JPH01166590A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To acquire a layer having a small light absorption index and a good junction reverse characteristics and to reduce optical loss and leak current of a window layer of a semiconductor laser by using an high concentration impurity added layer previously formed at a stage of crystal growth as a diffusion layer. CONSTITUTION:After an n-Ga0.5Al0.5 clad layer 2, a quantum well structure active layer 3, a p-Ga0.5Al0.5As clad layer 4, and an n-GaAs light absorbing layer 5 are caused to grow on an n-GaAs substrate 1 of a semiconductor laser, the layer 5 is selectively removed to form a striped pattern. The layer 4 in an area near a laser edge side is made thin a desired thickness by applying another photolithography and burying growth is carried out to form three layers of a p-Ga0.5Al0.5As layer 6, a p-Ga0.5Al0.5As layer 7 and a p-GaAs cap layer 8. Annealing at a desired temperature within a crystal growth furnace is conducted, and a crosswise and lengthwise cross sectional structure of laser stripe is formed. In this way, it becomes possible to control edge side deterioration caused by rising of a edge side structure due to light absorption of the edge side.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor laser formed using a compound semiconductor.

[Conventional technology]

A conventional semiconductor laser uses several A of Ga as shown in FIG.
The basic structure is a stacked quantum well-structured active layer of As and GaA Q As, and GaA Q As with a wide forbidden band and different conductivity sandwiched between these layers, and the quantum well active layer is mixed by impurity diffusion etc. Let it crystallize.

The changes in the refractive index and absorption coefficient of the active layer due to mixed crystal formation were used to form waveguides and to make the laser end face transparent.

[Problem that the invention seeks to solve]

In the conventional semiconductor laser described above, the concentration of impurity diffusion cannot be controlled and a layer with a very high impurity concentration is created.
There have been problems such as optical loss and leakage current in the window layer, and limited controllability of the depth of impurity diffusion, resulting in poor productivity.

An object of the present invention is to solve the above problems.

[Means for solving problems]

In order to solve the above problems, the present invention has invented a structure and manufacturing method for a semiconductor laser that produces the same results as the conventional technology by using a highly doped layer of impurities, which has been formed in advance at the crystal growth stage, as a diffusion source. .

[Effect]

According to the present invention, since the epitaxially grown layer whose impurity concentration can be easily controlled can be used as a diffusion source,
It is possible to obtain a layer with low light absorption and good junction reverse characteristics. Therefore, the drawbacks of the above-mentioned conventional structure are greatly improved.

〔Example〕

The present invention will be described in detail below with reference to the drawings.

Example 1 Example 1 of the present invention The structure described according to FIGS. 1 and 2 is based on an n-GaAs substrate (1) (Si doped, n=2X
10"δcm""M) by MOCVD method.
ao, aA Qo, bAs cladding layer (2) (Se
Doped, n = 1.5 x 1018c+a-”)
*' ffk well structure active layer (3) [G a
As well layer (9): 60A GaAQAs barrier layer (10): 30λ, p-G ao, sA Q
o, aAs cladding layer (4) (Mg doped, p =
I x 10"cm-"), n-G'a As
Light absorption layer (-5) (Se doped, n = 4 x 1
After growing 0 "cm-"), a striped 5iOz pattern was formed using normal photolithography technology, and active ion etching was performed to form n-Ga.
The As light absorption layer (5) was selectively removed and the p-GaO, FIAQO, FIAs cladding layers (
4) is approximately 0.2 pm, and p −G a o, sA Q
o, sA s layer (6) (Zn doped, p=5X101
gcm-3), p-G ao, FIA Q o, sA
s layer (7) (Zn doped, P=1×101'cn+-
'), p-G a As cap layer (8) (Zn
Doped, p = 5 x 10 "cs+-") three-layer buried growth was performed, and further, 9 layers were grown in a crystal growth furnace.
Annealing was performed at 00°C for 3 minutes.

The horizontal and vertical cross-sectional structures of the laser stripes formed through these steps are shown in FIGS. 1 and 2, respectively. The basic waveguide mechanism of this structure is similar to that of a so-called self-aligned laser, but since the Z'n diffusion layer passes through the active layer at the laser end facet, the quantum well structure in this part is destroyed and the forbidden band The end face becomes transparent to wide relay laser light. Therefore, the phenomenon of end face deterioration caused by the elevation of the end face structure due to light absorption at the end face is suppressed, and a highly reliable high power semiconductor laser can be formed.

