JPS6083388A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To prevent leakage current of the photo absorption layers due to an optically pumped minority carrier by a method wherein layers, which perform photo absorption, and layers, which perform current constriction, are separated from each other. CONSTITUTION:An n type semiconductor layer 2; a semiconductor layer 3 having a smaller forbidden band width than that of the layer 2; a p type semiconductor layer 4 having a larger forbidden band width than that of the layer 3; semiconductor layers 8-10, each having a striped groove; and a p type semiconductor layer 6 having a larger forbidden band width than that of the layer 3 are provided on an n type substrate 1. The layer 8 is a p type layer and has a smaller forbidden band width than that of the layer 3. The layer 9 has a p type and the layer 10 has an n type. The layers 9 and 10 have a larger forbidden band width than that of the layer 3. The layer 3 and the layer 8 substantially absorb respectively lights, which are emitted from the laser active layers and the active layers, and both make a control of transverse mode performance. As a result, leakage currnent of the photo absorption layers can be prevented by a p-n junction, which is formed by the layers 9 and 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to the structure of a semiconductor laser device, and in particular to the structure of a single mode laser with stable transverse mode.

[Background of the invention]

A conventional self-aligned semiconductor laser has n(GaAt)A on an n-type GaAs substrate 1, as shown in the cross-sectional view of FIG.
s cladding layer 2, undoped (GiaAt)As active layer 3% p(GaAt)As cladding layer 4. n-Ga
As, the entire light absorption layer 5 is formed, and a part of the light absorption layer is removed in the form of stripes by etching, and p-(GaAt)A is formed.
It is filled with s6 and p-GaAs7, and has both IT flow constriction and waveguide formation due to the light absorption layer, but the threshold value increases due to leakage current due to minority carriers generated by light absorption. There was a problem.

[Purpose of the invention]

Another object of the present invention is to perform stable laser oscillation in transverse mode, to be able to produce it in a self-aligned manner, and in particular, to form an active layer entirely flat.
chemical vapor deposition
) to provide a semiconductor laser structure suitable for production.

[Summary of the invention]

This has been a problem with conventional self-aligned semiconductor lasers. In order to prevent current leakage in the light absorption layer due to photoexcited minority carriers, the layer that performs all light absorption and the layer that performs current confinement are separated. This completely solves the problem of increasing the threshold voltage due to leakage current, which was a problem in conventional P1 structures of this type.

The specific configuration is as follows.

A first semiconductor layer having the same conductivity type as the substrate, a second semiconductor layer having a forbidden band width smaller than that of the first semiconductor layer, and a first conductivity layer on a semiconductor substrate having a first conductivity type. a third semiconductor layer having a second conductivity type opposite to the conductivity type and having a forbidden band width larger than the forbidden band width of the second semiconductor layer; The fourth groove has a groove shaped like this. the fourth semiconductor layer comprises fifth and sixth semiconductor layers, a seventh semiconductor layer having a second conductivity type and a forbidden band width larger than at least the second semiconductor layer, and at least gold; The fifth semiconductor layer has a second conductivity type and has a smaller forbidden band width than the second semiconductor layer, the fifth semiconductor layer has a second conductivity, and the sixth semiconductor layer has a first conductivity. It is characterized by having a mold. Furthermore, the fifth and sixth semiconductor layers are usually provided to have a forbidden band width υ larger than that of the second semiconductor layer.

Also, more practically, a cap layer, which is used in many semiconductor lasers, is provided on the sixth semiconductor layer.

The second semiconductor layer is an active layer of the laser, the fourth semiconductor layer is a layer that substantially absorbs the optical sound emitted by the active layer, and controls the transverse mode; The p-n junction formed by the semiconductor layer prevents current leakage.

The key point of the present invention is to provide the layer for light absorption and the layer for current confinement separately in this way.

The layer for current confinement may be configured as a larger number of layers.

