JP2828235B2 - Semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge emitting type high power semiconductor laser device of the AlGaAs type.

[0002]

2. Description of the Related Art Al is used as a light source for an optical disk device or the like.
GaAs-based semiconductor laser devices have been widely used. When a semiconductor laser device is used as a light source of a writable write-once optical disc device, it is required to have high reliability even in a high light output state of 50 mW or more. When used as an excitation light source for a YAG (Yttrium Aluminum Garnet) laser device or a light source for a high-definition printer, a high output of 100 mW or more is required.

[0003] As a practical way to achieve higher output of the semiconductor laser device, such as reflectivity to the light emitting end surface is 10%, the low reflectance protective film, for example made of Al ₂ 0 _3, the light emitting side The end face on the opposite side has a reflectance of 90%.
For example, there is a method of increasing the external quantum efficiency by forming a high reflectance protective film composed of a multilayer film of an Al ₂ O ₃ layer and a Si layer. High output characteristics of 100 mW or more have been confirmed in a 780 nm band semiconductor laser device controlled in the transverse mode by this method.

[0004]

However, in a semiconductor laser device in which a low-reflectance protective film and a high-reflectance protective film are simply formed on an end face, there is a problem in reliability of high-output characteristics for a long period of time. The main cause is end face deterioration. This is because the light emission end face has a high light density and generates heat locally. This heat is generated when electrons or holes as carriers are trapped in the surface states existing on the light emitting end face, and energy is released through a non-light emitting process. In particular, when the laser is oscillated at a high output, the calorific value increases and the temperature of the light emitting end surface rises, eventually reaching the melting point of the crystal, and the end surface is destroyed (CO 2).
D) occurs.

A method of forming a film containing S (sulfur) on the light emitting end face has been proposed in order to prevent such end face deterioration due to heat generation at the light emitting end face (for example, Extend).
edAbstracts of the 21st Conference on Solid State
Devices and Materials, Tokyo, (1989) p337-340). According to this method, the maximum light output of the semiconductor laser device is improved to 200 mW or more, which is twice the normal value. This is because the S atomic layer or the S molecular layer terminates dangling bonds existing on the light emitting end face of the semiconductor laser and inactivates the light emitting end face. In other words, the above surface state density, which has hindered the improvement of the light emission characteristics of the semiconductor laser, can be significantly reduced.

However, even with the proposed method of forming the S-containing film on the light emitting end face, a problem remains in the long-term reliability of the semiconductor laser device. This is because the bond between the dangling bond on the light emitting end face and S is weak, and O (oxygen) which causes a surface level instead of S as a result of driving in a high output state for a long period of time is not connected to the light emitting end face. This is because an oxide film is formed in association with a bond.

[0007] By the way, GaAs is targeted, but in order to improve the surface condition, G is applied to the surface of GaAs.
A method of forming a few atomic layer of an InP layer having a larger lattice constant than aAs is known (Extended Abstracts of the 23r).
d Conference on Solid State Devices and Materials,
Yokohama (1991) pp.683-685). This is GaAs
Remove the oxide film that causes the formation of surface levels on the surface of
A kind of window layer is formed on the GaAs surface. The InP layer serves as the window layer because the InP layer serves as the G layer of the laser element.
This is because the band gap of the InP layer is significantly increased due to the strain caused by receiving compressive stress from aAs.

However, the end face of the optical element, in particular, Al
As for the end face of the GaAs-based semiconductor laser device, no improvement has been attempted so far by forming an ultra-thin film on the surface as described above. This is because Al is a very active substance, and its oxide film is stable, and it has been considered that the above method cannot form a good AlGaAs surface having a small surface level.

An object of the present invention is to provide an AlGaAs-based semiconductor laser device which can suppress a surface level caused by an oxide on a light emitting end face and hardly cause end face destruction even in a high output state.

[0010]

According to a semiconductor laser device of the present invention, one layer of a laser element having a plurality of stacked layers is A
In a semiconductor laser device comprising an lGaAs active layer,
InP or In _x Ga _1-x P is formed on the light emitting end face of the laser element.
(X> 0.5).
Thus, the above object is achieved.

The semiconductor laser device of the present invention has a plurality of
A compound semiconductor laser device comprising a stack of layers, wherein A
An active layer made of lGaAs and a light emitting end face
Material containing InP or InGaP as a main component,
Is a light emitting end face protective film made of InP or InGaP.
Formed between the light emitting end face protective film and the light emitting end face.
AlGaAs having an Al mixed crystal ratio larger than that of the active layer.
s window layer to achieve the above object
Is done.

The light emitting end face protective film is made of In _x Ga.
It is formed of a material containing _1- xP and has an In composition ratio of 0.49.
It may be larger than that .

