JPS63164374A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To prepare a semiconductor laser device having high reliability, holding high productivity and reproducibility by forming a current constriction layer consisting of InGaAlP through a contact layer composed of GaAs, InGaP, etc. CONSTITUTION:An n-GaAs buffer layer 12 is shaped onto an n-GaAs substrate 11. A double hetero-junction structure section made up of an n-InGaAlP clad layer 13, an InGaP active layer 14 and a p-InGaAlP clad layer 15 is formed onto the buffer layer 12. A p-InGaP contact layer 16 and a p-GaAs contact layer 17 are shaped onto the clad layer 15. An InGaAlP current constriction layer 18 in which an opening section is formed to a section as a current path is shaped onto the contact layer 17. A p side electrode 19 is formed onto the current constriction layer 18 and the contact layer 17 exposed in the opening section, and an n side electrode 20 is shaped under the substrate 11. Currents can be constricted excellently by the current constriction layer 18, and a light- emitting region in the active region 14 is specified to a striped shape, thus allowing laser oscillation.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to semiconductor laser technology, and in particular to InGa laser technology.
The present invention relates to an AlPGaAl device and a manufacturing method thereof.

(Prior Art) InGaAiP has the largest bandgap among m-v group compound semiconductors, and is therefore attracting attention as a material for semiconductor lasers that oscillate at short wavelengths. In particular, a semiconductor laser with a GaAs substrate, a cladding layer of InGaANOP that is lattice matched to the GaAs substrate, and an active layer of InGaP is 600
It has an oscillation wavelength in the ns+ band, and is important as it can be used as a visible light semiconductor laser in a variety of ways as an alternative to He-Ne gas lasers.

In order to shorten the wavelength and improve the reliability of semiconductor lasers, it is necessary to have a bandgap energy that is sufficiently larger than that of the active layer where radiative recombination actually occurs, and to effectively confine injected carriers within the active layer. It is important that there is a cladding layer that can

In an InGaP active layer that is lattice matched to GaAs, its bandgap energy increases as the AI composition increases, making it desirable as a cladding layer material.

However, in InGaAJP, which has p-type ring conductivity in aAIPSCt in In, it becomes difficult to lower the resistance as the bandgap energy increases. The present inventors have developed a high-A composition InGaA nanoP with a bandgap of 2 J oV or more, which is lattice matched to a GaAs substrate and has a band gap of 2 J oV or more, using a metal organic pyrolysis vapor deposition method (hereinafter abbreviated as MOCVD method).
The p-type doping experiment was repeated for . the result,
The resistivity that can be achieved while maintaining good crystallinity is 0.7Ωa.
It turns out that this is all.

Furthermore, in manufacturing a semiconductor laser, it is important to be able to form electrodes that make ohmic contact.

However, it is very difficult to form a direct ohmic contact to the InGaAiP cladding layer.

Coreha, InGaA, i? This is thought to be due to circumstances such as the extremely large band gap of P and the difficulty in doping at a high concentration, especially in p-type. For this reason, InGaAl! A method has been considered in which ohmic contact can be easily established by providing a highly doped contact layer made of InGaP, GaAS, or the like on the P cladding layer.

Now, taking into consideration the need for a highly doped contact layer on the InGaAIP cladding layer, let us consider the current confinement of this laser. In the following discussion, we will proceed assuming that the contact layer is p-type, but the situation is the same even if it is n-type.

5i02. on the p-type contact layer. A method has been reported in which an insulating film such as Si3N4 is formed and current confinement is performed using this film. FIG. 3 shows a 5i02 stripe laser using 5i02 as an insulating film. In the figure, 31 is an n-GaAs substrate, 3
2 is an n-I nGaA-P cladding layer, 33 is an InGaP active layer, 34 is a p-1nGaA-P cladding layer, and 35 is a p-G
aAs contact layer, 36 5i02 insulating film, 37 p
The side electrode 3B is an n-side electrode.

In this laser, after a double heterostructure is created by the first crystal growth using the MOCVD method, a 5i02 film 36 of about 1000 layers is formed by a sputtering method, etc., and then formed into a stripe shape by etching using a photomask. 5
This is achieved by removing the iO2JII 36 and then forming the electrodes 37,38. The above steps are relatively easy and have excellent reproducibility.

