JP2647076B2 - Semiconductor laser device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a semiconductor laser having a current confinement effect and an optical waveguide effect, and particularly to a chemical vapor deposition method using an organic metal (hereinafter referred to as a chemical vapor deposition method). The present invention relates to a semiconductor laser device suitable for manufacturing by the MOCVD method) and a manufacturing method thereof.

(Prior art) In recent years, the MOCVD method has attracted attention as a method for preparing semiconductor materials for semiconductor lasers used as light sources for optical information processing, instead of the conventionally used liquid phase growth method (hereinafter abbreviated as LPE method). I have. This MOCVD method is excellent in uniformity over controllability of composition and film thickness, and is considered to occupy an important position in future laser manufacturing technology.

Unlike the LPE method, the MOCVD method has a drawback that it is difficult to obtain a crystal having good luminous efficiency on a step such as a groove. Therefore, it is necessary to planarize from the substrate to the active layer. As a typical laser structure using the MOCVD method, there is one using GaAlAs as a material as shown in FIG. This is to form a current confinement and an optical waveguide in a self-aligned manner by regrowing GaAlAs on a double hetero wafer having a groove formed therein. In the figure, 51 is an n-GaAs substrate, and 52 is n-GaAs.
-GaAlAs cladding layer, 53 is a GaAs active layer, 54 is p-GaAlAs
Cladding layer, 55 is an n-GaAs current blocking layer, 56 is p-GaAlAs
A clad layer, 57 is a p-GaAs contact layer, and 58 and 59 are electrodes. However, in the laser with this structure, the layer regrown on the groove plays the role of optical confinement and current path, so the demands on the crystal quality of this regrown layer have become strict. Has only been reported.

By the way, as a recent technical trend, as semiconductor materials used for long wavelength lasers for optical communication and short wavelength lasers for optical recording, InGaAsP and InGaAlA, which can have longer and shorter wavelengths, are used.
s, InGaAlP and the like have attracted attention. Among them, the group V element is 1
InGaAlP and InGaAlAs composed only of types are suitable for vapor phase growth. However, these materials are GaAlAs
Difficult to create a complex layer structure due to strict conditions for lattice matching with the substrate crystal, and no trial production of a practical laser with a single fundamental transverse mode has been reported so far. .

The present inventors have developed InGaAlP, InGaA formed by the MOCVD method.
We have been studying semiconductor lasers with a single transverse mode using lAs, but as a result, it is difficult to obtain sufficient characteristics with the device with the structure shown in Fig. 5, which has been conventionally used in lasers using GaAlAs. There was found. That is, in the configuration of FIG. 5, the substrate is GaAs, the cladding layer is InGaAlP, and the active layer is InGaP.
With such a laser, it rapidly deteriorates in an extremely short time of about one hour, and it cannot be expected that the laser will be practically reliable. When the stripe portion of the wafer was examined by X-ray diffraction to investigate the cause of this deterioration, the mismatch of the lattice was 0.1% or less in the portion regrown on the flat surface, while it was found on the groove. A lattice mismatch of 0.2 [%] or more is observed in the regrown portion, and the occurrence of dislocation caused by this large lattice mismatch is considered to be the main cause of rapid deterioration.

Such a phenomenon is considered to be common to mixed crystal materials in which the conditions for lattice matching are strict because the properties of the constituent group V elements are significantly different from those of the substrate. Therefore,
InGaAlP and InGaAlAs expected to increase in demand in the future
In order to realize a semiconductor laser having a single fundamental transverse mode using a semiconductor laser, it is clear that the conventional technique for manufacturing a semiconductor laser using GaAlAs or the like cannot be applied as it is, and a completely new technique is required.

(Problems to be Solved by the Invention) As described above, in the conventional device, when a liquid crystal material such as InGaAlP or InGaAlAs, which has strict conditions for lattice matching, is used, a high-quality crystal is grown on a surface having a step. It is very difficult to realize a semiconductor laser having a single fundamental transverse mode provided with an optical waveguide and a current confinement structure.

