JPH0766992B2 - AlGaInP semiconductor laser and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a semiconductor laser, particularly an AlGaInP-based semiconductor laser, and a method for manufacturing the same.

[Conventional technology]

Regarding semiconductor lasers, various structures have been proposed in order to improve various characteristics such as the current threshold, oscillation characteristics, and radiation angle, or obtain characteristics suitable for the purpose of use.

In such a semiconductor laser, in order to concentrate current in the lateral direction or to substantially confine carriers or light, in order to form an internal stripe structure or to form a difference in refractive index, groove processing, that is, unevenness is formed. Is often formed, and a manufacturing procedure for forming a semiconductor layer thereon is often taken.

For example, in the structure shown in FIG.
Type GaAs single crystal substrate (1) in the cavity length direction, for example, the fourth
In the figure, a stripe-shaped groove (2) extending in a direction orthogonal to the paper surface is formed by, for example, etching, and a first clad layer (3) made of n-type AlGaAs is sequentially formed on the substrate (1) in which the groove is formed. -GaAs active layer (4) -p-type AlGa
Second cladding layer made of As (5) -p-type low resistance Ga
An As cap layer (6) is formed, a bent portion is formed in the active layer (4) in the lateral direction, and light is also confined in the lateral direction by the first and second cladding layers (3) and (5). It was done like this. (7) is an insulating layer deposited and formed on the cap layer (6), and one electrode (8) is ohmicly deposited on the cap layer (6) through an electrode window formed in the insulating layer. Further, (9) shows the other electrode ohmicly deposited on the substrate (1).

On the other hand, recently, in the production of various compound semiconductors such as AlGaAs or AlGaInP, so-called MOCVD (Metalorga)
nic Chemical Vapor Deposition) or MBE (Molecula
Application of organic metal or metal vapor phase epitaxy such as r Beam Epitaxy is desired. This is because when a semiconductor layer is epitaxially grown by MOCVD or MBE, it is easy to obtain a semiconductor layer having excellent crystallinity, and the composition of the semiconductor layer is controllable.
This is due to the advantage of excellent controllability of thickness, controllability of impurity concentration, and the like.

Actually, in an AlGaAs semiconductor laser having a wavelength band of 0.8 μm, for example, by an organic metal or metal vapor phase epitaxy method on a surface to be epitaxially grooved as in the structure of FIG. 4 described above. The epitaxy of the semiconductor layer is good.

On the other hand, in magneto-optical discs and the like, development of a semiconductor laser that emits light with a short wavelength is desired due to the demand for high-density recording, and for example, practical use of an AlGaInP-based semiconductor laser that emits light of 580 to 650 nm is required.

[Problems to be solved by the invention]

Even when manufacturing the AlGaInP-based semiconductor laser that emits short-wavelength light as described above, it is desirable to use the MOCVD or MBE organic metal or metal vapor phase epitaxy method with excellent controllability for each point as described above.
In the case of subjecting a compound semiconductor of the system to MOCVD or MBE, the condition for achieving good epitaxy depends on the crystal plane of the epitaxy plane, that is, whether it is a (100) crystal plane or a (111) crystal plane, for example. different.

Therefore, for example, in the structure described in FIG.
When the main surface of the substrate (1) is a (100) crystal plane, even if the bottom surface of the groove (2) is (100), another inner surface of the groove (2) is different from the (100) crystal surface. Crystal plane, eg (111)
Since it is a crystal plane, the conditions for epitaxy by MOCVD or MBE on both sides are different, which makes it difficult to satisfactorily form an AlGaInP-based semiconductor layer on this groove (2) by MOCVD or MBE. (11
1) Crystal growth by MOCVD or MBE on the crystal plane is extremely difficult. Generally, the light emitting end face of a semiconductor laser,
That is, since the resonator end face is formed by the cleavage plane (110) crystal face of the crystal, when the substrate (1) having the (100) crystal face is used, the groove (2) in the cavity length direction is formed.
The formation direction of will be selected in the (110) axis direction,
The inner surface of the groove (2) is a surface other than the (100) crystal plane. When the groove (2) is formed by, for example, chemical etching having crystal anisotropy, the inner side surface of the groove (2) is the (111) A surface, and the (111) A surface is Since it is difficult to grow crystals by MOCVD or MBE, there is a problem that it is extremely difficult to perform high-quality epitaxial growth, that is, to form a semiconductor layer having good crystallinity.

The present invention aims to avoid such problems as AlGa
An InP semiconductor laser and a method for manufacturing the same are provided.