However, the laser having the structure shown in FIG. 3 has the following problems. That is, if the p-GaAs contact layer is doped at a high concentration in order to obtain good ohmic contact, its specific resistance becomes extremely small (below 0.1 Ωn). On the other hand, the specific resistance of the p-InGaA, 17P cladding layer is as high as 0.7Ωα or more, so the current is
C: The aAs contact layer spreads significantly in the lateral direction, resulting in an increase in threshold current. In order to prevent this, it is effective to make the p-GaAs layer thin, and making the p-GaAs layer thin is also effective in dissipating heat in the active layer to the p-side electrode. However, S i
The insulating films such as 02, S i3 N4, etc. are GaAs.

Since its thermal conductivity is lower than that of a semiconductor crystal such as InGaA, a laser using this type of insulating film cannot solve the problem of an increase in the temperature of the active layer during direct current operation.

On the other hand, a laser having a structure as shown in FIG. 4 has been proposed by performing crystal growth by MOCVD twice or more. In the figure, 41 is an n-GaAs substrate, 42 is an n-
1nGaA P cladding layer, 43 InGaP active layer,
44 is p-I nGaA P cladding layer, 45 is p-G
aAs first contact layer; 46, n-GaAs current confinement layer; 47, p-GaAs second contact layer; 48°49
is an electrode.

This laser is formed by forming an n-GaAs current confinement layer 4 on an n-GaAs substrate 41 during the first crystal growth using the MOCVD method.
6, the n-GaAs current confinement layer 46 is etched into stripes by etching using a photomask, and the p-GaAs second contact layer 47 is formed by the second crystal growth using the MOCVD method. This is what I did. The p-GaAs first contact layer 45
AI during the second crystal growth! This is to prevent the influence of an oxide film etc. due to exposing the surface containing the oxide.

However, the laser having the structure shown in FIG. 4 has the following problems. That is, since the n-GaAs layer, which is opaque to the emission wavelength, is used for current confinement, its thickness is reduced to 1
It must be thicker than approximately μm. This is to prevent the phenomenon that the current confinement layer is excited by light seeping into the current confinement layer and short circuit occurs when the current confinement layer is thin, that is, turn-on due to light. Therefore, the second crystal growth must be performed on a large step, making it difficult to obtain a good crystal.

Also, due to the same circumstances as the 5i02 stripe laser,
It is desirable that the p-GaAs first contact layer be thin, but if this layer is thin, the n-GaAsf! ! When etching the flow constriction layer, it is necessary to precisely control the etching depth, which may cause problems in uniformity and reproducibility. Furthermore, having to perform crystal growth by MOCVD twice may cause problems in productivity, reproducibility, and the like.

In addition, in the structures shown in Figs. 1 and 4, a structure in which the p-side electrode is directly formed on the step without forming the p-GaAs second contact layer has been proposed for a GaAlAs double hetero laser. There are still problems such as controllability and electrode breakage due to formation of electrodes on large steps.

(Problems to be Solved by the Invention) As described above, conventional lasers using an insulating film as a current confinement layer have poor heat dissipation properties and cannot achieve even better current confinement. Further, a laser using GaAs as a current confinement layer has a large step difference in the current confinement layer, resulting in problems such as deterioration of crystal quality and generation of step breakage. Furthermore, since the contact layer cannot be made thin, good current confinement cannot be achieved. In other words, with the conventional technology, InGaAJ! satisfies both good current confinement and good heat dissipation characteristics, maintains high reproducibility, and has high reliability! It has been extremely difficult to realize a P-based semiconductor laser.

The present invention has been made in consideration of the above circumstances, and its purpose is to be able to obtain good current confinement and good heat dissipation characteristics even in a semiconductor laser having an InGaA nanoP cladding, and to reproduce the same. An object of the present invention is to provide a semiconductor laser device that can improve performance and reliability.

Another object of the present invention is to provide a method for manufacturing a semiconductor laser device for easily manufacturing the semiconductor laser device.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is that InGaAl! In a semiconductor laser having a P cladding layer, GaAs.

InGaAl through a contact layer such as InC;aP
! By providing a current confinement layer made of P, it is possible to create a device with high reliability while maintaining high productivity and reproducibility.

That is, in the present invention, the active layer is made of InGa AJ! P (0≦x, y≦1) or 1
a double heterojunction structure sandwiched between cladding layers of -x-y y x;
A double hetero structure type comprising a current confinement layer provided with striped openings forming a current path, and a contact layer disposed between the double heterojunction structure and the current confinement layer. In the InGaAiP laser, the current confinement layer is made of In, Ga, AI, P(0
≦X'', y'≦1-x-y y x 1), and the contact layer is made of Ga
As (0≦2≦1) and 1-z z In Ga As P (0≦u, v≦1
) 1-u u l-v v .

