JPH02206191A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To simplify the structure of the lateral-mode controlled InGaA P semiconductor laser of the title device and improve the yield of the laser by incorporating a diffraction grating in the laser. CONSTITUTION:An n-GaAs substrate 10, n-In0.5(Ga0.3A0.7)0.5P clad layer 11, non- doped lnGaP active layer 12, p-In0.5(Ga0.7A0.3)0.5P optical waveguide layer 13, current blocking layer 14, p-In0.5(Ga0.3A0.7)0.5P clad layer 15, p-GaAs contact layer 16, and diffraction grating 17 are provided. Since the built in diffraction grating 17 amplifies only rays of light in the direction of a resonator, a lateral- mode controlled laser which stably oscillates in a single longitudinal mode can be obtained. Therefore, a laser which is simple in structure and has good characteristics can be obtained in high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a semiconductor laser device used as a light source for optical information processing, optical measurement, etc., and a method for manufacturing the same.

(Prior Art) In recent years, short wavelength semiconductor lasers have been developed for application to high-density optical disk systems, high-speed laser printers, barcode leagues, and the like. Among these, the InGaA I P red laser, which has an oscillation wavelength in the 0.6 μm band, has the potential for various applications as an alternative to the conventional He-Ne gas laser, and has the potential to be used as a compact laser in the fields of optical information processing and optical measurement. , is attracting attention as a key device for realizing light sources that are lightweight and have low power consumption.

Among the above applications, applications other than barcode readers require a transverse mode controlled laser that oscillates in the fundamental transverse mode. As such a transverse mode control InGaAIP laser, a ridge stripe type SBR as shown in Fig. 9 is used.
Laser (Extended Abstracts, 19t
h Conf, 5olid 5tate Device
s and Materials, Tokyo (198
7), ppH 5-118). This laser can obtain a fundamental transverse mode by selecting appropriate structural parameters. However, regarding the longitudinal mode, since the cleavage plane of the crystal is used as a laser resonator, a plurality of longitudinal modes oscillate. Therefore, in the field of optical measurement that requires a specific wavelength, a laser that oscillates in a single longitudinal mode is required. In order to oscillate in a single longitudinal mode,
Distributed feedback type using a diffraction grating
Feedback: DFB for short) laser or distributed reflective type (Distributed BraggRel)
'1eetor: DBR for short) has a laser, and In
It has been developed for 2-based and GaAs-based semiconductor lasers.

InGaAIP is a structure that oscillates in a single longitudinal mode.
In order to employ this system in a transverse mode controlled SBR laser, a diffraction grating must be created inside the laser. Therefore, if chemical vapor deposition using an organic metal is used, the number of crystal growth will be four. This was a very big disadvantage when considering the simplification of the laser manufacturing process, yield, and cost reduction.

(Problem to be Solved by the Invention) As mentioned above, in the conventional device, since the laser is a Fabry-Perot type laser in which the interfold surface is used as a laser resonator, even though the transverse mode is controlled, the longitudinal mode is not. However, it has been difficult to achieve stable single longitudinal mode oscillation. Furthermore, in order to realize a single longitudinal mode in a transverse mode controlled SBR laser, the number of crystal growths was four times, resulting in a very poor yield.

This invention was made in consideration of the above-mentioned problems, and its purpose is to provide a transverse mode control InGaAIP-based semiconductor device that stably oscillates in a single longitudinal mode with only two crystal growths, and a method for manufacturing the same. It's there.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to provide a new transverse mode control I with a simple structure.
By incorporating a diffraction grating into an nGaA I P semiconductor laser, stable single longitudinal mode oscillation is possible. That is, the present invention is directed to the first conductivity type In
(GaAl)P.

0.5 1-z z O,5In (G
a Al ) P, second conductivity type 0.5
1-x x O,5In (Ga Al
) P optical waveguide layer 0.5 1-yyO,
5. A current blocking layer is formed on the double heterostructure portion and the surface of the double heterostructure excluding the stripe portion, and the stripe portion of the second conductive type optical waveguide layer is provided with periodic irregularities, A second conductivity type 1no, 5 (GaAl) P cladding layer (0≦X1−z x O,5 y<z≦1) and a second conductivity type contact are formed on the second conductivity type optical waveguide layer and the current blocking layer. It is designed to form layers. Furthermore, the present invention continuously grows a first conductivity type cladding layer, an active layer, a second conductivity type guiding waveguide layer, and a current blocking layer by chemical vapor deposition (MO(, VD) method) using an organic metal. After that, an etching mask is formed on the current blocking layer, and the current blocking layer is selectively etched using this etching mask to form a striped groove. After removing this etching mask, a second striped groove is formed. A periodic etching mask is formed on the conductive optical waveguide layer, and the second conductive optical waveguide layer is etched using this etching mask to form periodic irregularities. After removing this etching mask, MOCVD is performed. In this method, a second conductivity type cladding layer and a second conductivity type contact layer are grown on a second conductivity type optical waveguide layer and a current blocking layer on which periodic irregularities are formed by a method.