[Means for solving problems]

The semiconductor laser according to the present invention has at least a first cladding layer (23), a flat active layer (24), and a second active layer (24), as shown in a schematic sectional view of an example thereof in FIG. In an AlGaInP-based semiconductor laser having a clad layer (25), a concavo-convex having a current confinement function and a side surface having a (111) crystal plane is provided on the second clad layer (25), and AlGaAs is formed on the concavo-convex. Alternatively, a GaAs-based semiconductor layer is formed.

The method of manufacturing an AlGaInP-based semiconductor laser according to the present invention includes a step of forming a flat AlGaInP semiconductor layer for forming a first clad layer, an active layer, and a second clad layer by an organic metal or metal vapor phase epitaxy method. A step of forming a semiconductor layer on the second clad layer and subjecting at least this semiconductor layer to a concavo-convex process having a (111) crystal plane on its side surface to form a functional portion for current constriction; A process for forming an AlGaAs or GaAs-based semiconductor layer by metal or metal vapor phase epitaxy
System semiconductor laser.

[Action]

According to the present invention, the AlGa
A light emitting mechanism portion formed of an InP-based semiconductor layer, for example, a tabular heterojunction portion, is formed by MOCVD or MBE in particular, followed by concavo-convex processing, each portion formed thereafter, that is, a light emitting mechanism, in other words, a light emission wavelength. As for the semiconductor layers that compose the part other than the part that determines, since it is composed of AlGaAs or GaAs-based semiconductor layers, which have small dependence of the epitaxy condition on the crystal plane of the epitaxial surface, AlGaInP-based short wavelengths with excellent characteristics A semiconductor laser that emits light can be obtained.

〔Example〕

An example of the present invention will be described with reference to FIGS.
In this example, an AlGaInP-based semiconductor laser is obtained in which the light emitting mechanism section adopts a table-heterojunction type structure and a gain guide type structure is formed in which the current is concentrated in the center. In this case, as shown in FIG. 1, a substrate of one conductivity type, for example, an n-type GaCs single crystal substrate (21) is provided. This board (21)
Has a (100) crystal plane in its plate surface direction, that is, a main surface. MOCVD is performed on one main surface of this substrate (21).
Buffer layer (22) is epitaxially grown by the method as required, and then a first clad layer (23), an active layer (24), which constitutes a table-heterojunction type light emitting mechanism, is formed on the buffer layer (22),
The second cladding layer (25) is sequentially and sequentially epitaxially grown by MOCVD. Furthermore, subsequently, if necessary, a protective semiconductor layer (26) for the second cladding layer (25) is epitaxially formed thereon, and a current constriction layer (27) is formed thereon.
Epitaxy. These layers (22)-(27) are
It can be formed continuously in a MOCVD operation.

The buffer layer (22), the first cladding layer (23), and the current confinement layer (27) are made of, for example, n-type having the same conductivity type as the substrate (21), and the second cladding layer (25) and its protective semiconductor. The layer (26) has another conductivity type, for example, p-type. The buffer layer (22) is formed of, for example, a GaAs semiconductor layer, and the first and second cladding layers (23) and (25) are n-type and p-type (Al _x Ga _1-x ) _z In _{1 respectively. -2} P, the active layer (24) is (Al _y Ga _1-y ) _z In _1-z P, which is higher than that of the first and second cladding layers (23) and (25). , Al is not added to the active layer (24) or the amount of Al is made smaller than that of the cladding layers (23) and (25) so that the energy band gap Eg becomes small. The active layer (2) is preferably formed by these confinement layers (23) and (25).
XY> 0.3 is selected so that carrier and light can be confined in 3). In the above composition, the value of z from the top of the lattice matching is actually desired to be about z = 0.52 ± 0.01, and at z = 0.52, when y = 0, that is, when Ga _0.52 In _0.48 P, Eg is 1.9 eV. And when x = z, that is, when Al _0.52 In _0.48 P, Eg = 2.3
It will be 5 eV.

The protective semiconductor layer (26) may be formed of a GalnP layer containing no Al, and the current confinement layer (27) may be formed of a GaAs layer.

Then, as shown in FIG. 2, the current confinement layer (27) is selectively etched using, for example, an etching solution of a mixed solution of H ₃ PO ₄ , H ₂ O _2, and H ₂ O, such as photoetching. By doing so, a striped portion (27a) of the current constriction layer (27) is formed. In this case, G of the protective semiconductor layer (26)
alnP. When exposed by selective etching of the current confinement layer (27) by GaAs, the etching rate thereof decreases by an order of magnitude, so that the removal portion (27a) can be reliably formed by stopping the etching at this point. In this case, the presence of the protective semiconductor layer (26) prevents the second cladding layer (25) containing Al, which is relatively easily oxidized, from being directly exposed to the outside through the removal portion (27a). The cladding layer (25) of the
It is possible to avoid the inconvenience that the formation of a) causes oxidation and deterioration of characteristics.