The present invention has been made in view of the above circumstances, and its purpose is to provide a high-quality surface with a step even if a liquid crystal material such as InGaAlP or InGaAlAs that has strict conditions for lattice matching is used. And a highly reliable semiconductor laser device having a single fundamental transverse mode.

Another object of the present invention is to provide a method of manufacturing a semiconductor laser device which achieves the above object.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is that a semiconductor laser using a semiconductor material which is difficult to grow due to problems such as lattice mismatch because the constituent group V element is different from the substrate. Forming a heterojunction with a heterogeneous III-V semiconductor composed of the same group V element as that of the substrate around the stripe-shaped protrusion provided in the cladding layer to create an optical waveguide structure with current confinement In this way, it is possible to avoid the regrowth of the semiconductor material in which the crystal growth is difficult, and to switch the group V atmosphere on the crystal surface during the crystal growth in a very short time, thereby forming the semiconductor material composed of mutually different group V elements. This makes it possible to form a heterojunction of a semiconductor to be formed.

That is, the present invention comprises a first conductive type semiconductor substrate, a first conductive type clad layer, an active layer, and a second conductive type clad layer having a stripe-shaped projection, and a double hetero-type clad layer formed on the semiconductor substrate. A semiconductor laser device comprising: a junction structure portion; and a current blocking layer formed on the double hetero junction structure portion by removing at least a part of the projection of the second conductivity type cladding layer, and performing optical waveguide and current confinement. Wherein the constituent materials of the substrate, the double heterojunction structure and the current blocking layer are each formed of a III-V compound semiconductor, and the group V elements of the double heterojunction structure are combined with the constituent V elements of the substrate. And the constituent V element of the current blocking layer is the same as the constituent V element of the substrate.

The present invention also relates to a method of manufacturing a semiconductor laser device having the above structure, wherein a V-group element comprising a first conductivity type cladding layer, an active layer and a second conductivity type cladding layer on a first conductivity type semiconductor substrate. A double heterojunction structure portion containing a group V element different from the above, and a second conductivity type contact layer are successively grown and formed in the above order by a chemical vapor deposition method using an organic metal, and then the second conductivity type contact layer is formed. Forming an etching mask thereon, then selectively etching the contact layer using the mask, and selectively etching the second conductivity type cladding layer halfway to form a stripe-shaped protrusion in the cladding layer; Then, while leaving the mask or after removing the mask, chemical vapor deposition using an organic metal on the double hetero junction structure and on the side surface of the contact layer. It is a method to grow a current blocking layer including the same V group element as the V group element which constitute the substrate by.

(Function) According to the present invention, the current blocking layer grown on the stepped surface is composed of the same group V element as the substrate,
The current blocking layer will be grown in a high quality crystalline state. Therefore, the optical waveguide and the current confinement structure can be formed in a self-aligned manner by using the MOCVD method.
A semiconductor laser using a mixed crystal material having strict conditions for lattice matching, such as InGaAlAs or InGaAlAs, can be realized.

(Example) First, before describing an example, a basic principle of the present invention will be described.

As a technique for forming each layer constituting the semiconductor laser, the present inventors have used a group III methyl organic metal such as trimethyl aluminum, trimethyl gallium and trimetal indium, and a group V hydride arsine and phosphine. An experiment of forming a step on InGaAlAs or InP grown on an InP substrate and regrowing InP or InGaAlAs on this using metalorganic pyrolysis under a pressure lower than atmospheric pressure, and InGaAlP grown on a GaAs substrate Alternatively, an experiment of forming a step on GaAlAs and regrowing GaAlAs or InGaAlP thereon was repeated. As a result, Ga
Regrowth of GaAlAs on AlAs or InGaAlP was easy, but regrowth of high quality InGaAlP was difficult. Moreover, although regrowth of InP on InP or InGaAlAs having a step was easy, regrowth of InGaAlAs was difficult. When these regrown layers were examined by X-ray diffraction,
The lattice constants of InGaAlP and InGaAlAs were significantly different between the step and the flat part, and many transitions were observed.