(Function) According to the present invention, since the transverse mode control 1nGaAlP semiconductor laser has a built-in diffraction grating, it has strong wavelength selectivity and can oscillate in a single longitudinal mode, and can also change the period of the diffraction grating. By doing so, the oscillation wavelength can also be freely selected. Furthermore, the structure of the laser is very simple and can be produced by only two crystal growths, resulting in high yield and low cost.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
FIG. 1 is a diagram showing a schematic structure of a semiconductor laser according to an embodiment of the present invention. In the figure, 10 is an n-GaAs substrate, 1
1 is n Ino, 5 (GaAl)
P cladding layer, 120.3 0.7 0.5 is non-doped InGaP active layer, 13 is pIn (
GaAl) P optical waveguide 0.5
0.7 0.3 0.5 layer, 14 is current blocking layer, 15
is pIn1), 5(GaAl)
P cladding layer, 17 is 0.3 0.7 0.5 p-GaAs contact layer, 17 is diffraction grating, 18 is n
The electrodes 19 each indicate a p-electrode.

In this laser, n - Ga A s outside the stripe
A current blocking layer 14 is disposed adjacent to the active layer 12;
Since this n-GaAs layer functions as a light absorption layer, a difference in complex refractive index occurs between the stripe portion and the outside of the stripe portion, thereby realizing optical confinement in the horizontal direction. Also, n
- Since the GaAs layer also blocks current, low threshold characteristics can be obtained.

Next, the effect of the built-in diffraction grating will be explained. That is, only the light directed toward the cavity is amplified by the diffraction grating, and when a certain threshold value is reached, laser oscillation occurs. The oscillation wavelength λ at that time is expressed by the following equation.

λx 2ne knee'-" (m=1.2.3-)
Here, neff is the equivalent refractive index, and A is the period of the diffraction grating. Therefore, by changing the period A of the diffraction grating, the oscillation wavelength λ can be changed.

Further, FIG. 2 shows the refractive index n for the A1 composition X. The refractive index of each layer in the example shown in FIG.
The active layer is 3.65, the optical waveguide layer is 3.55, and the cladding layer is 3.4, resulting in an equivalent refractive index of about 3.5. Therefore, in order to make the oscillation wavelength about 6700 A, the period of the diffraction grating is 960 XmA, and from the viewpoint of ease of manufacturing the diffraction grating, the value of m is preferably 2.

Next, a method for manufacturing the semiconductor laser having the above structure will be described.

FIGS. 3(a) to 3(C) are cross-sectional views showing the manufacturing process of the example laser. First, by the MOCVD method at less than atmospheric pressure using metallic Group I organic metals (trimethylindium, trimethylgallium, trimethylaluminum) and Group V hydrides (arsine, phosphine) as raw materials, the material shown in Figure 3(a) was produced. n-G of plane orientation (100) as shown in
aAs substrate 10 (Si doped, 3 x 10I8c+n
-3) 0.8 μm thick n-In (Ga
O, 50, 8 AI) P cladding layer 11 (Si mid-, 70
, 5 p, 4 x 10' cm-3), thickness 0.06 μm
In0.5 Ga P active layer 12, 0.15 μm thick pIn
(GaAl)P optical waveguide layer 0.
5 0.7 0.3 0.513 (Zn doped,
4 x 1017 cm'-3), 0.5 μm thick n
- A GaAs current blocking layer 14 was continuously grown. continue,
As shown in FIG. 3(b), using a photoresist film as a mask, the n-GaAs current blocking layer 14 is etched by chemical etching until the p-leading waveguide layer is exposed.
Striped grooves with a width of 5 μm were formed. Next, after removing this photoresist mask, a diffraction grating having a period of 1920A was formed on the photoresist using a three-beam interference exposure apparatus. Next, using the photoresist as a mask, a diffraction grating is transferred onto the p-optical waveguide layer 13 by chemical etching. Next, by the above MOCVD method,
As shown in FIG. 3(C), p-I n with a thickness of 1 μm
(Ga0.30.5 AI) P cladding layer 15 (Zn doped, 0
．． 7 0.5 4 X 10 '7cm-'') -3μm thick p-Ga
As:I 8 layers 16 (Z'n doped, 5x1018)
grew continuously. After that, p-
An n-type electrode 19 is placed on the cyaAs contact layer 16, and an nG
A laser wafer having the structure shown in FIG. 1 was prepared by depositing an n-type electrode 18 on the lower surface of the aAs substrate.