[Embodiments of the invention]

An embodiment of the present invention will be explained below with reference to FIG. n-
n on a GaAs substrate (1) by the well-known MOCVD method.
-G a6. s s ALo, 4s A s clad j group 2) (8e v-pu, n=5X1017crn-
”, 1 μm), non-doped Gao, 5aAto, +<
As active layer (3) (0.06-0.1 μm), p
Q a6. BB kL6.45 As clad; group 4)
(Zn-doped, p = 3 x 1017cm-3
, 0.4 μm) p-Ga, As light absorption layer (8) (
Zn-doped p = 3 x 10"an-",
0.5 am) ri Gao, ss Ato, 4s
As layer (9) (Z fl doped p=3 x 10”
cm-30,2μm) n-Gao, ss At
After crystal-growing the O,46As current blocking layer (10) (S e doped n = 5X10I7'tyn-" 0.3 μm), the layers above the light absorption layer are formed into stripes using normal photolithography technology. Etching was performed on the structure formed in the above manner by MOCVD again.
bp-(Flo, ss Ato, 4s people 5 layers (6)
(Zn-doped p=3×10"cm-" 1 μm) and a p-GaAS cap layer 7 having a conductivity type opposite to that of the substrate (
Zn-doped p=IX1σ80-30,5μm) was formed, Au/Cri was used as the p-side electrode (11), and Au/Cri was used as the n-side electrode (11).
12], Au@Ge.Ni/Cr/Au was vacuum deposited. Finally, the crystal was cleaved to a cavity length of 300 μm to form a resonator and a laser chip. According to the semiconductor laser structure of this example, the current confinement and light absorption functions performed by the light absorption layer in the conventional self-aligned semiconductor laser are now performed separately by the light absorption layer and the current blocking layer. Therefore, leakage current due to minority carriers generated in the light absorption layer, which was a problem in the conventional structure, does not occur, and the threshold current becomes small. The semiconductor laser of this example has a threshold current of 20 rnA and a temperature continuous oscillation at a wavelength of 780 nm, and a lifetime test of 5 products with a constant output of 500 nm at 70C.
No significant device deterioration was observed even after continuous operation for more than 0 hours.

Although the above-mentioned example is an example of an n-conductivity type substrate, a p-conductivity type substrate may also be used, and it goes without saying that in this case, the semiconductor layers 94 are of opposite conductivity type. Furthermore, GaAs-
The structure of the present invention can be realized not only in QaAAAs-based semiconductor lasers but also in semiconductor lasers using compound semiconductors.

〔Effect of the invention〕

According to the present invention, since the active layer' can be formed flat, M
In addition to eliminating the reduction in reliability due to defects that occur at the corners when growing on grooved substrates, which was a problem with OCVD lasers, the optical Since there is no leakage current due to the photo-silisk effect caused by minority carriers generated in the absorption layer, the threshold value has also been lowered.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a self-aligned semiconductor laser with a conventional structure.
FIG. 2 shows a cross-sectional view of the semiconductor laser according to the present invention, viewed from the direction in which laser light travels. 1--n QaAs substrate, 2--n (GaAt
)As cladding layer, 3...active layer, 4...p(Ga
A, lAs cladding layer, 5...n light absorption layer, 6-1)
(GaAtlAs layer, 7...pQaAs cap layer, 8...I) GaAs, light absorption layer, 9-p(
GaAA) As layer, 10-...n (GaAA)As
layer.

Claims (1)

[Claims] 1. On a semiconductor substrate having a first conductivity type metal, a first semiconductor layer having the same conductivity type as the substrate, and a second semiconductor layer having a smaller forbidden band width than the first semiconductor layer. a third semiconductor layer having a second conductivity type opposite to the first conductivity type and having a forbidden band width larger than the forbidden band width of the second semiconductor layer; A fourth semiconductor layer having stripe-shaped grooves on the semiconductor layer No.3. The 40th semiconductor layer includes at least a fifth and a sixth semiconductor layer, and a seventh semiconductor layer having a second conductivity type and having a larger forbidden band width than at least the second semiconductor layer; The layer has a conductivity type @2 and has a forbidden band width smaller than that of the second semiconductor layer, the fifth semiconductor layer has a second conductivity type, and the sixth semicircular body 1171 has A semiconductor laser device having a first conductivity type. 2. The semiconductor laser device according to claim 1, wherein the fifth and sixth semiconductor layers have a narrower band gap than the second semiconductor layer.