It is considered that it is difficult to regrow these InGaAlP and InGaAlAs mixed crystals on the step because of the following reasons. That is, In
The lattice constant of InP, GaP, and AlP that constitute GaAlAP is significantly different from the lattice constant of GaAs that this mixed crystal must lattice-match, or the lattice constant is sensitive to composition. This is because, when this mixed crystal is regrown, a difference in the crystal growth between the step portion and the flat portion causes a slight composition shift, which results in a large lattice mismatch. It is also considered that it is difficult to regrow InGaAlAs on the step for the same reason. on the other hand,
In InP, GaAlAs, etc. composed of the same Group V element as the substrate that must be lattice-matched, there is no such problem with lattice matching. Is considered to be able to grow with good reproducibility.

Hereinafter, details of the present invention will be described with reference to the illustrated embodiments.

FIG. 1 is a sectional view showing a schematic structure of a semiconductor laser according to one embodiment of the present invention. In the figure, reference numeral 11 denotes an n-GaAs substrate, on which an n-GaAs buffer layer 12 and n-In
A GaP buffer layer 13 is formed. On the buffer layer 13, an n-InGaAlP cladding layer 14, an InGaP active layer 15, and a p-I
A double heterojunction structure comprising nGaAlP cladding layers 16, 17, 18 is formed. Here, the cladding layer 17 has a low Al composition and acts as an etching stop layer described later. Further, the clad layer 18 is processed in a stripe shape, whereby a stripe-shaped rib is formed in the p-clad layer. On the cladding layer 18, a p-InGaAlP contact layer 1 is formed.
9 and a p-GaAs contact layer 20 are formed. On the side surface of the double hetero junction structure and the contact layer 20, n
A -GaAs current blocking layer 21 is formed. Contact layer 20
On the current blocking layer 21, a p-GaAs contact layer 22 is formed. Then, a metal electrode 23 is attached to the upper surface of the contact layer 22, and a metal electrode 24 is attached to the lower surface of the substrate 11.

In this structure, the current confinement is performed by the contact layer 20 and the current blocking layer 21, and the optical waveguide is performed by the cladding layer 18 formed in a stripe-shaped mesa. The buffer layer
Reference numeral 13 is for improving the quality of the InGaAlP-based crystal formed on GaAs. The contact layer (intermediate contact layer) 19
Is intended to reduce the electric resistance between the cladding layer 18 and the contact layer 20, and may be any as long as the band gap is larger than the contact layer 20 and the band gap is smaller than the cladding layer 18. . Further, the band gap of the intermediate contact layer 19 may be made similar to the band gap at the portion in contact with the cladding layer 18 and the contact layer 20, and may be gradually changed from the cladding layer 18 to the contact layer 20.

Next, a method of manufacturing the semiconductor laser having the above configuration will be described.