The thus obtained wafer was folded and the cavity length was 250μ.
When we created a DFB laser of m, the threshold current was 40
mA was obtained, and stable single longitudinal mode oscillation was exhibited up to 10 mW or more. Also, in the manufacturing method, the number of growths is 2.
Since the process is simple and requires only a few steps, DFB lasers with uniform characteristics can be obtained at a high yield.

Next, a second embodiment will be described. FIG. 4 shows its schematic structure. The difference from FIG. 1 is that the InGaP active layer 1
2 and p I n (G a O, 70, 5 Al ) P optical waveguide layer 13 .
, 30,5 n o, 5(G a A 1 ) P via layer 200.3 0.7 0.5 (Zn doped, 4 x 10'cm"). This allows for separation from the active layer. The electron overflow can be further reduced, and a DFB laser with a low threshold value and excellent temperature characteristics can be obtained.

Note that the manufacturing process is the same as the manufacturing process shown in FIG. 3.

As described above, according to this embodiment, a transverse mode control laser that stably oscillates in a single longitudinal mode with a low threshold value can be realized with high yield.

In addition, the present invention also provides the G
In addition to aAs, GaA IAs or In0.5
(GaAl) P(z<w≦1)
1-w w O,5 may be present. Further, in the embodiment, the first conductivity type is n type and the second conductivity type is p type, but it goes without saying that these may be reversed. In addition, various modifications can be made without departing from the gist of the present invention.

Next, other embodiments of the present invention will be described with reference to the drawings. FIG. 5 is a diagram showing a schematic structure of a semiconductor laser device according to an embodiment of the present invention.

In the figure, 10 is an n-GaAs substrate, 1j is nIn (
GaAl) P cladding layer, 0.5
0J O,70,5 12 is non-doped I nGaP active layer, 13 is pIn
(GaAl) P optical waveguide layer, 0
．． 5 0.7 0.3 0.514 is a diffraction grating,
15 is p I n (GaO, 30,5 AI) cladding layer, 16 is n-GaAs0
．． 7 0.5 current blocking layer, 17 a p-GaAs contact layer, 18 a 0 electrode, and 19 a p electrode, respectively. In this laser, an n-GaAS current blocking layer 16 is placed close to the active layer 12 outside the stripe;
Since the layer acts as a light absorption layer, a difference in complex refractive index occurs between the ridge portion and the set of ridge portions, thereby realizing optical confinement in the horizontal direction. Furthermore, since the n-GaAs layer also blocks current, a low threshold characteristic can be obtained.

Next, the effect of the built-in diffraction grating will be explained. In other words, only the light in the direction of the cavity is amplified by the diffraction grating,
Laser oscillation occurs when a certain threshold is reached. The oscillation wavelength λ at that time is expressed by the following equation.

λ = "neff A (m = 1.2.3-) where neff is the equivalent refractive index, and A is the period of the diffraction grating. Therefore, if the period of the diffraction grating is changed, the oscillation wavelength λ
can be changed.

Further, FIG. 6 shows the refractive index n for the A1 composition X. In the example shown in FIG. 5, the refractive index of each layer is 3.65 for the active layer, 3.55 for the leading waveguide layer, or 3.55 for the cladding layer.
4, and the equivalent refractive index is about 3.5. Therefore, in order to make the oscillation wavelength about 6700 A, the period of the diffraction grating is 960×m A, and from the viewpoint of ease of manufacturing the diffraction grating, the value of m is preferably 2. Next, a method for manufacturing the semiconductor laser having the above structure will be described.