After the removal portion (27a) is thus formed, as shown in FIG. 3, the protection semiconductor layer (2) is formed through the removal portion (27a).
6), the current confinement layer (27) is buried, and a second cladding layer (25) and a protective semiconductor layer (26) are formed on the current confinement layer (27). A cap layer (28) made of GaAs is also formed by MOCVD. Then, on the cap layer (28), one electrode (2
9) Deposit and form the other electrode (30) and cap (21)
Ohmic deposition is formed on the back surface of.

In this way, a semiconductor laser can be obtained. That is,
In this case, when a forward voltage is applied between the electrodes (29) and (30), at the portion where the radio wave confinement layer (27) exists, that is, on both sides of the removed portion (27a), so to speak in the thickness direction, p
Since the -n-p-n switching element is formed, the flow of the current is limited here, and the current is concentrated in the diode part formed between the electrodes (29) and (30) through the removing part (27a). The removal part (27a) of the active layer (24)
Luminescence occurs below. A gain guide type semiconductor laser is constructed in this manner. Now, in the configuration of FIG. 3, the width W of the removed portion (27a) is large, and the composition of the current confinement region (27) is, for example, p-. By selecting Al _x Ga _1-x As (x> 0.7), the energy band gap of the active layer (24) is smaller than that of the active layer (24) made of Al _0.52 ln _0.48 P. When the layer (27) is used as a light absorbing layer by largely selecting the refractive index for the light, the distance d between the active layer (24) and the layer (27) is set to be equal to that of the light from the active layer (24). This light can be absorbed by the light absorption layer (27) by selecting such that the light can reach the light absorption layer (27), for example, 0.2 to 0.5 μm, and by this, a portion facing the removal portion (27a) is formed. Since a built-in refractive index difference can be formed on both sides, it is recommended to use a refractive index guide type. It can also be. Alternatively, a semiconductor laser having both a gain guide type and a refractive index guide can be constructed by appropriately selecting the respective dimensions W and d.

In the example described above, the buffer layer (22) is provided to obtain good crystallinity in the light emitting mechanism section. However, in some cases, the buffer layer (22) may be omitted and the first crystal may be omitted.
The cladding layer (23) of the
It is possible to prevent the low crystallinity at the interface with 1) from affecting the crystallinity of the light emitting mechanism.

Further, in the above example, the protective semiconductor layer (26) is provided, but in some cases, it may be omitted.

MOCVD for forming each of the above semiconductor layers (22) to (28)
For example, triethylaluminum, triethylgallium, triethylindium, phosphine, and arsine are used as a source gas, and AlGalnP-based or AlGaAs-based epitaxy of each composition can be performed by adjusting the supply amount of these. Further, in the above-mentioned example, the respective layers (21) to (28) and (37) are formed by MOCVD, but they may be formed by a well-known MBE.

Further, in the above-mentioned example, in the case of obtaining a double heterojunction type semiconductor laser, other various semiconductor lasers, for example, a semiconductor laser having a light emitting mechanism portion by a quantum well, so-called QW (Quantum Well) type or MQW ( Mul
The present invention can be applied to a ti Quantum Well) type semiconductor laser.

[Effects of the Invention] As described above, according to the present invention, the light emitting mechanism is formed by the organic metal or metal vapor phase epitaxy method of the AlGalnp-based semiconductor before the unevenness processing is performed. For example, epitaxy can be performed on 100 crystal planes, and despite using the AlGalnP system, good crystallinity can be obtained at least in the part directly contributing to light emission, and a stable semiconductor laser with good characteristics can be obtained. Is something that can be done.

[Brief description of drawings]

1 to 3 are process diagrams of an example of a method for manufacturing an AlGalnP-based semiconductor laser according to the present invention, and FIG. 4 is a schematic enlarged sectional view for explaining the conventional manufacturing method. (21) is a substrate, (23) is a first buffer layer, (24) is an active layer, (25) is a second cladding layer, and (27) is a current confinement layer.

Claims (2)

[Claims] 1. An AlGa having at least a first cladding layer, a flat active layer, and a second cladding layer.
In the InP-based semiconductor laser, a semiconductor layer having a function of current confinement and having irregularities having a (111) crystal plane on the side surface is provided on the second cladding layer, and AlGaAs or AlGaAs An AlGaInP-based semiconductor laser having a GaAs-based semiconductor layer formed thereon. 2. A step of forming a flat AlGaInP based semiconductor layer for forming a first cladding layer, an active layer and a second cladding layer by an organic metal or metal vapor phase epitaxy method, and the second cladding. A step of forming a semiconductor layer on the layer, and subjecting at least the semiconductor layer to a concavo-convex process having side surfaces having a (111) crystal plane to form a current confinement function part; And a step of forming an AlGaAs or GaAs-based semiconductor layer by a phase growth method.