The thickness of the layer formed on the light emitting end face is:
The thickness of the layer may be smaller than the critical layer thickness at which dislocation occurs.

[0014]

According to the semiconductor laser device of the present invention, a layer made of a material containing InP or InGaP is formed on the light emitting end face. Although a slight surface level is also formed on the surface of the layer formed on the light emitting end face, the lattice constant of the layer formed on the light emitting end face is larger than that of the AlGaAs active layer. Alternatively, the band gap of the InGaP intermediate layer becomes extremely large. Therefore, the carriers trapped in the surface level are re-injected into the conduction band or valence band of the AlGaAs active layer by a tunneling (resonance) effect and used for light emission, and do not generate heat on the surface. That is, the layer formed on the light emitting end face acts as a kind of window layer.

It is more effective when a window layer made of AlGaAs having an Al mixed crystal ratio higher than that of the AlGaAs active layer is formed between the light emitting end face and the layer formed on the light emitting end face. .

In order to make the lattice constant of the layer formed on the light emitting end face larger than that of the AlGaAs active layer, there is no problem when the layer formed on the light emitting end face is formed of a material containing InP. In the case where the InGaP is formed of a material containing In, the composition ratio of In in InGaP may be set to be greater than 49% with respect to the whole of the group III elements In and Ga.

The layer formed on the light emitting end face is A
Although it is a lattice mismatching system with respect to the lGaAs system, if it is formed thinner than the critical layer thickness at which dislocations occur, it is possible to prevent the crystallinity from being affected.

[0018]

Embodiments of the present invention will be described below.

AlGaAs as a matrix to which the present invention is applied
The basic structure of the s-based semiconductor laser device may be any known end-face emission type device conventionally used, but here, a VSIS (V-channeled substrate) is used.
inner stripe) laser (eg Applied Physics Le
tters vol.40 (1982) 372).

<< First Embodiment >> FIG. 1 is a perspective view showing the vicinity of an end face of a semiconductor laser device according to a first embodiment. The VSIS laser as a base to which the present invention is applied is p-Ga
An n-GaAs current confinement layer 21 and a p-Al
_0.45 Ga _0.55 As clad layer 12, p-Al _{0. 15} Ga
_{A 0.85} As active layer 13, an n-Al _0.45 Ga _0.55 As clad layer 14, and an n-GaAs cap layer 15 are laminated in this order, and electrodes 31 and 32 are further formed on the upper and lower sides thereof. The n-GaAs current confinement layer 21 has a V-shaped groove for forming a current path and an optical waveguide. This laser device is of the 780 nm band,
It is manufactured by LPE (Liquid Phase Epitaxy) growth.

A layer 51 made of InP is formed at a thickness of 15 Å on the light emitting end face of the laser element,
A low reflection protective film 61 made of Al ₂ O ₃ is formed thereon. Hereinafter, the layer 51 is referred to as an intermediate layer. A high-reflection protective film is formed on the end face opposite to the light exit side. Middle layer 5
Reference numeral 1 denotes a method in which a light emitting end face of a semiconductor laser device is formed by cleavage and then MOCVD (Metal Organic Chemic) is performed using TMI (trimethyl indium) and PH ₃ (phosphine).
al Vapor Deposition) method. Also, the protective film 61
Was prepared by an electron beam evaporation method.

FIG. 2 shows the current vs. light output characteristics of the above-mentioned semiconductor laser device by a curve A. For comparison, the characteristics of a semiconductor laser device having the same configuration as the conventional one in which a protective film is directly formed on the end face after cleavage is shown. Is shown by curve B. As can be understood from this figure, in the conventional example, the laser element is deteriorated due to the end face destruction at an optical output of about 120 mW, whereas in the present embodiment, the optical output of a maximum of about 250 mW is obtained.
Moreover, no end face breakage has occurred at that time.

As described above, a test was conducted to elucidate the reason why the present embodiment could obtain a high light output. Al _0.15 Ga _0.85
A sample in which an As single layer was grown on a GaAs substrate,
Another sample in which an InP layer was formed on the surface of the same sample by 15 angstrom was prepared and evaluated by the photoluminescence method. As a result, the latter obtained a strength 50 times larger than the former. From this, it is understood that in this embodiment, the surface level caused by the oxide film was reduced.