FIGS. 7(a) to 7(h) are cross-sectional views showing the manufacturing process of the example laser. First, MOCV was conducted under pressure below atmospheric pressure using metal-based group Ⅰ organic metals (trimethylindium, trimethylgallium, trimethylaluminum) and group Ⅰ hydrides (arsine, phosphine) as raw materials.
By the D method, the plane orientation (100) is obtained as shown in Figure 3 (a).
nGaAs substrate 10 (Si doped, 3×1o18cr
rl-3) with a thickness of 0.8 pm on
(Gao, 30.5 A 1 o, r) o, 5P layer cladding layer 1
1 (Si doped, 4 x 1017 cm-3), thickness 0. O
ffμm InGao, 5P active layer 12, 0.15μm thick pIn (C,a AlO,50,70,3)0.5P optical waveguide layer 13 (Zn
A dope (4×1017 cm-”) was continuously grown. Then, using a three-beam interference exposure apparatus, a diffraction grating having a period of 1920 A was formed on the photoresist as shown in FIG. 3(b). As shown in FIG. 7(C), a diffraction grating is transferred onto the leading waveguide layer by chemical etching using a photoresist as a mask.

Next, as shown in FIG. 7(d), a 0.8 μm thick p I n o,5(Ga
Al ) P cladding layer 15 (ZO, 30
,70,5 n-doped, 4. x 1017 cm'=). Next, as shown in FIG. 7(e), a Si02 film 21 was formed in a stripe shape with a width of 5 μm. Next, Fig. 7 (f
) Using the <5i02 film 21 as a mask, the p-cladding layer 15 was chemically etched until the diffraction grating was exposed, thereby forming a striped ridge with a width of 3 μm.

Next, by low-pressure MOCVD using trimethylgallium and arsine as raw materials, <n −
Ga As current blocking layer 1B (Si doped, 5×10
18 cm-3) was grown to a thickness of 0.5 μm. Then, S
After removing the i02 film 21, as shown in FIG. 3(h),
A p-GaAs contact layer 17 (ZnF-), 5 x 1018 am'') is formed on the entire surface by MOCVD method.
was grown to a thickness of 3 μm. Thereafter, a p-type electrode is formed on the contact layer 17 and an n-type electrode is formed on the lower surface of the substrate 10 by a normal electrode process.
By depositing electrodes, a laser wafer having the structure shown in FIG. 5 was prepared.

The thus obtained evaporator was cleaved and the resonator length was 250μ.
When we created a DFB laser of m, the threshold current was 40
mA was obtained, and stable single longitudinal mode oscillation was exhibited up to 10 mW or more.

Next, a second embodiment will be described. FIG. 8 shows its schematic structure, and the differences from FIG. 5 are the InGaP active layer 12 and p I n (G a o , 70.5 AI). pIn between JO,5P optical waveguide layer 13
(GaAl)P barrier layer 0.5
0J O,70,522 (Zn doped,
4 x 10 'cm"-3). This makes it possible to further reduce the overflow of electrons from the active layer, making it possible to obtain a semiconductor laser with a low threshold value and excellent temperature characteristics. The manufacturing process is the same as the manufacturing process shown in FIG.

As described above, according to this embodiment, it is possible to realize a transverse mode controlled laser that stably oscillates in a single longitudinal mode.

In addition, the present invention uses GaA as described in the embodiment as the current blocking layer.
In addition to s, GaA IAs or In (G
a A1 ) P(z<w≦1)0.5
1-w w O,5 may be sufficient. moreover,
In the embodiment, the first conductivity type is n type and the second conductivity type is p type, but it goes without saying that these may be reversed. In addition, various modifications can be made without departing from the gist of the present invention.

As described in detail above, according to the present invention, since the diffraction grating is built-in, it is possible to realize a transverse mode controlled laser that stably oscillates in a single longitudinal mode.

[Effects of the Invention] As described in detail above, according to the present invention, since the diffraction grating is incorporated, it is possible to realize a transverse mode controlled laser that stably oscillates in a single longitudinal mode.

Furthermore, since the manufacturing process is simple and requires only two growths, DFB lasers with uniform characteristics can be obtained at a high yield and at a low price.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a perspective view showing the first embodiment of the present invention, FIG. 2 is a diagram showing the relationship between A1 composition X and refractive index n of InGaAIP, and FIG. 3 is a diagram showing the invention FIG. 4 to FIG. 8 are diagrams for explaining other embodiments, and FIG. 9 is a diagram showing a conventional example. 10---n-GaAs substrate, 11 ・=
n I n 0.5 (Ga Al )
P cladding layer, 12 ・=-0, 30, 70, 5 Non-doped In Ga P active layer, 13...
pO150°5 In (Ga Al O, 50, 70, 3) 0.5 P optical waveguide layer, 14-n
-G a As current blocking layer, 15 ・p -In
(GaAlO, 50, 80, 7)
0.5 P-Cl 91 layer 116... p-GaAs contact layer, 17... diffraction grating, 18... n electrode, 19
...p electrode, 2o...p-In (Ga
Al ) P barrier layer.

