JPH0823139A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser on a p-InP substrate which operates with low threshold value and at high efficiency. CONSTITUTION:Relating to a semiconductor laser of double hetero structure (DH structure) which, on a zinc(Zn) doping p-type InP (p-InP) substrate 11, includes a p-InP clad layer, active layer, n-type InP (n-InP) clad layer, a p- InGaAs layer 11 or p-InP/p-InGaAs multi-layer film is inserted between a p-InP substrate 10 and p-InP clad layer 12, so that, diffusion of Zn from the p-InP substrate 10 to an InGaAsP active layer 13 is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser,
In particular, it relates to a semiconductor laser which is a main constituent element of an optical communication system.

[0002]

2. Description of the Related Art With the progress of optical communication technology, its applicable fields are rapidly expanding from backbone transmission systems to subscriber systems, LANs, data links, and other systems. Since semiconductor lasers used in these fields are used in various environments and in large amounts, they are required to have excellent environmental resistance performance and low cost, and active research and development are being carried out. Among them, a semiconductor laser array on a p-type InP substrate that can be independently driven as a light source for optical wiring in a computer or an exchange is receiving attention (for example, Oka et al. Technical Report OQE 92-168).
1993).

[0003]

However, when the laser structure shown in FIG. 3 is grown on the p-InP substrate heavily doped with Zn, that is, the p-InP substrate (1
0) on the p-InP clad layer (12), InGaA
After growing the sP active layer (13) and the n-InP clad layer (14), a mesa stripe is formed by wet etching using stripe-shaped SiO ₂ as a mask, and the p-InP buried layer (17) is left with the mask. n-InP current blocking layer (18), p-InP current blocking layer (19)
And then etching the mask to remove n-InP
Buried layer (20), n ⁺ -InGaAs contact layer (2
1) is grown, and n-side electrode (22) and p-side electrode (23)
In the case of forming a p-InP substrate (10), Zn of
If the activation rate is low, Zn diffuses into the indium-gallium-arsenic-phosphorus (InGaAsP) active layer (13), which causes deterioration of laser characteristics such as a decrease in slope efficiency and an increase in internal loss ( For example, Proceedings of the 53rd Japan Society of Applied Physics (18p-ZE-5) by Mizuochi et al.
992). An object of the present invention is to solve this problem and to provide a highly efficient semiconductor laser having a low threshold value by suppressing Zn diffusion from the substrate.

[0004]

SUMMARY OF THE INVENTION The present invention is a p-type indium phosphorus (p-I) using zinc (Zn) as a dopant.
In a double hetero structure (DH structure) semiconductor laser having a p-InP clad layer, an active layer, and an n-type InP (n-InP) clad layer on a (nP) substrate, p-InP
A semiconductor laser is characterized in that a p-type indium gallium arsenide (p-InGaAs) layer is inserted between a substrate and a p-InP clad layer. Further, the present invention provides a p-type indium gallium arsenide (p-type) which is inserted between the p-InP substrate and the p-InP clad layer of the semiconductor laser.
-InGaAs) layer instead of p-InP / p-InGa
The semiconductor laser is characterized in that a multilayer film of As is inserted. In addition, the present invention provides the above semiconductor laser, wherein p-type indium gallium arsenide (p-InGaA) is used.
The s) layer is a p-type indium phosphide (p) having a (100) plane.
-InP) Zn formed on the substrate using MOVPE
Doping p-type indium gallium arsenide (p-In
GaAs) layer.

[0005]

In FIG. 4, the growth temperature is 625 ° C., the growth pressure is 150 Torr, and the molar ratio of the Group 5 raw material and the Group 3 raw material of the periodic table (group 5/3 group ratio) is measured by using metal organic vapor phase epitaxy (MOVPE).
100, growth rate 1 μm / h, Zn concentration 5 × 10 ¹⁸ cm ⁻³
In lattice-matched to InP on p-InP substrate for 3 hours
InGaA of Zn diffusion rate when GaAsP is grown
The sP composition dependence is shown. As is clear from this FIG.
The Zn diffusion rate decreases from nP to InGaAs, and is about 1/3 of InP in InGaAs.
Therefore, as in the present invention, in a semiconductor laser having a DH structure including a p-InP clad layer, an active layer, and an n-InP clad layer on a p-InP substrate using Zn as a dopant, a p-InP substrate and a p-InP substrate are used. By inserting the p-InGaAs layer between the -InP clad layers, diffusion from the substrate can be suppressed, and a highly efficient semiconductor laser with a low threshold value can be realized. In addition, p-InP
Using a / p-InGaAs multilayer film, diffusion from the substrate can be suppressed, and a highly efficient semiconductor laser with a low threshold value can be realized.

[0006]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the present invention. First, (100)
On a Zn-doped p-InP substrate (10) having a surface,
A Zn-doped p-InGaAs layer (p = 7 × 10 ¹⁷ cm ⁻³ ) (11) having a thickness of 0.3 μm and Z was formed by using MOVPE.
n-doped p-InP clad layer (p = 7 × 10 ¹⁷ cm
^-3 ) (12) having a thickness of 2.5 μm and an InGaAsP active layer (13) having a bandgap with an emission wavelength of 1.3 μm
With a thickness of 0.15 μm and silicon (Si) doping n−
An InP clad layer (n = 1 × 10 ¹⁸ cm ⁻³ ) (14) having a thickness of 0.3 μm and an InGaAs layer having a thickness of 0.1 μm are continuously epitaxially grown.

Next, by the CVD technique and the technique of photography, the thickness is about 2000 A and the width is 3 in the <011> direction.
A SiO ₂ stripe-shaped mask of μm is formed at intervals of 300 μm. Then, InGaAs is chemically etched.
The layer, the n-InP cladding layer (14), the InGaAsP active layer (13), and the p-InP cladding layer (12) are etched so that the mesa stripe height is 2.5 μm. Furthermore, while leaving the SiO ₂ stripe mask,
A p-InP buried layer (p = 7 ×) is formed in the recessed portion of the mesa stripe.
10 ¹⁷ cm ⁻³ ) (17) with a thickness of 0.2 μm, n-InP current blocking layer (n = 1 × 10 ¹⁸ cm ⁻³ ) (18) with a thickness of 1
μm, p-InP current blocking layer (p = 7 × 10 ¹⁷ c
m ^-3 ) (19) having a thickness of 1 μm is continuously selectively epitaxially grown using MOVPE.

The SiO ₂ striped mask is removed with ammonium fluoride and then the InGaAs layer is removed. After that, an n-InP buried layer (n = 1 × 10 ¹⁸ cm ⁻³ )
(20) has a thickness of 2 μm, n ⁺ -InGaAs contact layer (n = 1 × 10 ¹⁹ cm ⁻³ ) (21) has a thickness of 0.3 μm,
Each is continuously grown using MOVPE. After that, polishing is performed until the total thickness becomes about 120 μm, and n
N-side electrode (22) on the p-type semiconductor side, P on the p-type semiconductor substrate side
The side electrodes (23) are respectively formed by a vacuum vapor deposition method, annealed, and then cleaved and separated into individual semiconductor lasers, and the whole processing is completed, and the semiconductor laser shown in FIG. 1 is completed.

When this laser was evaluated with a cavity length of 300 μm, the threshold current was 3 mA on average and the slope efficiency was 0.35 W / A on average. This result is improved as compared with the result by the conventional semiconductor laser shown in FIG. 3, and it was confirmed that the device characteristics are improved by using the present invention.

FIG. 2 shows the result of analyzing the Zn concentration profile of the semiconductor laser of the present invention shown in FIG. 1 and the conventional semiconductor laser shown in FIG. 3 by secondary ion mass spectrometry (SIMS). In FIG. 2, the vertical axis represents Zn concentration (cm ⁻³ ), the horizontal axis represents the distance from the surface (μm), and the horizontal axis represents the n-InP clad layer, InGaAsP active layer, p-InP clad layer, And a p-InGaAs layer,
The respective layers of the p-InP substrate are shown. In the case of a conventional semiconductor laser, p-In shown by a dotted line
Zn from the substrate is InGaA as if there were no GaAs layer.
In the semiconductor laser according to the present invention, the p-InGaA shown by the solid line is diffused while the sP active layer (13) is diffused.
As with the s layer, Zn is used in the p-InGaAs layer (11).
You can see that the diffusion has been stopped. As described above, by using the device structure according to the present invention, a low threshold and highly efficient laser can be realized.

[0011]

As described above, when the semiconductor laser structure of the present invention is used, Zn diffusion from the substrate is p-InG.
Since it is blocked by the aAs layer and does not reach the InGaAsP active layer, it has the effect of realizing a highly efficient semiconductor laser with a low threshold value. That is, when a DH structure including a p-InP clad layer, an active layer, and an n-InP clad layer is grown on a p-type p-type InP substrate, unactivated Zn diffuses from the substrate and affects the active layer. Influences and deteriorates the laser characteristics. On the other hand, the diffusion constant of Zn between the p-type InP substrate and the p-InP clad layer is InP.
Smaller InGaAs layer or InP / InGaA
By inserting the s multilayer film, diffusion of Zn from the substrate can be suppressed, and good laser characteristics can be obtained even on the p substrate.

[Brief description of drawings]

FIG. 1 is a sectional structural view of a semiconductor laser showing an embodiment of the present invention.

FIG. 2 is a diagram showing the results of measuring the Zn concentration in the depth direction from the surface of the semiconductor laser of the present invention and the conventional semiconductor laser by SIMS analysis.

FIG. 3 is a sectional structural view of a conventional semiconductor laser.

FIG. 4 is a diagram showing the Zn diffusion length dependence of the InGaAsP composition that is lattice-matched to InP.

[Explanation of symbols]

10 p-InP substrate 11 p-InGaAs layer 12 p-InP clad layer 13 InGaAsP active layer 14 n-InP clad layer 17 p-InP buried layer 18 n-InP current block layer 19 p-InP current block layer 20 n- InP buried layer 21 n ⁺ -InGaAs contact layer 22 n-side electrode 23 p-side electrode

Claims (2)

[Claims] 1. A p-In on a p-type Indium-Phosphorus (p-InP) substrate using zinc (Zn) as a dopant.
In a double hetero structure (DH structure) semiconductor laser having a P clad layer, an active layer, and an n-type InP (n-InP) clad layer, a p-type indium gallium Arsenic (p-InG
A semiconductor laser having an aAs) layer inserted therein. 2. A p-InP substrate according to claim 1 and a p-InP substrate.
Instead of a p-type indium gallium arsenide (p-InGaAs) layer inserted between the InP clad layers, p-In
A semiconductor laser comprising a P / p-InGaAs multilayer film.