Al _0.15 Ga _0.85 A on which an InP layer is formed
The effect of improving the surface of the s active layer can be explained as follows using the energy phase diagram near the end face shown in FIG.
FIGS. 3A and 3B are state diagrams respectively showing a case where an InP layer is formed and a case where an InP layer is not formed. If you do not form an InP layer, Al _0.15 Ga _0.85 As is will be able many levels on the surface because it contains Al, capture overflow the AlGaAs active layer to the level as shown in FIG. 3 (b) The generated carriers are non-radiatively recombined to generate heat. on the other hand,
When an InP layer is formed, as shown in FIG.
The surface of the active layer of _0.15 Ga _0.85 As becomes an interface with the InP layer, and a strong bond between Al _0.15 Ga _0.85 As and InP is formed, so that a surface level hardly occurs. At this time, In
When the P layer receives a compressive stress, the band gap energy is significantly increased, and the P layer is in a state as illustrated. In this case, although the surface level slightly remains on the surface of the InP layer,
Since the P layer does not contain Al, the density of surface levels is extremely low. Even if carriers are trapped in this level, the carriers are tunneled into the Al _0.15 Ga _0.85 As semiconductor layer due to the thin InP layer. ) Is re-injected by the effect and used in the light emission process and does not contribute to heat generation Therefore, a kind of window effect is generated, and the output characteristics are improved.

By the way, the same evaluation was performed on a semiconductor laser device using GaAs as an active layer. As a result, the improvement in photoluminescence intensity by forming an InP layer was about 10 times, and the semiconductor laser device of the present invention using AlGaAs as an active layer was used. It was found that the degree of improvement of the surface condition was larger in the case of the apparatus. Therefore, it is presumed that the above-mentioned large improvement effect of the surface state of the AlGaAs semiconductor layer is caused by the presence of Al, contrary to what has been conventionally considered.

As described above, the effect of reducing the surface level of the AlGaAs active layer is, as described above, by terminating the dangling bonds on the surface with the S atomic film or the molecular film and inactivating them. But you can. In fact, an optical output of about 220 mW has been observed even in a 780 nm band VSIS laser whose surface is covered with an S film (Extended Abstractsoft).
he 21st Conference on Solid State Devices and Mate
rials, Tokyo, (1989) p337-340). However, In
When a P layer is used, the bond between AlGaAs and S
Since the bonding is much stronger than the bonding with GaAs, the surface state can be kept good for a long time. To prove this, a 780 nm band VS with an InP layer formed on the surface
IS laser and the same laser on which the S film is formed
After driving for 500 hours under the condition of 0 mW, the maximum light output was measured. In the former semiconductor laser device, light output was observed up to 250 mW as before the long-time driving, but in the latter semiconductor laser device, only 130 mW, which is about the ordinary semiconductor laser device, was observed. That is, it was proved that the present invention for forming the InP layer had much higher durability.

<< Second Embodiment >> A second embodiment of the present invention comprises:
The intermediate layer 51 made of InP shown in FIG. 1 and showing the first embodiment is an intermediate layer made of In _0.9 Ga _0.1 P having a thickness of 20 Å. Also in the case of this intermediate layer, AlG
The lattice constant is larger than that of the aAs system,
When the semiconductor layer made of GaAs receives a compressive stress, the band gap energy increases. Also in the semiconductor laser device having this structure, an optical output of a maximum of 260 mW was obtained for the same reason as in the first embodiment, and an effect twice as large as that of the ordinary example was confirmed.

Third Embodiment FIG. 4 shows a third embodiment of the present invention. In the semiconductor laser device of this embodiment, after growing an AlGaAs-based VSIS laser as a base material, an end face is formed by a cleavage method or etching, and a light emitting end face is formed on the end face.
OCVD method in a thickness 0.2μm of Al _0.5 Ga _{0 .5} As window layer 52, an intermediate layer 51 made of a thickness of 10 Å InP successively grown further by sputtering to form a protective film 61 is formed thereon Produced.

The present semiconductor laser device and an Al _0.5 G
When a semiconductor laser device in which only the a _0.5 As window layer 52 and the protective film 61 are formed and the intermediate layer 51 is not formed is compared, the latter has a maximum optical output of 340 mW.
In the former, an optical output of 500 mW at the maximum was obtained, and the output characteristics were also greatly improved.

The reason for the above improvement can be explained as follows using the energy phase diagram as before. FIG.
(A) shows the energy state near the surface in the semiconductor laser device of the present embodiment, and (b) shows the semiconductor laser device in which the intermediate layer is omitted. In the case of the semiconductor laser device in which the intermediate layer is omitted, as shown in FIG. 5B, the Al _0.5 Ga _0.5 As window layer 52 prevents light absorption near the end face and diffusion of carriers, but flows on the surface. small leakage current 101 Al _{0. 5} G
It is trapped by the surface levels formed on the surface of the a _0.5 As window layer 52 and leads to a small amount of heat generation through a non-light emitting process. On the other hand, in the case of the present embodiment, the surface level of the Al _0.5 Ga _0.5 As window layer 52 disappears due to the presence of the intermediate layer 51, and a slight surface level is formed on the surface of the intermediate layer 51 instead. Only. Carriers caused by a small leak current trapped at this level are tunneled (resonant).
Since it is re-injected into the AlGaAs active layer of the laser element by the effect and used for light emission, it does not lead to heat generation. Therefore, the effect of increasing the maximum light output as described above can be obtained.

The semiconductor laser device according to the present embodiment has excellent characteristics in terms of long-term reliability. That is, the semiconductor laser device in which the intermediate layer is not formed and only the Al _0.5 Ga _0.5 As window layer is formed is 60. 1000 ° C under driving conditions of 70 mW
After a lapse of time, the failure rate of 1% was shown, whereas the failure rate of the semiconductor laser device of this embodiment was 0.1% under the same conditions.
Met.

In the first, second, and third embodiments,
The intermediate layer formed on the light emitting end face of the AlGaAs laser device was formed of InP or In _0.9 Ga _0.1 P. However, the material of the intermediate layer has a lattice constant larger than that of the AlGaAs active layer, that is, receives a compressive stress. Any material can be used as long as the material has a band gap energy larger than that of the AlGaAs active layer. Specifically, when the material is In _x Ga _1-x P, x>
It may be 0.49. The intermediate layer is made of InP or InG
It may contain aP as a main component and some other elements. In the above example, the thickness of the intermediate layer was as very small as 10 to 20 angstroms, but may be any thickness as long as no dislocations are generated in the crystal of the intermediate layer due to strain and no surface states are formed. . The applied laser element is VSI
The structure is not limited to the S laser, and may have any structure.

[0033]

As is apparent from the above description, since the semiconductor laser device of the present invention has an intermediate layer made of a material containing InP or InGaP on its light emitting end face, it does not lead to heat generation, The output end face is less likely to be broken, and the maximum light output can be improved. When a window layer is further provided, the effect can be further increased. In the case of the intermediate layer made of InGaP, when the composition ratio of In is set to be greater than 49% of the total of In and Ga, the lattice constant of the intermediate layer can be made larger than that of the semiconductor layer made of AlGaAs. Although the intermediate layer is a lattice-mismatched system with respect to the AlGaAs system, when the intermediate layer is formed thinner than the critical layer thickness at which dislocations occur, the crystallinity can be prevented from being adversely affected.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the vicinity of an end face in a semiconductor laser device according to a first embodiment.

FIG. 2 is a diagram illustrating a relationship between a current and an optical output in the semiconductor laser device according to the first embodiment, together with a relationship in a conventional example.

FIG. 3A is an energy state diagram near an emission end face of the semiconductor laser device of the first embodiment, and FIG. 3B is an energy state diagram near an emission end surface of a conventional semiconductor laser device.

FIG. 4 is a perspective view showing the vicinity of an end face in a semiconductor laser device according to a third embodiment.

FIG. 5A is an energy state diagram near an emission end face of a semiconductor laser device according to a third embodiment, and FIG. 5B is an energy state diagram near an emission end surface of a conventional semiconductor laser device.

[Explanation of symbols]

 Reference Signs List 11 p-GaAs substrate 12 p-AlGaAs cladding layer 13 p-AlGaAs active layer 14 n-AlGaAs cladding layer 15 n-GaAs cap layer 21 n-GaAs current confinement layer 31, 32 electrode 51 layer made of InP or InGaP 52 AlGaAs window Layer 61 Protective film 101 Micro leakage current flowing on the surface

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tadashi Takeoka 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Masanori Watanabe 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (72) Inventor Osamu Yamamoto 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Hiroshi Nakatsu 22-22 Nagaike-cho, Abeno-ku, Osaka-shi Osaka Prefecture Inside Sharp Corporation (56) JP-A-4-315487 (JP, A) JP-A-2-213185 (JP, A) 1991 (Heisei Era) 52nd Autumn Meeting of the Japan Society of Applied Chemistry 9a-ZM-8 p. 971 (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/18

Claims (2)

(57) [Claims] 1. A laser device comprising a plurality of stacked layers.
Semiconductor laser device whose layer consists of an AlGaAs active layer
Oite, InP on the light emitting facet of the laser device or In _x Ga _1-x P
A semiconductor laser device in which a layer made of a material containing (x> 0.5) is formed . 2. A compound semiconductor laser comprising a plurality of stacked layers.
An active layer made of AlGaAs and an InP or InGaP formed near the light emitting end face.
Is InP or InGaP?
A light-emitting end face protective film made of, and formed between the light-emitting end face protective film and the light-emitting end face;
AlGaAs window layer having a mixed crystal ratio greater than that of the active layer
The semiconductor laser device provided with and.