Claims (5)

[Claims] (1) First conductivity type In_0 on the first conductivity type GaAs substrate
＿． _5(Ga_1_-_zAl_z)_0_. ＿5P
Cladding layer, In_0_. _5(Ga_1_-_xAl
＿x）＿０＿． _5P active layer, second conductivity type In_0_.
_5(Ga_1_-_yAl_y)_0_. A double heterostructure made of a _5P optical waveguide layer, a current blocking layer formed on the surface of the double heterostructure excluding the stripe part, and the second conductivity type In_0_. ＿５(
Ga_1_−_yAl_y)_0_. A second conductive type In_0_. _5 (Ga_1_-__zAl_z)_0
＿． _5P cladding layer (0≦x<y<z≦1) and second
1. A semiconductor laser device comprising a conductive contact layer. (2) Said In_0_. _5(Ga_1_-_xAl_
x) ＿0＿. _5P active layer and second conductivity type In_0_.
_5(Ga_1_-_yAl_y)_0_. _5P optical waveguide layer and the second conductivity type In_0_. _5(Ga_1
____zAl_z)_0_. 2. The semiconductor laser device according to claim 1, further comprising a _5P barrier layer. (3) First conductivity type In_0 on the first conductivity type GaAs substrate
＿． _5(Ga_1_-_zAl_z)_0_. ＿5P
Cladding layer, In_0_. _5(Ga_1_-_xAl
＿x）＿０＿． _5P active layer, second conductivity type In_0_.
_5(Ga_1_-_yAl_y)_0_. _2nd conductivity type I with 5P optical waveguide layer and striped ridge
n_0_. _5(Ga_1_-_zAl_z)_0_.
_5P cladding layer (0≦x<y<z≦1), provided with periodic irregularities between the second conductivity type optical waveguide layer and the second conductivity type cladding layer, and formed on the GaAs substrate. a current blocking layer formed on the double heterostructure at least in a region outside the ridge portion of the second conductivity type cladding layer; and a current blocking layer formed on the second conductivity type cladding layer and the current blocking layer. 1. A semiconductor laser device comprising: a second conductivity type contact layer formed thereon. (4) First conductivity type In_0_. ＿5(G
a_1_−_zAl_z)_0_. _5P cladding layer,
In_0_. _5(Ga_1_-_xAl_x)_0_
．． _5P active layer, second conductivity type In_0_. _5(Ga_
1_-_yAl_y)_0_. _A step of successively growing a 5P optical waveguide layer and a current blocking layer, a step of forming an etching mask on the current blocking layer, and a step of forming the current blocking layer into the second conductivity type optical waveguide using the etching mask. forming stripe-shaped grooves in the current blocking layer by selectively etching until the surface of the layer is exposed; removing the etching mask; a step of etching the second conductivity type optical waveguide layer using the etching mask to form periodic irregularities; a step of removing the etching mask; By the chemical vapor deposition method used, second conductivity type In_0_. _5(Ga_
1_-_zAl_z)_0_. A method for manufacturing a semiconductor laser device, comprising the step of successively growing a _5P cladding layer and a second conductivity type contact layer. (5) First conductivity type In_0_. ＿5(G
a_1_−_zAl_z)_0_. _5P cladding layer,
In_0_. _5(Ga_1_-_xAl_x)_0_
．． _5P active layer, second conductivity type In_0_. _5(Ga_
1_-_yAl_y)_0_. _A step of continuously growing a 5P optical waveguide layer, a step of forming a periodic etching mask on the second conductivity type optical waveguide layer, and a step of forming the second conductivity type optical waveguide layer using the etching mask. A step of etching to form periodic asperities, a step of removing the etching mask, and then a chemical vapor deposition method using an organic metal is performed on the second conductive type optical waveguide layer in which the periodic asperities are formed. to the second conductivity type In_0_. ＿５(
Ga_1_−_yAl_y)_0_. _A step of growing and forming a 5P cladding layer, a step of forming an etching mask on the second conductivity type cladding layer, and selectively etching the second conductivity type cladding layer halfway through using the etching mask to remove the cladding layer. forming a striped ridge in the layer, and then growing a current blocking layer in a region outside the striped ridge of the second conductivity type cladding layer by chemical vapor deposition using an organic metal. a step of removing the etching mask; and a step of growing a second conductivity type contact layer on the second conductivity type cladding layer and the current blocking layer by a chemical vapor deposition method using an organic metal. A method of manufacturing a semiconductor laser device, comprising: