JP2007012851A - Method of manufacturing semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a high output semiconductor laser device with good laser characteristics. <P>SOLUTION: In the method of manufacturing the semiconductor laser device having a pair of resonator faces which are made of AlGaAs based semiconductor material and parallel to one another, and an impurity diffusion area which is formed in the vicinity of the resonator face, after a ridge 10 is formed, impurities are diffused from an upper face side of the ridge 10 in the vicinity of the resonator faces A, B, to form impurity diffusion areas Za, Zb, and an active layer 4 in the impurity diffusion areas Za, Zb is sufficiently made disordered. Thereafter, a second current narrow layer 15b made of GaAs is removed in the impurity diffusion areas Za, Zb. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a high-power semiconductor laser device used in an optical disk drive or the like.

The semiconductor laser element is used for recording / reproduction of video, music, and other digital information as well as optical communication. In particular, a high-power semiconductor laser element of, for example, 30 mW or more is used as a writing light source for an optical disk drive.
However, a high-power semiconductor laser device is liable to cause optical damage called COD (Catastrophic Optical Damage), and there is a problem that the reliability of the semiconductor laser device is lowered due to this optical damage.
This COD is generated when the vicinity of the resonator surface of the active layer is an absorption region for the laser light generated in the active layer inside the device.
In the element manufacturing process, usually, a wafer that has undergone a predetermined process is cleaved to obtain a plurality of semiconductor laser elements whose cleaved surfaces serve as resonator surfaces. At that time, since the cleavage is performed in the atmosphere, the vicinity of the surface including the resonator surface reacts with oxygen in the atmosphere to become a natural oxide layer.
Since the band gap of the active layer in this natural oxide layer is narrower than the band gap of the active layer inside the device, it becomes a laser light absorption region, and the temperature of the active layer in the natural oxide layer rises. This temperature rise further narrows the band gap of the active layer in the natural oxide layer, and the absorption of laser light is more likely to occur. As a result, the temperature of the active layer in the natural oxide layer continues to rise, and finally the cavity surface melts, destroying the semiconductor laser element.

  As a method for preventing the generation of COD, the active layer in the semiconductor laser device is disordered in the vicinity of the resonator surface, thereby making the band gap in the vicinity of the resonator surface of the active layer wider than that in the active layer inside the device. There is a way to do it. Patent Document 1 describes an example of a semiconductor laser element having a window structure in which absorption of laser light in the vicinity of the resonator surface is reduced by this method.

The feature of the invention described in Patent Document 1 is that the Zn concentration of the second p-type cladding layer is set to a high concentration of 5E18 cm ⁻³ or more, and the vicinity of the surface including the resonator surface is formed before the ridge is formed. Zn is diffused in the portion to disorder the surface vicinity including the resonator surface in the active layer.

First, as a conventional example, a method for manufacturing a semiconductor laser device 100 as described in Patent Document 1 will be described with reference to FIGS. 10 to 12 are perspective views for explaining a method for manufacturing the semiconductor laser device 100. FIG.
Note that an n-type substrate 101 described below has a plurality of semiconductor laser elements 100 formed in a matrix, and a single semiconductor laser is obtained by cleaving and dividing the n-type substrate 101 at a predetermined interval. Although the element 100 can be obtained, FIGS. 10 to 12 show the structure of the single semiconductor laser element 100 from the beginning of the process for easy understanding of the description.

First, as shown in FIG. 10, on an n-type substrate 101 made of GaAs, an n-type buffer layer 102 made of GaAs, an n-type clad layer 103 made of AlGaAs, an active layer 104, and a first p-type clad made of AlGaAs. A layer 105, a p-type etching stop layer 106 made of GaInP, a second p-type cladding layer 107 made of AlGaAs and having a Zn (zinc) concentration of 5E18 cm ⁻³ or more, and a p-type cap layer 108 made of GaInP. .
Next, a diffusion source layer 109 made of GaAs containing Zn as an impurity is formed in a substantially parallel stripe pattern on the surface of the p-type cap layer 108 that becomes the resonator surfaces Aa and Ba. Here, the resonator surface Aa indicates the entire front surface in FIG. 10, the resonator surface Ba indicates the entire surface opposite to the resonator surface Aa, and the resonator surface Aa and the resonator surface Ba are mutually connected. Parallel.
Next, Zn in the diffusion source layer 109 is selectively annealed in a region from the diffusion source layer 109 toward the n-type substrate 101, passing through the active layer 104, and halfway through the n-type cladding layer 103. Spread.
In FIG. 10, the regions Ze and Zf in which Zn is diffused are represented by a shaded range for easy understanding.