Further, the present invention provides a method for manufacturing a semiconductor laser device for realizing the above structure, in which an active layer is formed on a compound semiconductor U plate by InGaAIP(01-xy
After forming a double heterojunction structure sandwiched by cladding layers consisting of y and I'n Ga As P
A contact layer made of at least one of l-u l-v v (0≦U, V≦1) is formed, and then In, In,
Ga, AI! , P(0≦X', y'≦1)1-x-
In this method, a current confinement layer consisting of y y x is formed, and then this current confinement layer is etched into stripes by selective chemical etching using a photomask.

(Function) According to the present invention, unlike insulating films such as 5i02 and Si3N4, InGaAl! has high thermal conductivity! Since P is used as the current confinement layer, heat generated in the active layer can be effectively released to the electrode side through the current confinement layer. Furthermore, since InGaA and j'P, which are current confinement layers, are transparent to the emission wavelength, turn-on and the like will not occur due to light even if this layer is made thin. Therefore, it is possible to reduce the step difference in the current confinement layer, and the electrodes and contact layers formed thereon can be formed satisfactorily. Furthermore, as a contact layer, l nGaA
If a material with high AI switching selectivity (such as GaAs) is used, it is possible to make the contact layer sufficiently thin.

Therefore, I n G a A l! Even in a semiconductor laser having a P cladding layer, it is possible to realize a semiconductor laser that has a simple structure that can achieve high productivity, and has good current confinement and heat dissipation that can achieve high reliability.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a sectional view showing a schematic structure of a semiconductor laser according to an embodiment of the present invention. In the figure, 11 is an n-GaAs substrate, and on this substrate 11 is an n-GaAs /
<A buffer layer 12 is formed. On the buffer layer 12 is an n-1nGaAIP cladding layer 13. A double heterojunction structure consisting of an InGaP active layer 14 and a p-InGaAJP cladding layer 15 is formed. On the cladding layer 15 is a p-InGa P:2 contact layer 16.
and a p-GaAs contact layer 17.

On the contact layer 17, an InGaA PAI constriction layer 18 is formed which has an opening in a portion that will become a current path. A p-side electrode 19 is formed on the current confinement layer 18 and the contact layer 17 exposed at the opening thereof, and an n-side electrode 20 is formed under the substrate 11.

The conductivity type of the current confinement layer 18 may be n-type, high resistance, or lightly doped p-type.

With such a configuration, the current confinement layer 18 provided with stripe-shaped openings can perform good current confinement, and the light emitting region of the active layer 14 can be defined in a stripe shape to perform laser oscillation. You can make it happen.

Here, the effect of using InGaA as the AI constriction layer is explained by the following mechanism. That is, ohmic contact between InGaA PA and AI metal is difficult, and moreover, 1 nGaA PA
I has a high resistance and it is difficult to pass current through it. Moreover, InGaAJ! has a band gap larger than the energy of the emission wavelength of the semiconductor laser! By using P as a current confinement layer, turn-on by light can be prevented. In reality, several of these things occur simultaneously, so the current confinement effect is greater than when the current confinement layer is made of n-GaAs or the like.

For the above reasons, even when the thickness of the current confinement layer 18 is reduced to 0.5 μm or less, the current confinement effect is sufficient, and when an electrode is provided on the layer, problems such as step breakage are unlikely to occur. Furthermore, even in the case where the second p-GaAs contact layer is provided on a part of the contact layer 17 and the current confinement layer 18 and the electrode is formed thereon, without directly forming an electrode, if the step is small, the crystalline There is almost no damage to it.

In addition, a current confinement layer made of InGaA and 1'P is
Compared to those using insulating films such as 5i02 and Si3N4, it has a higher thermal conductivity, so it has the advantage of being able to prevent the temperature of the active layer 14 from rising. Furthermore, when GaAs is used as the contact layer, InGaAJ! as the current confinement layer! Since etching selectivity can be made sufficiently high compared to P, it is possible to reduce the thickness of the contact layer. This is effective for reducing current spread in the contact layer and achieving good current confinement.

Next, regarding the manufacturing method of the semiconductor laser having the above structure, m
This will be explained with reference to FIGS. 2(a) to 2(C).