2 (a) to 2 (f) are cross-sectional views showing the steps of manufacturing the laser of the embodiment. First, as a raw material, a metal group III organic metal (trimethyl indium, trimethyl gallium, trimethyl aluminum) and a group V hydride (arsine,
MOCV under subatmospheric pressure using phosphine)
According to the D method, n of the plane orientation (100) is determined as shown in FIG.
−0.5 thickness on GaAs substrate 11 (Si-doped, 3 × 10 ¹⁸ cm ⁻³ )
[Μm] n-GaAs first buffer layer 12 (Se-doped, 3 × 10
¹⁸ cm ^-3 ), 0.5 [μm] thick n-InGaP second buffer layer
13 (Se-doped, 3 × 10 ¹⁸ cm ^-3 ), 1.5 μm thick n-I
n _0.5 Ga _0.2 Al _0.3 P first cladding layer 13 (Se-doped, 1 × 10 ¹⁸
cm ^-3 ), 0.1 [μm] thick In _0.5 Ga _0.5 P active layer 15, thickness
0.1 [μm] p-In _0.5 Ga _0.2 Al _0.3 P second cladding layer 16
(Mg doped, 2 × 10 ¹⁸ cm ⁻³ ), p-In _0.5 Ga _0.4 Al _0.1 P third layer having a thickness of 0.02 [μm] acting as an etching stop layer
Cladding layer 17 (Mg doped, 2 × 10 ¹⁸ cm ^-3 ), thickness 1.4 [μ
m] p-In _0.5 Ga _0.2 Al _0.3 P fourth cladding layer 18 (Mg-doped, 2 × 10 ¹⁸ cm ⁻³ ), and a thickness of 0.4 mm as an intermediate contact layer.
01 [μm] p-In _0.5 Ga _0.4 Al _0.1 P first contact layer 1
9 (Mg-doped, 2 × 10 ¹⁸ cm ⁻³ ) and 0.5 μm thick p-
A GaAs second contact layer 20 (Mg doped, 2 × 10 ¹⁸ cm ⁻³ ) was sequentially grown to form a double hetero wafer. Subsequently, an SiO ₂ film 26 was formed on the second contact layer 20 in the form of a stripe having a width of 5 μm and a thickness of 0.1 μm by thermal decomposition of silane gas and photolithography.

Next, as shown in FIG. 2 (b), using the SiO ₂ film 26 as a mask, the second contact layer 20 is etched by a GaAs selective etchant to expose the first contact layer 19, and has a width of 3 [μm]. A GaAs stripe-shaped mesa 27 was formed.

Then, as shown in FIG. 2 (c), the first contact layer 19 and the fourth cladding layer 18 are etched by the selective etching of InGaAlP using the GaAs striped mesa 27 as a mask until the third cladding layer 17 is exposed. Thus, a stripe-shaped mesa 28 was formed.

By processing this wafer with a selective etchant of GaAs, the second contact layer 20 is etched to reduce its width, and a stripe-shaped mesa having the shape shown in FIG.
29 formed. The selective etchant of GaAs is 28%
A mixture of ammonia water, 35% hydrogen peroxide solution and water at a ratio of 1: 30: 9 was used at 20 [° C.]. The selective etching of InGaAlP was performed using sulfuric acid or phosphoric acid at a temperature of 40 to 130 [° C.].

Next, as shown in FIG. 2E, the n-GaAs current blocking layer 21 (Mg-doped, 5 × 10 ¹⁸ cm ⁻³ ) was formed by MOCVD under reduced pressure using trimethylgallium and arsine as raw materials.
Was grown to a thickness of 0.5 [μm]. At this time, the growth is performed after the temperature is raised to 700 ° C. while introducing the diluted phosphine gas.
The phosphine gas flow was switched to the arsine gas flow, and after waiting for about 1 second, the reaction was carried out by introducing a trimethylgallium organometallic gas. As a result, Ga on the SiO ₂ film 26
As growth was not observed at all, and a wafer having a sectional shape shown in FIG. 2 (e) was obtained.

Next, after removing the SiO ₂ film 26, as shown in FIG. 2 (f), the p-GaAs third contact layer 2 is entirely formed by MOCVD.
2 (Mg-doped, 5 × 10 ¹⁸ cm ⁻³ ) was grown to a thickness of 3 μm. Thereafter, an Au / Zn electrode 23 is applied on the third contact layer 22 and an Au / Ge electrode 24 is applied on the lower surface of the substrate 11 by a normal electrode attaching process, so that the laser wafer having the structure shown in FIG. I got

The thus obtained wafer is cleaved to have a cavity length of 250.
When a [μm] laser device was fabricated, the threshold current
Good characteristics of 90 [mA] and differential quantum efficiency of 20 [%] per side were obtained. The light output increased linearly to 20 [mW] or more according to the drive current, and showed good current-light output characteristics without kink. Further, it was found that both the far-field image and the near-field image were unimodal, and that good mode control was performed.

