not necessary for forming the window structure, there is no problem of deterioration of element reliability. Furthermore, since a semiconductor layer having a band gap larger than that of the active layer can be used as the current confinement layer, an actual refractive index guided semiconductor laser can be manufactured.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings of the embodiments, the same or corresponding parts are denoted by the same reference numerals.
[0014]
1 to 15 show a method of manufacturing an AlGaInP semiconductor laser according to the first embodiment of the present invention. 1, 2, 4, 7, 9, 11, and 14 are sectional views in the resonator length direction, and FIGS. 5, 8, 10, 12, and 15 are the resonator lengths. Cross-sectional views perpendicular to the direction, FIGS. 3 and 6 are plan views, and FIG. 13 is a perspective view.
[0015]
In the method of manufacturing the AlGaInP semiconductor laser according to the first embodiment, first, as shown in FIG. 1, on the n-type GaAs substrate 1, for example, by a metal organic chemical vapor deposition (MOCVD) method, for example, 600 ° C. The n-type GaAs buffer layer 2, the n-type GaInP buffer layer 3, the n-type AlGaInP cladding layer 4, the active layer 5, the p-type AlGaInP cladding layer 6, the p-type GaInP intermediate layer 7 and the p-type GaAs cap layer at a growth temperature of about Grow 8 sequentially. Here, the active layer 5 may have a single quantum well (SQW) structure, for example, a multiple quantum well (MQW) structure having a GaInP layer as a well layer and an AlGaInP layer as a barrier layer, or a strained MQW structure. . Further, as the n-type GaAs substrate 1, for example, a substrate having a (100) plane orientation or a substrate having a main surface that is off, for example, 5 to 15 ° from the (100) plane is used. As an example of the thickness of each semiconductor layer, the n-type GaAs buffer layer 2 is 0.3 μm, the n-type GaInP buffer layer 3 is 0.3 μm, the n-type AlGaInP cladding layer 4 is 1 μm, and the p-type AlGaInP cladding. The layer 6 is 1 μm, the p-type GaInP intermediate layer 7 is 0.1 μm, and the p-type GaAs cap layer 8 is 0.3 μm.
[0016]
Next, as shown in FIG. 2, after an insulating film 9 such as a SiO ₂ film or a SiN _x film is formed by, for example, a CVD method, on the insulating film 9 is orthogonal to the resonator length direction by lithography. A stripe-shaped resist pattern (not shown) extending in the direction and having a predetermined width corresponding to the resonator length is formed at a pitch equal to the resonator length L, and the insulating film 9 is made, for example, reactive using this resist pattern as a mask. Etching is performed by a dry etching method such as an ion etching (RIE) method or a wet etching method. Thereafter, the resist pattern is removed. In this manner, the stripe-shaped insulating films 9 extending in the direction perpendicular to the resonator length direction and having a width 2a smaller than the resonator length L are formed at the pitch L. The planar shape of the stripe-shaped insulating film 9 is shown in FIG. Here, a is determined according to a pattern conversion difference at the next etching performed using the insulating film 9 as a mask.
[0017]
Next, as shown in FIG. 4, the n-type AlGaInP cladding layer 6 is etched to a depth in the middle of the thickness direction by, for example, a wet etching method using the stripe-shaped insulating film 9 formed as described above as a mask.
[0018]
Next, a resist pattern (not shown) having a predetermined width corresponding to the width of the stripe portion to be finally formed is formed on the stripe-shaped insulating film 9 by lithography. Thereafter, using this resist pattern as a mask, the insulating film 9 is etched by, for example, a dry etching method such as the RIE method or a wet etching method. Thereafter, the resist pattern is removed. In this way, as shown in FIG. 5, a stripe-shaped insulating film 9 extending in the cavity length direction and having a width 2b larger than the width of the stripe portion to be finally formed is finally obtained. The pitch is equal to the width of the laser chip to be formed. The planar shape of the stripe-shaped insulating film 9 is shown in FIG. Here, b is determined according to a pattern conversion difference at the next etching performed using the insulating film 9 as a mask.
[0019]
Next, as shown in FIGS. 7 and 8, a trench 10 is formed around the insulating film 9 by etching, for example, by wet etching using the stripe-shaped insulating film 9 formed as described above as a mask. To do. At the time of this etching, the depth of the portion extending in the longitudinal direction of the insulating film 9, that is, the resonator length direction in the groove 10 reaches the n-type AlGaInP cladding layer 4 (FIG. 7). The depth of the portion extending in the width direction of 9, that is, the direction orthogonal to the resonator length direction is set to a depth in the middle of the thickness direction of the p-type AlGaInP cladding layer 6 (FIG. 8).
[0020]
Next, as shown in FIGS. 9 and 10, using the insulating film 9 as a mask, an n-type AlGaAs layer 11 having a band gap larger than that of the active layer 5 is selectively grown and embedded in the trench 10 by, for example, MOCVD. . This n-type AlGaAs layer 11 is used as a current confinement layer and a window material.
[0021]
Next, after the insulating film 9 is removed by etching, as shown in FIGS. 11 and 12, for example, a Ti film, a Pt film, and an Au film are formed on the entire surface of the p-type GaAs cap layer 8 and the n-type AlGaAs layer 11 by, for example, vacuum deposition. A p-side electrode 12 is formed by sequentially forming a film, and an n-side electrode 13 is formed by sequentially forming, for example, an AuGe film and a Ni film on the back surface of the n-type GaAs substrate 1 in the same manner.
[0022]
Next, the n-type GaAs substrate 1 on which the laser structure is formed as described above is cleaved into bars to form both resonator end faces, and end face coating (not shown) is applied to these resonator end faces. After that, this bar is cleaved to make a chip. FIG. 13 shows the laser chip thus obtained. 14 and 15 are cross-sectional views of the laser chip taken along lines XIV-XIV and XV-XV, respectively. Thereafter, the laser chip thus obtained is packaged.
[0023]
The AlGaInP-based semiconductor laser manufactured in this way is an actual refractive index waveguide type because the n-type AlGaAs layer 11 serving as a current confinement layer has a larger band gap than the active layer 5.
[0024]
As described above, according to the first embodiment, the real refractive index guide having the window structure is formed by the crystal growth of the semiconductor layer for forming the laser structure and the growth of the n-type AlGaAs layer 11 twice. Since a wave-type AlGaInP-based semiconductor laser can be manufactured, the manufacturing process is simpler than the conventional method of manufacturing an AlGaInP-based semiconductor laser in which a window structure is formed by Zn diffusion, and reliability associated with Zn diffusion is improved. There is no problem of decline. In addition, since the real refractive index guided AlGaInP semiconductor laser can be manufactured, the driving current can be reduced as compared with the conventional loss guided AlGaInP semiconductor laser, and therefore, in a portion other than the end face. Can be prevented.
[0025]
As described above, for example, an AlGaInP semiconductor laser having a high output of 30 to 50 mW class and a high reliability and a long life can be realized.
[0026]
FIG. 16 shows a method of manufacturing a semiconductor laser according to the second embodiment of the present invention.
[0027]
As shown in FIG. 16, in the AlGaInP-based semiconductor laser manufacturing method according to the second embodiment, an n-type GaInP etching stop layer 14 is grown during the growth of the n-type AlGaInP cladding layer 4, and a p-type AlGaInP is grown. A p-type GaInP etching stop layer 15 is grown during the growth of the cladding layer 6. Then, the p-type GaInP etching stop layer 15 is used in the etching performed using the insulating film 9 as a mask in the step shown in FIG. 4, and the etching performed using the insulating film 9 as a mask in the steps shown in FIGS. At this time, an n-type GaInP etching stop layer 14 and a p-type GaInP etching stop layer 15 are used. Since other things are the same as those of the first embodiment, description thereof is omitted.
[0028]
According to the second embodiment, the same advantages as those of the first embodiment can be obtained, and the controllability of the etching performed using the insulating film 9 as a mask is improved, so that the manufacturing becomes easier. Have advantages.
[0029]
Next, an optical disk reproducing apparatus using the AlGaInP semiconductor laser manufactured according to the first or second embodiment as a light emitting element will be described. FIG. 17 shows the configuration of this optical disk playback apparatus.
[0030]
As shown in FIG. 17, the optical disk reproducing apparatus includes a semiconductor laser 101 as a light emitting element. As this semiconductor laser 101, the AlGaInP semiconductor laser according to the first or second embodiment described above is used. This optical disk reproducing apparatus also guides the light emitted from the semiconductor laser 101 to the optical disk D and reproduces the reflected light (signal light) from the optical disk D, that is, a collimator lens 102, a beam splitter 103, A quarter-wave plate 104, an objective lens 105, a detection lens 106, a signal light detection light receiving element 107, and a signal light reproduction circuit 108 are provided.
[0031]
In this optical disk reproducing apparatus, the emitted light L of the semiconductor laser 101 is converted into parallel light by the collimator lens 102, and further, the degree of polarization is adjusted by the quarter wavelength plate 104 through the beam splitter 103, and then by the objective lens 105. The light is condensed and incident on the optical disk D. Then, the signal light L ′ reflected by the optical disk D is reflected by the beam splitter 103 through the objective lens 105 and the quarter wavelength plate 104, and then enters the light receiving element 107 for detecting signal light through the detection lens 106. Here, after being converted into an electric signal, the information written on the optical disk D is reproduced in the signal light reproducing circuit 108.
[0032]
Here, the case where the AlGaInP semiconductor laser according to the first or second embodiment described above is applied to a light emitting element of an optical disk reproducing device has been described, but the present invention is applied to an optical disk recording / reproducing device or a light emitting element of an optical disk recording device. Of course, the present invention can also be applied to a light emitting element of an optical device such as an optical communication device or a light emitting element of an in-vehicle device that needs to be operated at a high temperature.
[0033]
As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, The various deformation | transformation based on the technical idea of this invention is possible.
[0034]
For example, the numerical values, structures, processes, and the like given in the first and second embodiments are merely examples, and different numerical values, structures, processes, and the like may be used as necessary.
[0035]
【The invention's effect】
As described above, according to the method of manufacturing a semiconductor laser according to the present invention, a semiconductor laser having a window structure and a real refractive index waveguide type can be obtained by a simple process without reducing the reliability of the element. Can be manufactured.
[Brief description of the drawings]
FIG. 1 is a sectional view in a cavity length direction for explaining a method of manufacturing an AlGaInP-based semiconductor laser according to a first embodiment of the invention.
FIG. 2 is a cross-sectional view in the cavity length direction for explaining the method of manufacturing the AlGaInP semiconductor laser according to the first embodiment of the invention.
FIG. 3 is a plan view for explaining the method for manufacturing the AlGaInP-based semiconductor laser according to the first embodiment of the invention.
FIG. 4 is a cross-sectional view in the cavity length direction for explaining the method of manufacturing the AlGaInP-based semiconductor laser according to the first embodiment of the invention.
FIG. 5 is a cross-sectional view perpendicular to the cavity length direction for explaining the method of manufacturing the AlGaInP semiconductor laser according to the first embodiment of the invention.
FIG. 6 is a plan view for explaining the method for manufacturing the AlGaInP-based semiconductor laser according to the first embodiment of the invention.
FIG. 7 is a sectional view in the cavity length direction for explaining the method of manufacturing the AlGaInP-based semiconductor laser according to the first embodiment of the invention.
FIG. 8 is a cross-sectional view perpendicular to the cavity length direction for explaining the method of manufacturing the AlGaInP semiconductor laser according to the first embodiment of the invention.
FIG. 9 is a sectional view in the cavity length direction for explaining the method of manufacturing the AlGaInP-based semiconductor laser according to the first embodiment of the invention.
FIG. 10 is a cross-sectional view perpendicular to the cavity length direction for explaining the method of manufacturing the AlGaInP semiconductor laser according to the first embodiment of the invention.
11 is a sectional view in the cavity length direction for explaining the method of manufacturing the AlGaInP-based semiconductor laser according to the first embodiment of the invention. FIG.
FIG. 12 is a cross-sectional view perpendicular to the cavity length direction for explaining the method of manufacturing the AlGaInP semiconductor laser according to the first embodiment of the invention.
FIG. 13 is a perspective view showing an AlGaInP-based semiconductor laser manufactured according to the first embodiment of the present invention.
14 is a cross-sectional view taken along line XIV-XIV of the AlGaInP-based semiconductor laser shown in FIG.
15 is a sectional view taken along line XV-XV of the AlGaInP-based semiconductor laser shown in FIG.
FIG. 16 is a cross-sectional view in the cavity length direction for explaining the method of manufacturing the AlGaInP semiconductor laser according to the second embodiment of the invention.
FIG. 17 is a schematic diagram showing an optical disk reproducing apparatus using an AlGaInP semiconductor laser manufactured according to the first or second embodiment of the present invention as a light emitting element;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... n-type GaAs substrate, 4 ... n-type AlGaInP clad layer, 5 ... Active layer, 6 ... p-type AlGaInP clad layer, 7 ... p-type GaInP intermediate layer, 8 ... p-type GaAs cap layer, 9 ... insulating film, 10 ... groove, 11 ... n-type AlGaAs layer, 12 ... p-side electrode, 13 ... n-side electrode, 14 ... n-type GaInP etching stop layer, 15... P-type AlGaInP etching stop layer

Claims (4)

Growing a semiconductor layer forming a laser structure on the substrate, the first layer including a first conductivity type first clad layer, an active layer, and a second conductivity type second clad layer;
Forming a stripe-shaped first insulating film extending in a direction perpendicular to the resonator length direction and having a width corresponding to the resonator length on the semiconductor layer;
Etching the semiconductor layer to a depth that does not reach the active layer using the first insulating film as a mask;
Patterning the first insulating film to form a stripe-shaped second insulating film extending in the resonator length direction and having a width corresponding to the width of the stripe portion to be formed;
The groove is formed by etching the semiconductor layer using the second insulating film as a mask. At this time, the depth of the portion extending in the resonator length direction of the groove is a depth that does not reach the active layer. The depth of the portion extending in the direction orthogonal to the resonator length direction in the groove is to be greater than the active layer;
A step of growing and embedding a semiconductor layer having a band gap larger than that of the active layer in the trench using the second insulating film as a mask.
A method of manufacturing a semiconductor laser. The depth of the portion extending in the resonator length direction of the groove is the depth in the middle of the thickness direction of the second cladding layer, and the portion of the groove extending in the direction orthogonal to the resonator length direction is 2. The method of manufacturing a semiconductor laser according to claim 1, wherein the depth is a depth in the middle of the thickness direction of the first cladding layer. 2. The method of manufacturing a semiconductor laser according to claim 1, wherein the semiconductor laser is an AlGaInP semiconductor laser. 4. The method for manufacturing a semiconductor laser according to claim 3, wherein the semiconductor layer having a band gap larger than that of the active layer is an AlGaAs layer, an AlGaInP layer, a ZnSe layer, or a GaN layer.

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