JPS6373581A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser, which has small oscillation threshold current density, generates single transverse mode oscillation and can be manufactured with excellent yield in a uniform large area, by specifying a buried semiconductor layer from the periodic table and changing the semiconductor layer into a semi-insulating compound semiconductor layer. CONSTITUTION:When a II-VI compound semiconductor layer 103 consists of ZnSl, it has index difference extremely larger than the refractive index of an active layer 109 composed of GaAs, etc., and the efficiency of optical confinement is improved, thus lowering injection current density. Since a II-VI compound semiconductor has an extremely large band gap, the resistivity of a thin-film through an MOCVD method is increased, and the buried layer 103 can prevent inJection currents completely. Consequently, threshold current density can further be lowered. The active layer 109 is inverted-mesa-etched in a striped manner, and the buried layer 103 is shaped, thus acquiring a flat surface. The width of the actual active layer 109 is made narrower than that of a resist pattern in a photolithographic process, thus resulting in a single oscillation transverse mode, then allowing stable laser operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a semiconductor laser with low threshold current density and single mode oscillation.

[Conventional technology]

In a semiconductor laser, in order to obtain a stable laser with a low threshold direct current density and a single transverse mode, a method is used in which both ends of the active layer are buried with a semiconductor material whose refractive index is smaller than that of the active layer. It is being

The construction of the conventional embedded semiconductor laser was published by Journal Kenop Applied Physics (J, AppA, P
Ays, 45, 4899 (1974)).

Both sides of the oscillation region A7'0-070 (Lo, 9IA8 layer are filled with A7'<1.5 saao, ES layer 8 layers, and the same ■-■ This was done by using family-based materials and embedding semiconductors with different configurations.

A typical structure thereof is shown in FIG.

Further, the buried layer of a conventional buried laser has been manufactured by a liquid phase epitaxial method (hereinafter referred to as LPE method).

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional technology, since the specific resistance of the buried layer is low, the carriers injected into the active layer diffuse, and the loss of the injected carriers is large, making it difficult to reduce the threshold direct current density for one oscillation. Nine.

Since the same ■-V group system is used, the difference in refractive index between the active layer and the active layer is only about 5 degrees, which has the problem of poor lateral optical confinement and high single-laser threshold perpendicular flow density. Do it.

Furthermore, the growth method of the semiconductor layer.

LP! Since it is a method, it is difficult to grow uniformly over a large area, and as a result, there is a problem in that the defect rate within the wafer is high.

Therefore, the present invention aims to solve these problems.
Its purpose is to determine the oscillation threshold direct current density.

The object of the present invention is to provide a semiconductor laser which has a small power, oscillates in a single transverse mode, and can be manufactured uniformly over a large area with a high yield.

[Means for solving problems]

The semiconductor laser of the present invention has a double heterojunction composed of a compound semiconductor layer made of elements of group (I) and group V of the periodic table as a cladding layer and an active layer, and both ends of the active layer are connected to the active layer. In a semiconductor laser embedded with a semiconductor layer having a small refractive index (with a refractive index of It is characterized by being t-characteristic.

Further, the active layer is characterized in that the buried semiconductor layer is formed after reverse mesa etching in a stripe shape.

Further, all the semiconductor layers constituting the semiconductor laser T- are manufactured by the Moavp method.

[Effect]

According to the above configuration of the present invention, the n-w group compound semiconductor layer has a refractive index of GcL at 238 g, for example.
At the oscillation wavelength of the active layer of AI etc., 2.51
Since the refractive index of the active layer is about 3.59 to . 3.
It has a very large refractive index difference compared to 49. Therefore, the light confinement effect in the plane direction of the active layer is AJG (
Since the light confinement efficiency is significantly higher than in the case of embedding with a 1li-V group compound semiconductor layer such as zAj, the injection current density required for laser oscillation conditions can be lowered.

Further, the 1-M group compound semiconductor is, for example, Z%B.

In this case, the band gap is as large as 2.8 gV.