First, as shown in Figure 2(a), n of the plane orientation (100)
-N-Ga is deposited on the GaAs substrate 11 by the MOCVD method.
As buffer layer 12. n-I nGaA NoP cladding layer 13. InGaP active layer 1
4. p-1nGaA P cladding layer 15. p-InGa
P contact layer 16. A p-GaAs contact layer 17 and an undoped InGaAiPfli flow confinement layer 18 were sequentially grown to form a double hetero wafer. At this time,
The thickness of the p-1nGaP contact layer 16 was set to 500 Å or less, and the thickness of the p-GaAs contact layer 17 was set to 1000 Å or less, thereby preventing the current from spreading in the lateral direction. Furthermore, the p-1nGaP contact layer 16 has the role of facilitating current conduction between the cladding layer 15 and the p-GaAs contact layer 17.

Next, as shown in FIG. 2(b), a photoresist is coated on the current confinement layer 18, and this is exposed and developed to form a photomask 2 having striped openings.
1 was formed.

Then, by selective chemical etching using H3PO4 at 60°C, 1nGaAiP was etched as shown in Figure 2(C).
Only the current confinement layer 18 is removed in stripes. Here, the etching speed of the GaAs and InGaP layers by this etchant is extremely slow, and only the InGaAsP layer can be selectively etched easily.

After this, after removing the photomask 21, by forming an A u / Z n electrode 19 on the p side and an A u / G e electrode 20 on the n side as electrode metals,
A laser having the structure shown in FIG. 1 is completed.

According to this manufacturing process, since the etching selectivity between the contact layers 16 and 17 and the current confinement layer 18 is extremely high, there is no need to precisely control the etching depth, and the current confinement structure can be easily created. Furthermore, since the process of forming a 5LO2 film, which is necessary when forming a 5i02 striped laser, is not included, the productivity can be greatly improved.

Note that the present invention is not limited to the embodiments described above. For example, the material for the active layer is not limited to InGaP, but may be lattice-matched to the GaAs substrate and whose band gap energy is equal to that of the cladding layer.
Any material that is smaller than iP (0≦x, y≦1) may be used, such as InG or aAsP.

GaAl! As, etc. can be used. In addition, as examples of using p-1nGaP and p-GaAs as contact layer materials, only one of them or G
It may be aA, As, or InGaAsP. moreover,
It is also possible to use InGaP instead of InGaA and 17P as the material for the current confinement layer.

In addition, in the example, a structure with high productivity that can be created by one epitaxial growth is shown, but the current confinement effect is also sufficient by providing a p-GaAs contact layer under the p-side electrode by a second epitaxial growth. .

Furthermore, it is also possible to realize a laser using p-GaAs as a substrate and having the conductivity types of each layer reversed. In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, InGaAl! Even in semiconductor lasers with P as the cladding layer, by using the InGaA12 layer as the current confinement layer, good current confinement and heat dissipation are possible.
It can be realized with reproducibility, and its usefulness is great.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the schematic structure of a semiconductor laser according to an embodiment of the present invention, M2 is a cross-sectional view showing the manufacturing process of the above laser, and FIGS. 3 and 4 each show the schematic structure of a conventional laser. FIG. 11-n-GaAs substrate, 12-n-G
a As buffer layer, 13...n-1nGaAnoP
Cladding layer, 14-1 n GaP active layer, 15
...p-1nGaAJ! P cladding layer, 16...
p-fnGaP contact layer, 17...p-GaA
s contact layer, 18...InGaAJ! P current confinement layer, 19.20--electrode, 21--photomask. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (3)

[Claims] (1) Active layer is In_1_-_x_-_yGa_yAl
A double heterojunction structure sandwiched between cladding layers consisting of _xP (0≦x, y≦1) and a striped opening formed on one side of this double heterojunction structure to form a current path are provided. In_1_−_x′_−_y′Ga_y′Al_x′P
(0≦x', y'≦1), and is arranged between the double heterojunction structure and the current confinement layer, and Ga_1_-_zAl_zAs (0≦z≦1) and In
_1_-_uGa_uAs_1_-_vP_v(0≦u
, v≦1). (2) The contact layer is a first conductivity type layer, and the current confinement layer is a second conductivity type layer, a high resistance layer, or a lightly doped first conductivity type layer. A semiconductor laser device according to scope 1. (3) On the compound semiconductor substrate, form the active layer In_1_-_x_-_yGa_yAl_xP(0≦x
, y≦1), and Ga_1_-_zAl_zAs(0≦z≦1) on the double heterojunction structure.
) and In_1_−_uGa_uAs_1_−_vP_
a step of forming a contact layer consisting of at least one of v (0≦u, v≦1), and forming a contact layer made of at least one of
0≦x', y'≦1); and a step of etching the current confinement layer into stripes by selective chemical etching using a photomask. A method for manufacturing a semiconductor laser device.