JP2723649B2 - Method for manufacturing semiconductor laser device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an edge-emitting semiconductor laser device which exhibits high reliability even when operated for a long time in a high output state.

(Prior Art) An edge-emitting type semiconductor laser device is a typical semiconductor device utilizing cleavage of a semiconductor crystal, and is composed of a Fabry-Perot-type cavity comprising a set of semiconductor mirror surfaces based on a refractive index difference between the semiconductor crystal and air. It has a vessel.

At present, it is widely used as a light source for such edge-emitting semiconductor laser devices and optical disk devices. In particular, when these semiconductor laser devices are used as light sources in writable write-once optical disc devices or erasable rewritable optical disc devices, high reliability is required even in the high power state of about 40 to 50 mW. Is done. In addition, there is a demand for a semiconductor laser device capable of obtaining a higher light output for the purpose of increasing the operation speed of the entire system including the optical disk device. When used as a light source for a high-definition laser printer device or an excitation light source for a solid-state laser device such as a YAG laser, a high-output semiconductor laser element having a high output of 100 mW or more is required.

However, the edge-emitting semiconductor laser device has a problem that its edge face gradually deteriorates when operated in a high output state. When the end face is deteriorated, the driving current increases, and eventually laser oscillation does not occur. Therefore, it was difficult to obtain high reliability in a high output state.

Such end face deterioration is caused by the following causes. First, since the light density at the exit facet is high and non-radiative recombination occurs via the surface level, local heat generation occurs near the facet. When the temperature near the end face increases, the heat reduces the forbidden band width in the area near the end face and increases light absorption. The carriers generated thereby recombine non-radiatively through the surface states, so that more heat is generated. As this process is repeated, the temperature of the semiconductor crystal near the end face increases, eventually reaches the melting point, and the end face is destroyed.

The present inventors have proposed that an inclined bandgap layer be provided on a cleavage plane of a semiconductor crystal to be an end face of a cavity as means for suppressing end face degradation in an end face emission type semiconductor laser device (Japanese Patent Application No. Hei. No. 60422).

This inclined bandgap layer has a forbidden band width that gradually increases as the distance from the cleavage plane increases. Therefore, the carriers generated near the end face not only move by diffusion but also are strongly drawn into the semiconductor crystal by the drift caused by the slope of the forbidden band width, and the probability that the surface state near the end face is captured is extremely high. Become smaller. Furthermore, since the forbidden band width of the inclined band gap layer is larger than the laser excitation portion including the active layer, light absorption near the end face is reduced. As a result, end face deterioration is effectively suppressed, and reliability in a high output state is improved.

However, if the cleavage of the semiconductor crystal is performed in the air, the cleavage plane is oxidized. Therefore, there is a problem that it is difficult to form the inclined bandgap layer on the cleavage plane.

Therefore, as a method of manufacturing such an edge-emitting semiconductor laser device, a projection is formed by etching on a semiconductor crystal constituting a laminated structure on a substrate, and the projection is formed under an atmosphere substantially free of oxygen. A method is conceivable in which a cavity is formed by applying a force to the protrusion to cleave it (microcleave method), and then a graded bandgap layer is formed on the cleavage plane.

Heretofore, an edge-emitting semiconductor laser device having such a forbidden band gap layer has been manufactured as follows.
Here, as an example, a case of a GaAs-based or GaAlAs-based edge-emitting semiconductor laser device will be described.

First, a GaAs active layer or GaAlAs is formed on a GaAs substrate 11 by using a known growth method such as a liquid phase growth method or a vapor phase growth method.
A laminated structure 13 including the active layer 12 is formed. Next, an SiO ₂ film 19 is formed on the surface of the laminated structure 13 by using a plasma CVD method. Then, after a photoresist is applied to the entire surface of the SiO ₂ film 19, a predetermined resist pattern is formed by using a photolithography method. Using this resist pattern as a mask, by etching the SiO ₂ film 19, SiO ₂ film 19 as a shaded area in FIG. 4 to suit the laser excitation unit 20
To form

Next, as shown by the thick arrow in FIG. 5, the substrate 11 and the laminated structure 13 are obliquely formed by ion milling.
Is etched to form a projection 21.

FIG. 6 (a) shows the XX 'section and the YY' section of the protrusion 21 of FIG. 5 together. FIG. 6 (b) shows a section taken along the line ZZ 'of the protrusion 21 in FIG. Since the etching is performed in an oblique direction, the cross-sectional shape of the protrusion 21 becomes a triangle. The protruding part 21 is a connecting part 22 and
It is only connected to 13, and its bottom is separated from substrate 11. The cross-sectional shape of the connecting portion 22 is also triangular, but smaller than the projecting portion 21.