Example 2 Example 2 of the present invention will be explained with reference to FIGS.
-G ao, sA Q o, sA s cladding layer (
2), quantum well structure active layer (3), p-G a
o, aA Q o, aA s cladding layer (4), n-G
After growing the aAs light absorption layer (5), a striped 5ins pattern is formed using normal photolithography technology, and n-G a A is formed by active ion etching.
The s-light absorption layer (5) is selectively removed, and the photolithography process is carried out again to form p-G ao, sA It
o, sA s cladding layer (4) with lens-like structure (11
) repeats along the stripe, as shown in Figure 3, and is etched by approximately 0.3 μm.
o, lIA Q o, sA s layer (6), p -G
a o * BA Q o, sA s layer (7), p -G
Buried growth consisting of three layers of aAs cap layer (8) was performed to form a structure as shown in FIG. The dopant and carrier concentrations of each layer were the same as in Example 1. Next, this structure was heated at 900°C while applying As pressure in an MOCVD apparatus.
A heat treatment was applied for 60 minutes. As a result, p-G ao,s
A Q o, aA s Zn in M (6) is re-diffused to mix the quantum well structure active layer (3). A lens is formed due to the difference in refractive index between the mixed crystal quantum well and the unmixed quantum well.

Moreover, in the case of the example, when there is no light absorption in the active layer of the lens part and hole burning occurs, the difference in refractive index between the lens part and the part other than the lens becomes larger and the effect of preventing hole burning is strengthened. The curvature of the lens can be made smaller, which is advantageous in terms of normal laser characteristics. The radius of curvature of the lens is R215μm, the distance of the lens is d=10
When the stripe width is 10 μm, a semiconductor laser that oscillates in a stable transverse fundamental mode up to an optical output of 200 mW was obtained using a device with a stripe width of 10 μm.

Example 3 Example 3 of the present invention will be explained with reference to FIGS. 3 and 5. n-Gao, 6A Qo, aAs cladding layer (2), quantum well structure active layer (3), p-Gao were formed on the n-GaAs substrate (1) by MOCVD method.
, aA 11 o, nAs cladding layer (4), n-G
After growing the aAs light absorption layer (5), two striped 5iOz patterns were formed in parallel using normal photolithography, and only the stripes were etched by active ion etching. Q o,
The ISA cladding layer (4) was etched by about 0.3 μm. Then p + G a o, aA Q O, RA
8 layers (6), p-Gao, 5AQo, r+AsM
(7) and a P GaAs cap layer (8) were buried and grown to form a structure as shown in FIG. The dopant and carrier concentrations in each layer were the same as in Example 1. Next, this structure was heat-treated at 900° C. for 60 minutes while applying As pressure in an MOCVD apparatus. This result p
-G a O, FIA Q O, FIA Zn in the 8 layer (6) is re-diffused to mix the quantum well structure active layer (3). As a result, as shown in Figure 5, the emission wavelengths of the two stripes are different due to the difference in the forbidden band width of the mixed crystal quantum well and the unmixed quantum well, so lasers with different wavelengths are integrated on the same substrate. We were able to.

〔Effect of the invention〕

According to the present invention, the window layer has low optical loss and leakage current.
A semiconductor laser with good characteristics and high productivity can be provided.

[Brief explanation of the drawing]

1 is a cross-sectional structural diagram of a semiconductor laser according to Example 1 of the present invention, FIG. 2 is a cross-sectional structural diagram in the stripe direction of the semiconductor laser according to Example 1 of the present invention, FIG. 3 is a structural diagram of a lens-like structure, and FIG. 4
The figure is a cross-sectional structural diagram of a semiconductor laser according to a second embodiment of the present invention, and FIG. 5 is a cross-sectional structural diagram of a semiconductor laser according to a third embodiment of the present invention.
FIG. 6 is a structural diagram of a conventional semiconductor laser. 1- n -Gr+As substrate, 2- n -Gao, a
A Q o, nAs cladding layer, 3... quantum well structure active layer, 4... p-G a o, aA Q o, aA
s cladding layer, 5- n-GaAs light absorption layer, 6-
p+ Gao, 5AQo, aAs layer, 7 ・p-G a
o, IIA Q o, aA s layer, sp GaA
s layer, 9-GaAs well layer, 10-G
ao, sA Q o, zAs barrier layer, 11... Lens-like structure, 12... Zn diffusion region, 13... Laser stripe, 14... p-rich 1 Figure Z Figure 3 4 Figure 5 Figure 5 Final figure

Claims (1)

[Claims] 1. It has at least a superlattice layer formed by laminating one or more periods of semiconductor layers of different compositions with a thickness of several hundred Å or less, and a layer doped with impurities that easily diffuses near at least a part of the superlattice. A method for manufacturing a semiconductor laser, characterized in that the superlattice layer is provided with a desired refractive index or forbidden band width distribution by utilizing mixed crystal formation of the superlattice due to the diffusion of impurities from the impurity doped layer.