JPS62186582A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain an element having uniform characteristics with excellent reproducibility, by making the carrier density of the both end-layers of a multilayer-type current blocking layer formed on a clad layer ununiform in the direction of layer thickness, and providing a stripe-type window at a specified position of the current blocking layer. CONSTITUTION:On an N-type GaAs substrate 1 the following layers are grown in order; a buffer layer 3, a clad layer 3, an active layer 4, a clad layer 5 and a multilayer-type current blocking layer 6 composed of a GaAs buffer layer 12 and an N-type GaAs layer 13. In this process, the carrier density of the N-type GaAs layer is made ununiform in the direction of layer thickness. The current blocking layer 6 is subjected to etching, and a stripe-type window W is formed, on which a clad layer 8, a contact layer 9 and an electrode 10 are formed. An electrode 11 is formed on the opposite surface of the substrate 1. Thereby, a laser device can be manufactured with excellent reproducibility, which has uniform characteristics and oscillates in a fundamental transversal mode with a small current.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser device, which has been rapidly used as a light source for various electronic devices and optical devices in recent years, and is in increasing demand.

(Prior Art) Important performances required of semiconductor lasers as coherent light sources for electronic and optical equipment include low current operation and fundamental transverse mode oscillation. In order to achieve these performances, it is necessary to suppress and confine the current so as to concentrate it near the active region where the laser light propagates. A semiconductor laser with such a structure built inside is usually called an internal stripe type laser. (For example, Compound Semiconductor Devices (If) edited by Tetsuji Imai et al.
.

214-p, 215) Hereinafter, the conventional internal stripe type laser as described above will be explained with reference to the drawings.

In FIG. 3, 1 is an n-type GaAs substrate, 2 is an n-type GaAs substrate, and 2 is an n-type GaAs substrate.
As buffer layer, 3 is n-type AtGaAs cladding layer, 4
5 is an AtGaAs active layer, 5 is a p-type AtGaAs cladding layer, 14 is an n-type GaAs current blocking layer, and 8 is a p-type AtGaAs layer.
Ag cladding layer, 9 p-type GaAs contact layer, 10
is a p-side ohmic electrode, and 11 is an n-side ohmic electrode.

The manufacturing method and operation of the internal stripe type laser constructed as described above will be briefly described below.

Internal stripe lasers are formed in two crystal growth steps. Here, the MOCVD method is used for the crystal growth process. As the first crystal growth, n-type GaA is grown on the n-type substrate 1.
s buffer layer 2, n-type A7GaAs cladding layer 3, At
Ga, As active layer 4, p-type A7GaAs cladding layer 5,
An n-type GaAs current blocking layer 14 is sequentially grown.

The growth conditions were that the growth temperature was 800°C, and the molar ratio (I1 ratio) of the group II element to the group II element was 20. Growth rate is 5μm
/It's time. Next, the grown n-type GaAs layer is
Stripes with a width of 5 μm at a pitch of 0 μm are formed using 7 photoresist films. At this time, the stripe is n-type GaA
parallel to the (Oli) direction of the s-substrate. Selective n-type GaAs current blocking layer 1 by chemical etching
4 by the internal stripe width W, and the n-type AtG
The aAs cladding layer 5 is exposed. Furthermore, a second crystal growth is performed on the surface on which the internal stripes are formed by MOCVD.

That is, an n-type AtGaAs cladding layer 8 and a p-type GaAs contact layer 9 are sequentially grown. (2) side and n side (C are respectively formed on ohmic electrodes 10 F 11-, and the device is completed.

When voltages of (+) and n(lll electrode 11tu-1 are applied to the p-side electrode 10, only the p-n junction at the interface between the n-type aAs current blocking layer 14 and the p-type A/!GaAs cladding layer 5 is applied in the power direction, and the other voltage is applied in the forward direction, so that the injected current flows only from the internal stripe width W.
Current concentrates in the active layer 4 directly below it, and as a result, low current operation basic tank mode oscillation is realized.