The substrate 11 on which the protrusions 21 are formed is put into a vapor phase growth apparatus such as an organic metal pyrolyzer or a molecular beam epitaxy apparatus, and is placed under an atmosphere substantially free of oxygen (for example, under vacuum, under nitrogen, Atmosphere or hydrogen atmosphere)
In the cleavage step. By this cleavage, a resonator is formed, and the cleavage plane 23 becomes the end face.

(Problem to be Solved by the Invention) In the above cleavage step, the cross section of the connecting portion 22
The projection 21 is easily cleaved at the connecting portion 22 by applying a slight force. In addition, since the cleavage is performed in an atmosphere substantially free of oxygen, the cleavage plane 23 is not oxidized, and thus the inclined bandgap layer 16 can be easily formed on the cleavage plane 23.

However, in such a method, cleavage must be performed by applying a force one by one in a vapor phase epitaxy apparatus by remote operation. Therefore, a very long time is required. The substrate may be damaged.

The present invention solves the above-mentioned conventional problems,
The purpose is to cleave the protrusions formed on the substrate easily and in a short time. Moreover, without exposing the cleavage plane to oxygen, an inclined bandgap layer is formed on this cleavage plane. An object of the present invention is to provide a method capable of easily forming a high-output edge-emitting semiconductor laser device with high yield.

(Means for Solving the Problems) A method for manufacturing a semiconductor laser device according to the present invention is a method for manufacturing an edge-emitting semiconductor laser device in which a laminated structure including an active layer is formed on a substrate. Forming a protrusion on the semiconductor crystal to be formed; applying ultrasonic vibration in a solution of a sulfur-containing compound to cleave the protrusion to form a resonator end face and protecting the resonator end face containing sulfur. Forming a film, whereby the above object is achieved.

Preferably, the method further includes a step of forming a semiconductor layer having a forbidden band width larger than the forbidden band width of the active layer on the end face of the resonator.

(Function) As described above, when ultrasonic vibrations are applied in the sulfur-containing compound solution to cleave the protrusions, ultrasonic vibrations are also applied to the sulfide-containing solution, so that a protective film is formed on the cleavage surface. Is done.

Therefore, according to the present invention, since the oxidation of the cleavage plane is reliably prevented by the protective film, the cleavage plane is not oxidized by oxygen in the air.

As a result, according to the present invention, a highly reliable semiconductor laser device without end face degradation can be realized.

Further, according to the structure further including the step of forming a semiconductor layer having a forbidden band width larger than the forbidden band width of the active layer on the end face of the resonator, the semiconductor layer can be formed on a clean interface.

As a result, a good interface is formed between the stacked structure including the active layer and the semiconductor layer, so that an edge-emitting semiconductor laser device having high reliability even in a high output state can be obtained.

(Example) An example of the present invention will be described below.

FIG. 1 shows an embodiment of an edge-emitting semiconductor laser device obtained by the manufacturing method of the present invention. This figure shows only the emission end face side of the semiconductor laser device having the following structure.

First, a GaAs or GaAlAs active layer is formed on the GaAs substrate 11.
A laminated structure 13 including 12 is formed. On the upper surface of the multilayer structure 13 and the lower surface of the GaAs substrate 11, electrodes 14 and
15 are provided. An inclined bandgap layer 16 is formed at least on the end face of the resonator on the emission side, and an end face reflection film is formed on the surface thereof. When the forbidden bandgap layer 16 is formed only on the end face of the cavity on the emission side, an end face reflection film 17 having a low reflectance is formed on the surface of the forbidden bandgap layer 16. On the other end face of the resonator, an end face reflection film 18 (not shown in FIG. 1) having a high reflectance is formed.

The edge-emitting semiconductor laser device having such a structure was manufactured as follows. Since the steps up to the step of forming the projection 21 to be cleaved on the substrate 11 are the same as those in the above-described conventional case, the subsequent steps are described below with reference to FIGS. 2 (a) and 2 (b) and FIG. 3 (a) ~
This will be described with reference to FIG. However, in FIGS. 3A to 3E, the GaAs active layer or the GaAlAs active layer 12 is formed.
The illustration of the laminated structure 13 including is omitted. As a method for forming the projection, a selective etching method (see Appl. Phys. Lett., 40 , 289 (1982)) may be used in addition to the above method.

First, as shown in FIG. 2 (a), the substrate 11 on which the protrusions 21 are formed as shown in FIG. 3 (a) is put into a beaker 25 containing a sulfur-containing compound (for example, (NH ₄ ) ₂ ). S, (NH ₄ )
₂ S _x , or Na ₂ S). And the second
As shown in FIG. 2B, the beaker 25 was placed in the water tank 28 of the ultrasonic cleaner 27, and the substrate 11 was subjected to ultrasonic vibration. As a result, as shown in FIG. 3 (b), the protruding portion 21 of the substrate 11 was immediately cleaved at the connecting portion 22, and a resonator was formed. The cleavage plane 23 formed at this time becomes the cavity end face. Substrate 11
The protrusions 21 separated from the sulfur-containing compound solution 26 are left in the sulfur-containing compound solution 26, and only the substrate 11 as shown in FIG. 3 (c) is taken out from the sulfur-containing compound solution 26 and quickly dried by blowing nitrogen gas. , And introduced into the organometallic pyrolysis unit.

In the organometallic thermal decomposition apparatus, as shown in FIG. 3 (d), the inclined bandgap layer 16 made of Ga _1-x Al _x As
And formed on the bottom and side surfaces of the stripe groove containing. The Al mixed crystal ratio x of the inclined bandgap layer 16 was set so as to gradually increase from the same Al mixed crystal ratio as that of the active layer 12 as the distance from the surface of the stripe groove was increased. For example, when manufacturing a semiconductor laser device that emits laser light with a wavelength of about 780 nm,
An Al mixed crystal ratio x gradually increasing to 0.5 was used. However, the Al mixed crystal ratio x only needs to gradually increase from the cleavage plane 23, and is not limited to the range of 0.14 to 0.5. Further, the change in the Al mixed crystal ratio x may be linear or parabolic. Furthermore, the laminated structure 13 including the active layer 12 inside the semiconductor laser device
There may be a step of the Al mixed crystal ratio between the gap band gap layer 16 and the inclined band gap layer 16 with the cleavage plane 23 interposed therebetween. The forbidden belt
The thickness of 16 was about 0.1 μm.

When the organometallic thermal decomposition method is used as in this embodiment, as shown in FIG. 3D, the inclined bandgap layers 16 can be simultaneously formed on both of the cleavage planes 23 facing each other. it can. Here, the organometallic thermal decomposition method was used,
Another vapor phase growth method such as a molecular beam epitaxy method may be used. For example, when the molecular beam epitaxy method is used, while the substrate 11 is being rotated, a molecular beam is irradiated from an oblique direction, so that the entire surface of the cleavage plane 23 has a tilted bandgap layer.
16 can be formed.

On the SiO ₂ film 19, an amorphous film 16 ′ was formed instead of a single crystal film. This amorphous film
16 'is etched much faster than the inclined band gap layer 16 made of a single crystal. Therefore, the substrate 11 was taken out of the vapor phase growth apparatus, and the amorphous film 16 'was selectively removed by a normal etching method. Furthermore, SiO ₂ 19
As shown in FIG. 3 (e),
The substrate 11 having the inclined bandgap layer 16 only on the bottom and side surfaces of the stripe groove including the cleavage plane 23 was obtained. Since the gradient bandgap layer 16 was formed to have a high resistance, no leakage current through this layer was observed.

Next, a resist was buried in the stripe grooves of the substrate 11, and electrodes 14 and 15 were formed on the upper surface of the laminated structure 13 and the lower surface of the substrate 11 excluding this portion. Then, after removing the resist, the substrate 11 was cleaved at a position 24 shown in FIG. Next, using an electron beam evaporation apparatus, a low-reflectance end face reflection film 17 made of Al ₂ O ₃ is formed on the output end face of the resonator, and Al ₂ O ₃ and Al ₂ O ₃ are formed on the other end face of the resonator. A high reflectivity multilayer end face reflection film 18 made of amorphous Si was formed. Finally, each bar was divided into chips to obtain an edge-emitting semiconductor laser device.

The semiconductor laser device obtained in this manner is subjected to a sputtering method using Ar ions to form a gradient band gap layer 16.
When the crystal composition distribution in the thickness direction was measured, no oxygen atoms were detected at the interface between the laminated structure 13 including the active layer 12 and the inclined bandgap layer 16. This is because the cleavage was performed in a sulfur-containing compound solution 26, so that the sulfur atoms were bonded to the cleavage plane 23 to form a protective film.
This is considered to be because oxidation of the cleavage plane 23 by oxygen in the air was suppressed until 11 was introduced into the organometallic thermal decomposition apparatus.

The edge-emitting semiconductor laser device obtained in this example
Even at a high output power of 50 mW, no deterioration in characteristics was observed over a long period of time, indicating extremely high reliability.

Further, in the same manner as in the above embodiment except that a semiconductor layer having a larger forbidden band width than the active layer 12 and having a uniform band gap is formed on the end face of the resonator instead of the inclined band gap layer 16. When the edge-emitting semiconductor laser device was manufactured as described above, high reliability was exhibited in a high output state as in the case of the above embodiment.

In this example, as a solution of the sulfur-containing compound,
A solution of (NH ₄ ) ₂ S, (NH ₄ ) ₂ S _x , or Na ₂ S was used.
This solution may be either a stock solution of these sulfur-containing compounds or an aqueous solution thereof.

(Effect of the Invention) As described above, according to the manufacturing method of the present invention, cleavage can be easily performed by applying ultrasonic vibration.

In addition, when ultrasonic vibrations are applied in the solution of the sulfur-containing compound to cleave the protrusions, ultrasonic vibrations are also applied to the sulfide-containing solution, so that a protective film is formed on the cleavage surface.

Therefore, according to the present invention, since the oxidation of the cleavage plane is reliably prevented by the protective film, the cleavage plane is not oxidized by oxygen in the air.

As a result, according to the present invention, it is possible to achieve an effect that a highly reliable semiconductor laser device without end face deterioration can be realized.

Further, according to the structure further including the step of forming a semiconductor layer having a forbidden band width larger than the forbidden band width of the active layer on the end face of the resonator, the semiconductor layer can be formed on a clean interface.

As a result, a good interface is formed between the stacked structure including the active layer and the semiconductor layer, so that an edge-emitting semiconductor laser device having high reliability even in a high output state can be obtained. Can be played.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of an edge-emitting semiconductor laser device obtained by the manufacturing method of the present invention, and FIG. 2 (a).
FIG. 2B is a perspective view showing a state in which the substrate is immersed in a solution of the sulfur-containing compound put in the beaker. FIG. 2B is a view showing the state in which the beaker shown in FIG. FIGS. 3 (a) to 3 (e) are perspective views showing a step of cleaving by applying ultrasonic vibration to the substrate, FIGS. 3 (a) to 3 (e) are cross-sectional views showing a manufacturing step of the edge-emitting semiconductor laser device of FIG. 1, and FIG. FIG. 5 is a plan view showing the pattern of the SiO ₂ film formed on the surface of the laminated structure on the substrate, FIG. 5 is a perspective view showing the shape of the projection formed on the substrate by using the ion milling method, and FIG. a)
FIG. 6 is a view showing the XX ′ section and the YY ′ section of FIG. 5 together, and FIG. 6 (b) is a view showing the ZZ ′ section of FIG. 11 ... Substrate, 12 ... Active layer, 13 ... Laminated structure, 16 ... Gradient band gap layer, 19 ... SiO ₂ film, 21 ... Protrusion, 22 ... Connecting part,
23 …… Cleavage surface, 26 …… Sulfur-containing compound solution, 27 …… Ultrasonic cleaner

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuaki Sasaki 22-22 Nagaikecho, Abeno-ku, Osaka, Osaka Inside Sharp Corporation (72) Inventor Akihiro Matsumoto 22-22 Nagaikecho, Abeno-ku, Osaka, Osaka Sharp shares In-company (56) References JP-A-59-197184 (JP, A) JP-A-60-231379 (JP, A) JP-A-62-173789 (JP, A) 1990 (Heisei 2) Spring 37 Jpn. 911 Sharp Technical Report 44 “3” 26−30

Claims (2)

(57) [Claims] 1. A method of manufacturing an edge-emitting semiconductor laser device having a laminated structure including an active layer formed on a substrate, comprising: forming a projection on a semiconductor crystal constituting the laminated structure; A step of applying ultrasonic vibration in a solution of a compound to cleave the projection to form a cavity end face and forming a protective film containing sulfur on the cavity end face; Method. 2. The method of manufacturing a semiconductor laser device according to claim 1, further comprising a step of forming a semiconductor layer having a forbidden band width larger than a forbidden band width of said active layer on said cavity facet.