Therefore, when a highly pure single crystal thin film is grown using the MOCVD method, the specific resistance of the thin film is 10'Ω.
A buried layer made of an a, II-M compound semiconductor having a thickness of 1 m or more can completely block the injection current.

Therefore, there is no diffusion of carriers other than the active region of the injection current, and the injection current can be completely confined within the active region.

As a result, the threshold current density can be further reduced. In addition, since the buried layer is formed after the active layer is reverse mesa-etched into stripes, there is no abnormal protrusion growth on the surface of the buried layer, and a flat surface can be obtained, allowing the upper electrode to be formed. In some cases, problems such as electrode breakage do not occur.

Furthermore, since reverse mesa etching is used, the actual active layer width is narrower than the resist pattern width in the photolithography process, and an active layer width of 0.5 .mu.m to 1.0 .mu.m is possible. As a result, the single oscillation transverse mode becomes single, allowing stable laser operation.

[Implementation row] FIG. 1 shows an implementation row of the present invention. It is a main cross-sectional configuration diagram of an embedded semiconductor laser, and is an n-type Gc of (102).
LA8 On the single crystal substrate (107), the shape Gα 8
Buffer layer, nllm IAaA# of (108) Cladding layer, non-doped GcLa6 or AJG of (109), zAg P-type mulch of active layer (105), P to G (zA5 contact layer of cladding layer (106)) It is structured in the shape of an inverted mesa.

Furthermore, both ends of it are (103) semi-insulating zBs 6
embedded in layers. A P-type ohmic electrode (104) is formed at the upper end, and an external ohmic electrode (101) is formed at the lower end. When a forward current is passed between the (104) and (101) electrodes, electrons are generated in the active layer part of (109).
Holes are injected and laser oscillation occurs. Since the buried layer of (103) is a semi-R stone, no current flows except for the fine active layer part of (109), and the laser oscillation light is emitted.

It glowed in spots. In addition, the active layer of (109) and the active layer of (10
Since there is a refractive index difference of 28 or more at the interface of the buried layer 3), almost no light seeps into the (103) buried layer.

Next, the manufacturing process of the semiconductor laser according to the present invention will be explained with reference to FIG. In chopsticks figure 2 (tL) (201)
The outer mold of GCLA8 single crystal substrate is H,EiO4:
H! A clean surface is prepared using an etching solution of o〒+:1:1'4.

After that, the susceptor was placed on top of the reaction tube of the MOCVD device, and 7 layers of n-type GQA4 buffer (202) (2
03) Outer mold A11) aAs cladding layer, (20
4) non-doped G (zA4 or A#aA a
An active layer, p+aGaAJ contact layers (206), and (206) are sequentially laminated in one growth. after that,
p by methods such as plasma C'7D method and atmospheric pressure CVP method,
870$ 56nz etc. form the insulation II (207) (Fig. 2 (6)), the insulation layer of (207),
s2 ~ lO by normal photolithography process
It is etched so that it remains in a stripe shape with a width of μm (
(Fig. 2 (6)), using this insulating film as a mask.

"!"04: us's: Hs O=4:1
: Etch using a No. 1 etching solution until the GcLhH substrate (201) is exposed.

In this case, the insulating layer stripes (20?) are formed by selecting a direction in which reverse mesa etching is possible in the cross section perpendicular to the longitudinal direction. The wafer subjected to the first inverse mesa etching process, which leaves one active layer (204) in the shape, is placed again in the MOCVD apparatus and a Z%B g thin film of (208) is grown. 275℃~400
The reaction was carried out at a reaction pressure of 5 to 50 Torr. (2
There is nothing to deposit on the insulating film of 07), and selective buried epitaxial growth is possible.
g The specific resistance of the thin film was more than to'Ω,α (Figure 2 (g)), and then as shown in Figure 2 (g), it was (20
Etching the insulation V& in 7) yields a flat plane.On the primary side, a P-type ohmic electrode (209) and an N-type ohmic electrode (210) are formed on the lower side, and the stripe is aligned in the longitudinal direction. A resonator is formed between the walls in a direction perpendicular to (ω in Fig. 2)).

The relationship between the oscillation output and the injection current of the semiconductor laser thus obtained is shown in FIG. 3. (301) is a line of output-current characteristics of the semiconductor laser in the example of the present invention. (302) is a series of output-current characteristics of an embedded laser obtained by conventional quantities.
The optical confinement and current confinement efficiency were improved, and the oscillation direct current density was reduced and the external differential efficiency was improved.

FIG. 4 shows a far field pattern (hereinafter referred to as ?FP) of a semiconductor laser in one embodiment of the present invention.
(401) is the active layer width of 0.8 mm, (402) is the active layer width of 1.0 μm, and (403) is 77P when the active layer width is 1.5 mm. In both cases, a single-peak pattern was obtained, and fundamental transverse mode oscillation characteristics were obtained.

〔Effect of the invention〕

As described above, according to the present invention, the current density is low, so that the heat generation of the semiconductor laser can be kept low. This K has a great effect on improving the life of the semiconductor laser. Further, since the bonding surface can be mounted on a heat sink with the bonding surface facing upward, it has the effect that mounting on an integrated type circuit board or the like becomes extremely easy. Furthermore, according to the present invention, since the growth temperature of the N-W group compound semiconductor layer is as low as 400° C. or less, there is less thermal influence on the active layer that is grown first and the laser characteristics are stabilized. . Furthermore, all semiconductor layers are manufactured by MOCVD.

It has the advantage of being able to be manufactured uniformly over a large area and having an extremely long lifespan.

[Brief explanation of the drawing]

FIG. 1 is a main sectional view showing an embodiment of the semiconductor laser of the present invention. FIGS. 2 μ) to 2 are manufacturing process diagrams showing an embodiment of the semiconductor laser of the present invention. 3 is a diagram showing the relationship between optical output and injection current of an embodiment of the semiconductor laser of the present invention. FIG. 4 shows F? of an embodiment of the semiconductor laser of the present invention. It is a figure showing P. FIG. 5 is a main cross-sectional view showing one row of conventional semiconductor lasers. (101), (210)e(501)...n-type ohmic electrode (102), (201), (502)...s
Type GQA3 substrate (103), (208) --ZnB-
Reasoning layer, (104)t(209), (509)・
・P-type ohmic electrode (105), (205), (50
6)--9 type AJGcLAj cladding layer (106), (
206)...p"fJI GaA3 contact layer (
107), (202) ---n type G (Bi2 buffer 7 layers (108), (203), (504)...n
Type AJG aA a cladding layer (109), (204)
, (505)...Active layer (207)...Insulating layer (301)...Z%B- Optical output characteristics of buried type semiconductor laser (302)...AIGaAa Optical output characteristics of buried type semiconductor laser ( 401)・Fist・FFF with active layer width 0.8 μm (402
)---Active layer width 1.0 tails OF F'? (403)
...F'1FF (503) with an active layer width of 1.5 steps...
Shape A haha buried layer (508)...insulating layer (507)...2 outer diffusion region toA lo! ; sheep 11i

Claims (3)

[Claims] (1) It has a double heterojunction composed of a compound semiconductor layer made of Group III and Group V elements of the periodic table as a cladding layer and an active layer, and both ends of the active layer have a refractive index of the active layer. A semiconductor laser embedded with a semiconductor layer having a smaller refractive index, characterized in that the embedded semiconductor layer is a semi-insulating compound semiconductor layer made of Group II and VI of the periodic table. semiconductor laser. (2) The semiconductor laser according to claim 1, wherein the buried semiconductor layer is formed after the active layer is reverse mesa-etched into a stripe shape. (3) All semiconductor layers constituting the semiconductor laser are
Chemical vapor deposition method (hereinafter referred to as MO) using organometallic compounds as raw materials
2. The semiconductor laser according to claim 1, wherein the semiconductor laser is manufactured by a CVD method.