As described above, according to the present embodiment, the current confinement structure and the optical waveguide structure can be formed in a self-aligned manner, and GaAs is used as the current blocking layer 21. Layer 21 can be grown in a high quality crystalline state. Therefore, even when InGaAlP, which has strong demands, is used as a light source for optical information processing, it has a single fundamental transverse mode and small astigmatism, and has stable operation even under the feedback of a large amount of external reflected light. Semiconductor lasers can be realized with good reproducibility and high reliability.
Its usefulness is enormous. Further, since the electrode 23 is provided on the flat surface of the third contact layer 22, the contact resistance between the contact layer 22 and the electrode 23 can be sufficiently reduced, and the electrode 23 may be deformed. Absent. For this reason, there are also advantages such as improvement in element characteristics and reliability.

Further, according to the manufacturing method of the present embodiment, various difficulties which are usually problems are skillfully avoided. That is, formation of an optical waveguide by selective etching and creation of a current confinement structure by MOCVD under reduced pressure provide good reproducibility without using advanced fine processing technology. In addition, as in the embodiment, In
When GaAlP and GaAs (which may be GaAlAs) are combined to form an optical waveguide and current confinement structure, InGaAlP and G
It is necessary to regrow on the surface where aAs is exposed at the same time. However, it is usually difficult to suppress damage to the crystal surface due to evaporation of P and As at the time of raising the temperature simultaneously with both InGaAlP and GaAs. However, in the growth method adopted here, since the GaAs surface is covered with the SiO ₂ layer 26, the above problem does not occur, and good growth is achieved by raising the temperature in a P atmosphere. Is done. Further, in this embodiment, the width of the stripe-shaped SiO ₂ film 26 is 5 [μm].
The width of the top of the second contact layer 20 is reduced to 3 [μm]. Therefore, the shape of the GaAs current blocking layer 21 after growth is as shown in FIG. 2 (f), and the periphery of the second contact layer 20 forming the current flow path is flat. There is an advantage that the electrode formation is easy.

The present invention is not limited to the embodiments described above. For example, the third contact layer 22 is omitted, and the third
As shown in the figure, the electrode 23 may be directly deposited on the second contact layer 20. Instead of forming the third contact layer 22, the P-type diffusion layer 41 may be formed by diffusion or ion implantation of a P-type dopant such as Zn as shown in FIG. Here, in the example of FIG. 4, the SiO ₂ film 26 is removed during the growth of the current blocking layer 21 in FIG. The diffusion layer 41 is formed in a portion to be formed.

In the embodiment, the p-InGaAlP fourth cladding layer is etched to form the striped ribs, and then the p-GaAs second contact layer is re-etched. However, this re-etching step is not always necessary. Also, p-InGaAlP
May be formed as a single layer. Furthermore, the p-InGaAlP first contact layer (intermediate contact layer) does not necessarily have to be used.

Further, the present invention can be similarly applied to lasers using materials other than those described in the embodiments. For example, GaAs
GaAlAs, InGaAsP or InP substrate
A laser using nGaAlAs or InGaAsP can be considered. Further, in the embodiment, the first conductivity type is n-type and the second conductivity type is p-type. However, it is needless to say that these may be reversed. In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described above in detail, according to the present invention, a current blocking layer grown on a surface having a step like a stripe-shaped convex portion of a second conductivity type cladding layer is made of the same group V element as a substrate. , The current blocking layer can be grown in a high-quality crystalline state while the current confinement structure and the optical waveguide structure are formed in a self-aligned manner. For this reason, InGaAlP and InGaAlA
Despite the use of a mixed crystal material with strict conditions for lattice matching such as s, a highly reliable semiconductor laser having a single fundamental transverse mode will be realized, and a light source for optical information processing It is extremely effective.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an element structure of a semiconductor laser according to one embodiment of the present invention, and FIGS. 2 (a) to 2 (f) are cross-sectional views showing manufacturing steps of the laser of the above-described embodiment, and FIGS. 4 is a sectional view showing a modification, and FIG. 5 is a sectional view showing an element structure of a conventional laser. 11 ... n-GaAs substrate, 12 ... n-GaAs buffer layer, 13 ...
... n-InGaP buffer layer, 14 ... n-InGaAlP cladding layer (first conductivity type cladding layer), 15 ... InGaP active layer, 16, 1
7,18 ... p-InGaAlP cladding layer (second conductivity type cladding layer), 19 ... p-InGaAlP contact layer, 20,22 ... p-
GaAs contact layer, 21 ... n-GaAs current blocking layer, 23, 24
…… electrode, 26 …… SiO ₂ film.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masayuki Ishikawa 1st Toshiba-cho, Komukai-shi, Kawasaki-shi Inside Toshiba Research Institute, Inc. Within the Research Institute (56) References JP-A-62-166586 (JP, A)