(Problems to be Solved by the Invention) However, as mentioned above, when epitaxial growth is performed at a crystal growth temperature of 800C or higher, n-type AtGaAs
Zn in the p-type layer 5.8 in the cladding layer 5.8 diffuses into the n-type layer aAs current barrier II layer 14, and a part of the n-type layer aAs current barrier layer 11- and layer 14 are heavily concentrated with Zn. Compensated metamorphic strata may be formed. 1/ko, n-type GaA
B The thickness of the Tt current blocking layer 14 and the resulting current limit 1) cause local variations in effectiveness, resulting in, for example, variations in the operating current value between the valley and the end within the same web. Increase the total variation.

In view of the above problems, the present invention provides n-type GaA in the wafer plane.
s suppressing variations in the layer thickness and current blocking effect of the current blocking layer, and suppressing variations in the layer thickness and current blocking effect of the n-type GaAs current blocking layer and the p-type AtGa sandwiching it.
A buffer layer with non-uniform carrier concentration in the layer thickness direction is inserted between the As cladding layers, resulting in a structure that suppresses variations in operating current, etc. between each laser element within the same wafer, making it easier to obtain uniform elements. The present invention provides a semiconductor laser device having the following features.

(Means for Solving the Problems) In order to solve the problems mentioned above, the semiconductor laser device of the present invention has a double heterostructure including an active layer on a substrate and a cladding layer on the active layer. A current blocking layer is formed on the cladding layer, the current blocking layer comprising at least one layer having a conductivity type opposite to that of the cladding layer, and having striped windows at predetermined positions. This is because the carrier concentration is non-uniform in the layer thickness direction within the layers at both ends of the multilayer current blocking layer.

(Function) With this configuration, it is possible to realize a semiconductor device with good uniformity within the wafer plane, an internal stripe structure, a low l-threshold, low current operation, and fundamental transverse mode oscillation. can.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a cross section of a semiconductor laser device according to an embodiment of the present invention. In Figure 1, 1 is n-type GaA
s substrate, 2 is n-type GaAs buffer layer, 3 is n-type AtG
aAs cladding layer, 4 is A7GaA 8 active layer, 5 is p
type AtGaAl1 cladding layer, 6 is a multilayer current blocking layer,
8 is a p-type AtGaAs cladding layer, 9 is a p-type GaAs contact layer, 10 is a p-side ohmic electrode, 11 is an n-side ohmic electrode, 12t is a GaAs buffer layer, and 13 is an n-type GaAs layer.

FIG. 2 is a diagram showing the manufacturing process of the semiconductor laser device of this example, in which 5 is a p-type A7GaAs cladding layer, 6 is a multilayer current blocking layer, and 7 is a fumetresist film.

Next, a method for manufacturing the semiconductor laser device having the above configuration will be explained.

Here, an n-type GaAs substrate is used as the substrate.

First, on this n-type GaAs substrate 1, a pn-type GaAs buffer layer 2 of 0.5 fi'' was formed by metal organic vapor phase epitaxial growth (MOCVD), and an n-type AtxGa 1-
xA s cladding layer 3 of 1.2 μm SAt, Ga1
-, As active layer 4 (0≦y<X) by 0.1 μffZ s
p-type AtXGa, -xAs cladding layer 5 with a thickness of 0.3μ
m, and a GaAs buffer layer 1 with a thickness of 0.211 m.
2. 0.5 μm thick n-type GaAs layer 13 (carrier concentration 5×10 crn) and 0.2 pm thick GaAs layer 13
A multilayer current blocking layer 6 consisting of a buffer layer 12 is sequentially grown. The growth conditions were as follows: growth temperature 800° C., supply molar ratio of group Ⅰ elements to group ① elements was 50, growth rate was 5 μm, and total gas flow rate was 10 μm.

Next, as shown in FIG.
11> Parallel to the direction, 50 μm wide at a pitch of 250 μm
7. Stripes of the photoresist film 7 are formed on the multilayer current blocking layer 6. Next, using the photoresist 7 as a mask, a part of the multilayer current blocking layer 6 is etched in the depth direction by chemical etching until the surface of the p-type AtGaAa cladding layer 5 is exposed, thereby forming a window.