  Next, as shown in FIG. 11, the diffusion source layer 109 is removed, and a part of the second p-type cladding layer 107 and the p-type cap layer 108 are removed by etching using a photolithographic method. Ridges 110 extending in a direction orthogonal to Aa and Ba are formed in parallel stripes having a predetermined interval. In FIG. 11, one of the ridges 110 is shown.

  Further, as shown in FIG. 12, an n-type block layer 111 made of AlGaAs, a p-type contact layer 112 made of GaAs, and a p-type electrode 113 are sequentially stacked on the etching stop layer 106 and the ridge 110 to form an n-type. An n-type electrode 114 is formed on the surface of the substrate 101 opposite to the above-described stacking direction.

The n-type substrate 101 that has undergone the above-described steps is cleaved along a plane that bisects the Zn diffusion regions Ze and Zf in the extending direction, thereby obtaining a bar (not shown). The cleavage planes become resonator planes Aa and Ba of the semiconductor laser element 100 described later.
Next, the bar is divided by a plane that passes through the center line between the ridges 110 formed in a stripe shape and is orthogonal to the surface of the n-type substrate 101, thereby obtaining the semiconductor laser device 100 of the conventional example.

A forward current is injected into the semiconductor laser element 100 from the p-type electrode 113 side to the n-type electrode 114 side. When this current exceeds the oscillation threshold, laser oscillation occurs in the active layer 104 corresponding to the lower portion of the ridge 110, and laser light is emitted from one of the resonator surfaces Aa and Ba of the active layer 104. The
JP 2004-288894 A

  However, the above-described conventional method for manufacturing the semiconductor laser device 100 has the following problems.

In the conventional example, Zn diffusion is performed before the ridge 110 is formed, and the portions near the resonator planes Aa and Ba of the active layer 104 are disordered. At this time, in order to sufficiently perform disordering, it is necessary to raise the annealing temperature or lengthen the annealing time. However, under such Zn diffusion conditions, disordering of the etching stop layer 106 is also promoted. Further, the etching stop layer 106 is connected to the adjacent first p-type cladding layer 105 and the second p-type cladding layer 107. Since the mixed crystal is formed, the etching resistance of the etching stop layer is deteriorated.
When the etching resistance is deteriorated, the etching stop layer 106 cannot be stopped in the etching for forming the ridge 110, and a part of the first p-type cladding layer 105 is removed. As described above, the semiconductor laser device 100 from which a part of the first p-type cladding layer 105 is removed has a problem that the laser characteristics are deteriorated, for example, the light emission efficiency is lowered, depending on the degree of the removal.

  Accordingly, an object of the present invention is to provide a method for manufacturing a high-power semiconductor laser device having good laser characteristics.

In order to solve the above problems, each invention of the present application has the following procedure as means.
1) A pair of resonator surfaces (A, B) made of an AlGaAs semiconductor material and parallel to each other, and impurity diffusion regions (Za, Zb) formed in the vicinity of the resonator surfaces (A, B) In the method of manufacturing a semiconductor laser device (50) having, at least a first conductivity type cladding layer (3), an active layer (4), a first second conductivity type cladding on a first conductivity type semiconductor substrate (1). Lamination for forming a laminated substrate in which a layer (5), a second conductivity type etching stop layer (6), a second second conductivity type cladding layer (7) and a second conductivity type cap layer (8) are laminated in this order. And a step of selectively etching the second conductivity type cap layer (8) and the second second conductivity type cladding layer (7) to thereby form substantially parallel stripe-shaped ridges (10) having a predetermined interval. Ridge forming step of forming a A first first-conductivity-type current confinement layer (15a) made of AlGaAs is formed on the surface of the conductive-type etching stop layer (6). Further, the first first-conductivity-type current confinement layer (15a) and the above-mentioned A constriction layer forming step of laminating a second first conductivity type current confinement layer (15b) made of GaAs on the surface of the ridge (10), and the second first conductivity type current corresponding to the ridge (10) A diffusion source layer forming step of forming a diffusion source layer (12) having impurities on the constriction layer (15b) in a substantially parallel stripe shape having a predetermined interval with respect to the direction in which the ridge (10) extends. Then, the impurity is diffused by annealing, and the impurity diffusion region (Za) is formed in a region from the second first conductivity type current confinement layer (15b) to the middle of the first conductivity type cladding layer (3). , Zb) diffusion And a removal step for removing at least the second first-conductivity-type current confinement layer (15b) in the impurity diffusion regions (Za, Zb) in this order. 50).

  According to the present invention, after the ridge is formed, the impurity is diffused in the active layer in the vicinity of the surface including the resonator surface and disordered as the impurity diffusion region, and then the second region made of at least GaAs in the impurity diffusion region. By removing the current confinement layer, it is possible to obtain a high-power semiconductor laser device with good laser characteristics.

Embodiments of the present invention will be described with reference to FIGS.
FIG. 1 is a perspective view for explaining a first step of an embodiment in the method for manufacturing a semiconductor laser device of the present invention.
FIG. 2 is a perspective view for explaining a second step of the embodiment in the method for manufacturing a semiconductor laser device of the present invention.
FIG. 3 is a perspective view for explaining a third step of the embodiment in the method for manufacturing a semiconductor laser device of the present invention.
FIG. 4 is a perspective view for explaining a fourth step of the embodiment in the method for manufacturing a semiconductor laser device of the present invention.
FIG. 5 is a perspective view for explaining a fifth step of the embodiment in the method for manufacturing a semiconductor laser device of the present invention.
FIG. 6 is a perspective view for explaining a sixth step of the embodiment in the method for manufacturing a semiconductor laser device of the present invention.
FIG. 7 is a perspective view for explaining the seventh step of the embodiment in the method for manufacturing a semiconductor laser device of the present invention.
FIG. 8 is a perspective view for explaining an eighth step of the embodiment in the method for manufacturing a semiconductor laser device of the present invention.
FIG. 9 is a perspective view for explaining a ninth step of the embodiment in the method for manufacturing a semiconductor laser element of the present invention.

An n-type substrate 1 to be described below has a plurality of semiconductor laser elements 50 formed in a matrix. By cleaving and dividing the n-type substrate 1 at a predetermined interval, a single semiconductor laser element 50 is formed. 1 to 9, the structure of a single semiconductor laser element 50 is shown from the beginning of the process for easy understanding of the description.
Examples of the method for manufacturing a semiconductor laser device of the present invention will be described below.
In the conventional example, Zn diffusion is performed before ridge formation, whereas in this embodiment, Zn diffusion is performed after ridge formation.

(First step) [See FIG. 1]
On an n-type substrate 1 made of GaAs, an n-type clad layer 3 made of AlGaAs 3, an active layer 4, a first p-type clad layer 5 made of AlGaAs, an etching stop layer 6, and a second p-type clad layer made of AlGaAs 7 and a p-type cap layer 8 made of GaAs are sequentially stacked by metal organic vapor phase epitaxy (MOVPE).
The etching stop layer 6 is provided so that the first p-type cladding layer 5 is not damaged by etching due to etching for forming the ridge 10 described later.

Next, on the surface of the p-type cap layer 8, an etching mask layer 9 made of, for example, SiO ₂ (silicon dioxide) and extending in a direction perpendicular to the surfaces to be the resonator surfaces A and B is substantially parallel. The stripe is formed.
Here, the resonator surface A indicates the entire front surface in FIG. 1, the resonator surface B indicates the entire surface opposite to the resonator surface A, and the resonator surface A and the resonator surface B are mutually connected. Parallel.

(Second step) [See FIG. 2]
By etching away the second p-type cladding layer 7 and the p-type cap layer 8 corresponding to the range not protected by the etching mask layer 9, the second p-type cladding layer 7 and the p-type cap layer 8 are removed. The ridge 10 is formed in a substantially parallel stripe shape having a predetermined interval.
At this stage, since the etching stop layer 6 is not annealed to deteriorate the etching resistance as shown in the conventional example, the etching stop layer 6 has sufficient etching resistance when the ridge 10 is formed. is doing. Therefore, the above-described etching stops at this etching stop layer 6, and therefore the first p-type cladding layer 5 is not etched.

(Third step) [See FIG. 3]
A first n-type current confinement layer 15a made of AlGaAs is formed on the surface of the etching stop layer 6 so as to have a predetermined thickness.
Further, a second n-type current confinement layer 15 b made of GaAs is formed on the surfaces of the first n-type current confinement layer 15 a and the ridge 10.

(4th process) [Refer FIG. 4]
Extending in the direction perpendicular to the extending direction of the ridge 10 on the resonator surface A, B side of the surface of the second n-type current confinement layer 15b, ZnO (zinc oxide) and SiO ₂ (silicon dioxide) Are formed in a substantially parallel stripe shape.
Thereafter, the SiO ₂ layer 13 is formed on the surfaces of the diffusion source layer 12 and the second n-type current confinement layer 15b. This SiO ₂ layer 13 is formed to prevent evaporation of Zn during Zn diffusion described later.

(Fifth step) [Refer to FIG. 5]
By annealing, the impurities in the diffusion source layer 12 are formed in a region from the diffusion source layer 12 toward the n-type substrate 1, passing through the etching stop layer 6 and the active layer 4 and halfway through the n-type cladding layer 3. Diffusion regions Za and Zb are formed by diffusing Zn (zinc).
In FIG. 5, the diffusion regions Za and Zb are represented by a shaded area for easy understanding.

  In this annealing, annealing conditions are set so that the active layers 4 in the diffusion regions Za and Zb are sufficiently disordered. In order for the active layer 4 in the diffusion regions Za and Zb to be sufficiently disordered, Zn may be diffused into the active layer 4 by increasing the annealing temperature or extending the annealing time. In this example, the annealing temperature was set to 625 ° C. and the annealing time was set to 50 minutes.

Further, the annealing conditions are not limited to the present embodiment. As a result of intensive studies by the inventors, if the difference between the photoluminescence wavelength of the active layer 4 in the diffusion regions Za and Zb and the photoluminescence wavelength of the active layer 4 in regions other than the diffusion regions Za and Zb is 40 nm or more It has been found that the active layer 4 in the diffusion regions Za and Zb is sufficiently disordered.
Therefore, the annealing conditions may be set so that the above-described difference in photoluminescence wavelength is 40 nm or more. Specifically, the above-described difference in photoluminescence wavelength can be increased by increasing the annealing temperature or increasing the annealing time. However, when the annealing temperature exceeds 800 ° C., Zn diffusion from the first p-type cladding layer 5 adjacent to the active layer 4 to the active layer 4 occurs, and the active layer 4 in regions other than the diffusion regions Za and Zb also It will be disordered. If the active layer 4 in the region other than the diffusion regions Za and Zb is disordered, the manufactured semiconductor laser device will not oscillate.
Therefore, it is necessary to set the annealing temperature to 800 ° C. or lower.

  By the way, since the etching stop layer 6 is disordered by this annealing, the etching resistance of the etching stop layer 6 is deteriorated, but the ridge 10 forming process that requires etching resistance has already been completed. There is no problem.

(Sixth step) [Refer to FIG. 6]
After removing the SiO ₂ layer 13 and the diffusion source layer 12, the upper portion of the second n-type current confinement layer 15b is removed so that the upper surface of the ridge 10 is exposed.
Next, a p-type contact layer 16 made of GaAs is formed on the surfaces of the ridge 10 and the second n-type current confinement layer 15b.

(Seventh step) [Refer to FIG. 7]
A resist 18 is formed in parallel stripes by photolithography on the surface of the p-type contact layer 16 corresponding to a range that completely covers the diffusion regions Za and Zb.
Next, a metal layer 19 to be a P-type electrode 20 described later is formed on the surfaces of the resist 18 and the p-type contact layer 16.
Further, the n-type electrode 21 is formed on the surface of the n-type substrate 1 opposite to the above-described lamination direction.

(Eighth step) [Refer to FIG. 8]
The resist 18 and the metal layer 19 on the resist 18 are removed by a lift-off method such as ultrasonic cleaning using a solvent. The metal layer 19 that has not been removed becomes the P-type electrode 20.

(9th step) [Refer to FIG. 9]
Using the P-type electrode 20 as an etching mask, the p-type contact layer 16, the second n-type current confinement layer 15b in the diffusion regions Za and Zb, and the diffusion regions Za and Zb corresponding to the range not covered with the P-type electrode 20 The p-type cap layer 8 is removed by etching with, for example, an ammonia hydrogen peroxide aqueous etching solution.

Next, the n-type substrate 1 that has undergone the above-described steps is cleaved along a plane that bisects the diffusion regions Za and Zb in a direction in which the diffusion regions Za and Zb extend, and a bar (not shown) whose cleaved surfaces become the resonator surfaces A and B. Z).
This bar is divided by a plane that passes through the center line between the ridges 10 formed in a stripe shape and is orthogonal to the surface of the n-type substrate 1 that has undergone the above-described steps, thereby obtaining the semiconductor laser device 50 of this embodiment.

  A forward current is injected into the semiconductor laser element 50 from the p-type electrode 20 side toward the n-type electrode 21 side. When this current exceeds the oscillation threshold, laser oscillation occurs in the active layer 4 corresponding to the lower portion of the ridge 10, and laser light is emitted from one of the resonator surfaces A and B of the active layer 4. The

Here, the reason why the above-described layer portions are removed by etching in the ninth step will be described below.
In general, Zn diffuses more easily in GaAs than in AlGaAs. Accordingly, Zn is diffused at a higher concentration in the second n-type current confinement layer 15b made of GaAs than in the first n-type current confinement layer 15a made of AlGaAs by Zn diffusion in the fifth step. For example, the Zn concentration of the first n-type current confinement layer 15a in the diffusion regions Za and Zb is 1 to 3E18 cm ⁻¹ , whereas the Zn of the second n-type current confinement layer 15b in the diffusion regions Za and Zb is The concentration is 1E19 cm ⁻¹ or higher.
As described above, when a current is passed through the semiconductor laser element having the second n-type current confinement layer 15b having the diffusion regions Za and Zb in which Zn is diffused at a high concentration, the second of the diffusion regions Za and Zb is supplied. A reactive current flows through the element through the n-type current confinement layer 15b. Therefore, the light emission efficiency of such a semiconductor laser device is lowered.
For the reason described above, in the ninth step, the second n-type current confinement layer 15b in the diffusion regions Za and Zb is removed by etching.

  In addition, the ammonia hydrogen peroxide aqueous etchant used in the ninth step has a higher etching rate for GaAs than that for AlGaAs, so that the second n-type current confinement layer 15b made of GaAs is selectively etched. However, the p-type contact layer 16 made of GaAs and the p-type cap layer 8 made of GaAs are also etched by this etching.

  The embodiment of the present invention is not limited to the configuration and procedure described above, and it goes without saying that modifications may be made without departing from the scope of the present invention.

It is a perspective view for demonstrating the 1st process of the Example in the manufacturing method of the semiconductor laser element of this invention. It is a perspective view for demonstrating the 2nd process of the Example in the manufacturing method of the semiconductor laser element of this invention. It is a perspective view for demonstrating the 3rd process of the Example in the manufacturing method of the semiconductor laser element of this invention. It is a perspective view for demonstrating the 4th process of the Example in the manufacturing method of the semiconductor laser element of this invention. It is a perspective view for demonstrating the 5th process of the Example in the manufacturing method of the semiconductor laser element of this invention. It is a perspective view for demonstrating the 6th process of the Example in the manufacturing method of the semiconductor laser element of this invention. It is a perspective view for demonstrating the 7th process of the Example in the manufacturing method of the semiconductor laser element of this invention. It is a perspective view for demonstrating the 8th process of the Example in the manufacturing method of the semiconductor laser element of this invention. It is a perspective view for demonstrating the 9th process of the Example in the manufacturing method of the semiconductor laser element of this invention. It is a perspective view for demonstrating the manufacturing method of the semiconductor laser element of a prior art example. It is a perspective view for demonstrating the manufacturing method of the semiconductor laser element of a prior art example. It is a perspective view for demonstrating the manufacturing method of the semiconductor laser element of a prior art example.

Explanation of symbols

1 n-type substrate, 3 n-type cladding layer, 4 active layer, 5 first p-type cladding layer, 6 etching stop layer, 7 second p-type cladding layer, 8 p-type cap layer, 9 etching mask layer, 10 Ridge, 12 diffusion source layer, 13 SiO ₂ layer, 15a, 15b current confinement layer, 16 p-type contact layer, 18 resist, 19 metal layer, 20 p-type electrode, 21 n-type electrode, 50 semiconductor laser element, A, B Cavity plane, Za, Zb diffusion region

Claims (1)

In a method of manufacturing a semiconductor laser device comprising an AlGaAs-based semiconductor material and having a pair of parallel resonator surfaces and an impurity diffusion region formed in the vicinity of the resonator surface,
On the first conductivity type semiconductor substrate, at least a first conductivity type cladding layer, an active layer, a first second conductivity type cladding layer, a second conductivity type etching stop layer, a second second conductivity type cladding layer, and a first A laminating step of forming a laminated substrate in which two conductive type cap layers are laminated in this order;
A ridge forming step of forming substantially parallel stripe-shaped ridges having a predetermined interval by selectively etching the second conductivity type cap layer and the second second conductivity type cladding layer;
A first conductivity type current confinement layer made of AlGaAs is formed on the surface of the second conductivity type etching stop layer, and further, GaAs is formed on the surfaces of the first first conductivity type current confinement layer and the ridge. A constriction layer forming step of laminating a second first-conductivity-type current confinement layer comprising:
On the second first-conductivity-type current confinement layer corresponding to the ridge, a diffusion source layer having impurities is formed in a substantially parallel stripe shape having a predetermined interval with respect to the direction in which the ridge extends. A diffusion source layer forming step;
A diffusion step of diffusing the impurity by annealing to form the impurity diffusion region in a region from the second first conductivity type current confinement layer to the middle of the first conductivity type cladding layer;
A method of manufacturing a semiconductor laser device, comprising at least a removal step of removing the second first-conductivity-type current confinement layer in the impurity diffusion region in this order.

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