Claims (7)

(57) [Claims] 1. A double hetero-type GaAs substrate comprising a first conductivity type GaAs substrate, a first conductivity type cladding layer, an active layer and a second conductivity type cladding layer having a stripe-shaped projection. A junction structure, a first conductivity type current blocking layer formed on the double hetero junction structure by removing at least a part of the projection of the second conductivity type cladding layer, and a projection of the second conductivity type cladding layer; A semiconductor laser device having at least two or more second conductivity type contact layers formed on the portion and performing optical waveguide and current confinement, wherein the constituent materials of the double hetero junction structure portion and the current blocking layer are II, respectively.
An IV group compound semiconductor, wherein the double heterojunction structure portion includes a group V element different from the As element constituting the substrate, the current blocking layer includes the same As element as the substrate, The semiconductor laser device according to claim 1, wherein the blocking layer protrudes at a portion corresponding to a shoulder of the projection of the second conductivity type cladding layer, and is higher than the two layers of the second conductivity type contact layer. 2. The method according to claim 1, wherein the double hetero junction structure is In _x Ga _1-xy.
Al _y P (0 ≦ y ≦ 1) The current blocking layer is Ga _{1 -z} Al _z As (0 ≦
2. The semiconductor laser device according to claim 1, wherein z ≦ 1). 3. The semiconductor laser device according to claim 1, wherein said second conductivity type contact layer on said second conductivity type cladding layer is three layers. 4. A contact layer of the second conductivity type immediately above the cladding layer of the second conductivity type has a larger band gap than the contact layer on the contact layer and a smaller band gap than the cladding layer. The semiconductor laser device according to claim 1, wherein: 5. The intermediate contact layer has a smaller band gap nearer to the contact layer, a larger band gap nearer to the second conductivity type cladding layer, and the band gap gradually changes therebetween. 5. The semiconductor laser device according to claim 4, wherein 6. A method for manufacturing a semiconductor laser device comprising a III-V compound semiconductor material, comprising a first conductivity type cladding layer, an active layer and a second conductivity type cladding layer on a first conductivity type GaAs substrate. V different from As element constituting the substrate
A step of successively growing and forming a double heterojunction structure containing a group III element and a second conductivity type contact layer in the above order by a chemical vapor deposition method using an organic metal; Forming an etching mask;
Then, the contact layer is selectively etched using the mask, and the second conductivity type cladding layer is selectively etched halfway to form stripe-shaped protrusions in the cladding layer, and then the mask is left. As it is or after removing the mask, at least on the double hetero junction structure and on the side surfaces of the contact layer, a current blocking layer containing the same group V element as the As element constituting the substrate by a chemical vapor deposition method using an organic metal. Growing the semiconductor laser device so as to protrude at a portion corresponding to a shoulder of the convex portion of the cladding layer. 7. The method according to claim 1, wherein the mask is left when forming the current blocking layer, the mask is removed after forming the current blocking layer, and then an organic metal is used on the contact layer and the current blocking layer. 7. The method for manufacturing a semiconductor laser device according to claim 6, wherein the second conductivity type contact layer is formed again by chemical vapor deposition.