After cleaning the surface, p-type kl, G
a 1-2A s cladding layer 8 with a thickness of 1.2 μm,
The p-type GaAs contact layer 9 is made of M with a thickness of 1.5 μm.
It is grown by OCVD method. The growth conditions are the same as those for the first crystal growth.

An n-side ohmic electrode 11 is formed of AuGeNi on the n-type GaAs substrate 1, and an Au layer is formed on the p-type GaAa contact layer 9.
A p-side half-mick electrode 10 is formed of Zn, and the device is completed.

When the fabricated semiconductor laser device is mounted and operated by passing a current, the current is constricted to the stripe width of W shown in FIG. Expressing an example of typical laser characteristics within a wafer in terms of a threshold current value, a low threshold current value of 35 mA was obtained at w=2 μm, and the oscillation was stable fundamental transverse mode oscillation.

By the way, during the epitaxial growth by MOCVD twice, Zn in the p-type AZxGa1-xAs cladding layer 5 and the p-type At2Ga1-2A8 cladding layer 8 was
It diffuses into the multilayer current blocking layer 6. Ga in the multilayer current blocking layer 6 in the epitaxial layer thickness direction is measured by SIMS.
As a result of examining the Zn concentration distribution in the As buffer layer 12.12, it was found that the carrier concentration of the p-type AtGaAs cladding layers 5 and 8 varied non-uniformly at lX10 crn t. On the other hand, in the conventional internal striation structure shown in FIG. 3, many of them oscillated at a relatively high threshold current value of about 50 volts at w=2 μm.

Further, the dispersion of threshold current values among 30 elements was approximately 172 in the device of the present invention compared to the conventional device.

The reason is not clear, but in the conventional structure, the cladding layer 5
, 8 diffuses into the n-type current blocking layer at a high concentration, and a metamorphosed layer is formed at the interface between the cladding layer and the n-type current blocking layer before diffusion.

Furthermore, in the case of the present invention, the band of the n-type layer is tilted due to the non-uniform concentration, and the photo-generated electrons stay near the junction for a longer time than in the case of uniform concentration, increasing the probability of recombination. As a result, it is thought that the current blocking effect becomes less likely to lapse due to generation of photovoltaic force.

Note that in this example, GaAs s-based, GaAtA a
Although the description has been made regarding a semiconductor laser based on InP, the present invention can be similarly applied to a semiconductor laser device made of a compound semiconductor including an InP-based or other multi-component mixed crystal system. Furthermore, an AtGaAa layer may be used as the buffer layer instead of the GaAs buffer layer.

(Effects of the Invention) As explained above, according to the present invention, it is possible to easily form an internal stripe structure with good reproducibility, and as a result, a high-performance semiconductor laser that oscillates in the fundamental transverse mode at a severe current value can be obtained. The device can be provided, and its practical effects are significant.

2 are diagrams showing the manufacturing process of the same embodiment, and FIG. 3 is a sectional view of a conventional semiconductor laser device.

1... n-type GaAs substrate, 2... n-type GaAs buffer layer, 3- n-type AtGaAa cladding layer, 4- A
tGaAg active layer, 5...p-type Aj! GaAs cladding layer, 6... multilayer current blocking layer, 7... photoresist film, 8... p-type A/, GaAs cladding layer, 9...
...p-type GaAs contact layer, 10...p-side ohmic electrode, 11...n-side ohmic electrode, 12 =-
GaAs buffer layer, 1:l-n type GaAs layer, w"'
Internal stripe width.

Figure 1 1-n type GaAskk 2 N-type layer OAS pap y1 9　9　9riGaAs　Conclude W, Inner scale strut 4 ゛shima

Claims (1)

[Claims] A multilayer thin film formed on a substrate and consisting of a double heterostructure including an active layer and having a cladding layer on the active layer; and a layer formed on the cladding layer and having a conductivity type opposite to that of the cladding layer. The current blocking layer has a stripe-like window at a predetermined position, and the carrier concentration is nonuniform in the layer thickness direction in the layers at both ends of the multilayer current blocking layer. A semiconductor laser device characterized by: