JPH08288586A - 2mum band semiconductor laser - Google Patents

Abstract

PURPOSE: To obtain a semiconductor laser of specified band having low oscillation threshold value and operating current and excellent in temperature characteristics and long term reliability by composing a quantum well layer of InAs and a barrier layer of InAlGaAs having band gap wavelength within a specified range. CONSTITUTION: The 2μm semiconductor laser comprises an n-type InAlAs clad layer 2 and an n-type InAlGaAs optical confinement layer 3 having composition of 200nm thick/1.4μm wavelength laminated on the upper surface of an n-type InP substrate 1. An In As strained quantum well layer 4 of 2nm thick and an InAlGaAs barrier layer 5 having composition of 10μm thick/1.4μm wavelength and band gap wavelength of 1.3-1.5μm are laminated alternately by two periods thus forming a multiple quantum well active layer. Subsequently, a p-type InAlGaAs optical confinement layer 6 having composition of 200nm thick/1.4μm wavelength, a p-type InAlAs clad layer 7, a p-type InGaAs cap layer 8 and a p-electrode 9 are laminated thereon. Finally, an n-electrode 10 is formed on the lower surface of the n-type InP substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a 2 μm band semiconductor laser, and more particularly to a highly reliable 2 μm band semiconductor laser having a low oscillation threshold and operating current, excellent temperature characteristics.

[0002]

2. Description of the Related Art A high power semiconductor laser of 2 .mu.m band (.about.1.9 .mu.m) has recently been attracting attention as an excitation light source of an eye-safe solid laser for 2.1 .mu.m band laser radar. 2μ
An example of an m-band high-power semiconductor laser is one using an InGaAs strained quantum well active layer on an InP substrate (see, for example, JS Major et al., IE Photonics Technology Letters (IEEE P
photonics Technology Lette
rs) No. 5, 594 to 596 (1993
Year)).

FIG. 3 shows a cross-sectional layer structure of a conventional 2 μm band semiconductor laser. This semiconductor laser has an n-type InP substrate 2
1, an n-type InP clad layer 22, an n-type InGaAsP optical confinement layer 23 having a wavelength of 1.3 μm, and a layer thickness of 7 n
m In _0.75 Ga _0.25 As strained quantum well layer (1.5% compressive strain) 24 and an InGaAsP barrier layer 25 having a wavelength of 1.3 μm alternately stacked for two periods, and a wavelength of 1.3 μm. Composition p-type InGaAsP optical confinement layer 26, p-type InP clad layer 27, p-type InG
It is composed of an aAs cap layer 28, ap electrode 29, and an n electrode 30. Resonator length 1000 μm, active layer width 200 μ
m, semiconductor laser front / rear surface reflectance of 10% /
With a 90% semiconductor laser, the oscillation wavelength is 1.9 μm,
The characteristics of the oscillation threshold of 500 mA at 10 ° C., the operating current of 2.3 A at the time of output of 500 mW, and the characteristic temperature of 55 K of the oscillation threshold at 10 to 30 ° C. are obtained.

Further, Japanese Patent Laid-Open No. 4-49689 discloses I
There is a description of a strained quantum well semiconductor laser using an nP substrate and an InGaAsP barrier layer, in which the well layer is made of InAsP.

[0005]

Since the conventional 2 μm band semiconductor laser has a small characteristic temperature of about 55 K, temperature control is required.

In a semiconductor laser using a strained quantum well, crystal dislocation occurs when the product of strain amount and layer thickness exceeds a critical value. In the strain quantum well layer 24 of the conventional 2 μm band semiconductor laser shown in FIG. 3, when the strain amount is 1.5% and the layer thickness is 7 mm (the product of the strain amount and the layer thickness = 10.5% · nm), it becomes almost the critical value. ing. Therefore, there has been a problem in long-term reliability of the semiconductor laser.

Further, the semiconductor laser described in Japanese Patent Laid-Open No. 4-49689 is a semiconductor laser in the 1.5 μm band and is not intended for the 2 μm band.

The object of the present invention is 2 μm, which has a low oscillation threshold and operating current, excellent temperature characteristics and long-term reliability.
It is to provide a band semiconductor laser.

[0009]

A 2 μm band semiconductor laser according to the present invention is a 2 μm band semiconductor laser in which a strained quantum well is used as an active layer on an InP substrate and an oscillation wavelength is 1.8 to 2.1 μm. The layer is InAs and the barrier layer is InAlGa having a bandgap wavelength of 1.3 to 1.5 μm.
It is characterized by using As.

Further, in a 2 μm band semiconductor laser in which a strained quantum well is used for an active layer and an oscillation wavelength is 1.8 to 2.1 μm on an InP substrate, a quantum well layer has InAs and a barrier layer has a bandgap wavelength of 1. In of 2 to 1.4 μm
It is characterized by using GaAsP.

[0011]

In the first 2 μm band semiconductor laser of the present invention, InAs is used for the strained quantum well layer. As a result, the amount of compressive strain is increased and the hole state density is reduced. Further, since the product of the strain amount and the layer thickness can be halved as compared with the conventional InGaAs strain quantum well layer, crystal dislocation does not occur in the strain quantum well layer. Therefore, a 2 μm band semiconductor laser having excellent long-term reliability can be obtained.

In addition, by using InAlGaAs for the barrier layer, the conduction band discontinuity between the quantum well layer and the barrier layer is increased to suppress the overflow of electrons from the quantum well layer to the barrier layer. Here, as the barrier layer bandgap wavelength is made smaller, the optical confinement layer in the quantum well layer becomes smaller, but the bandgap wavelength becomes 1.3.
The characteristic of the semiconductor laser becomes optimum in the range from 1.5 μm to 1.5 μm.

In the second 2 μm band semiconductor laser of the present invention, InAs is used for the strained quantum well layer.
As in the case of the 2 μm band semiconductor laser, the compressive strain amount can be increased, the hole state density can be reduced, and a highly reliable 2 μm band semiconductor laser can be obtained.

In addition, by using InGaAsP for the barrier layer, the valence band discontinuity between the quantum well layer and the barrier layer is increased to enhance the quantum confinement effect for holes and further reduce the hole state density. Here, as the barrier layer bandgap wavelength is made smaller, the optical confinement layer in the quantum well layer becomes smaller, but the characteristics of the semiconductor laser become optimum at the bandgap wavelength of 1.3 to 1.5 μm.

[0015]

FIG. 1 shows the first embodiment of the present invention, 2 .mu.m.
2 shows a sectional layer structure of a band semiconductor laser. In FIG. 1, the semiconductor laser comprises an n-type InAlAs cladding layer 2 on an n-type InP substrate 1, an n-type InAlGaAs optical confinement layer 3 having a layer thickness of 200 nm / wavelength of 1.4 μm, and an InAs strained quantum well layer having a layer thickness of 2 nm. (2.5% compressive strain) 4 and layer thickness 10
a multiple quantum well active layer in which two cycles of InAlGaAs barrier layers 5 having a composition of nm / wavelength of 1.4 μm are alternately laminated, and a p-type InAlGa having a composition of 200 nm / wavelength of 1.4 μm.
As optical confinement layer 6 and p-type InAlAs clad layer 7
, P-type InGaAs cap layer 8, p-electrode 9, and n
And electrode 10.

FIG. 2 shows the second embodiment of the present invention, 2 μm.
2 shows a cross-sectional layer structure of an m-band semiconductor laser. In FIG. 2, the semiconductor laser includes an n-type InP clad layer 12 on an n-type InP substrate 11, an n-type InGaAs optical confinement layer 13 having a layer thickness of 200 nm and a wavelength of 1.3 μm, and an I-layer having a layer thickness of 2 nm.
nAs strained quantum well layer (2.5% compressive strain) 14 and layer thickness 10
InGaAsP barrier layer 1 having a composition of nm / wavelength of 1.3 μm
A multi-quantum well active layer in which two periods of 5 are alternately laminated, and p-type InGaAs having a composition of layer thickness 200 nm / wavelength 1.3 μm
A P light confinement layer 16, a p-type InP clad layer 17,
p-type InGaAs cap layer 18, p-electrode 19, n
And electrodes 20.

FIGS. 4, 5 and 6 show a resonator length of 1000 μm.
m, active layer width 200 μm, front surface: rear surface reflectance 10%: 90% respectively, and characteristics of 2 μm band semiconductor laser and conventional semiconductor laser to which the first and second embodiments of the present invention are applied are calculated. And shows the temperature dependence of the oscillation threshold (I _th ) and the 500 mW output operating current (I _op ). From the respective figures, the dependency of the semiconductor characteristics on the barrier layer bandgap wavelength (assumed to be equal to the optical confinement layer bandgap wavelength) of each semiconductor laser can be seen.

In a conventional semiconductor laser having a barrier layer bandgap wavelength of 1.3 μm, as shown in FIG. 6, an oscillation threshold of 500 mA at 10 ° C., an operating current of 1.8 A at 500 mW output, and characteristics at 10 to 30 ° C. The temperature was 55 K, which is in good agreement with the previously reported values of semiconductor characteristics.

Further, it can be seen that there is an optimum value for the oscillation threshold in each of the figures.

FIG. 4 shows the calculation result when the first embodiment is applied. In the first embodiment, the oscillation threshold value 4 at 10 ° C. (with the bandgap wavelength of the barrier layer being 1.4 μm) is 4
Operating current at output of 00mA, 500mW 1.7A, 10
It can be seen that a characteristic temperature of 100K at -30 ° C is obtained.

Further, FIG. 5 shows the case where the second embodiment is applied (with the bandgap wavelength of the barrier layer being 1.3 μm), the oscillation threshold value at 10 ° C. is 400 mA, 5 as in the first embodiment.
It can be seen that a characteristic of an operating current of 1.7 A at an output of 00 mW and a characteristic temperature of 100 K at 10 to 30 ° C. can be obtained.

Since the characteristic temperature of the 2 μm band semiconductor laser of the present invention is as large as about 100 K, the conditions for temperature control of the semiconductor can be relaxed.

Further, in the first embodiment, as shown in FIG. 4, the semiconductor characteristics due to the change in the bandgap wavelength of the barrier layer are small, so that the control conditions for crystal growth are relaxed, and a semiconductor laser excellent in manufacturing yield can be provided.

In the first embodiment, the InAs strained quantum well layer /
Utilizing the fact that the group V element composition does not change at the quantum well / barrier interface because an InAlGaAs barrier layer is used, strain is applied to the barrier layer in the direction opposite to the strained quantum well layer, and the average strain amount is 0 in the multilayer structure. By so doing, the reliability of the semiconductor laser can be further improved.

InA was used as the cladding layer in the first embodiment.
Although 1As is used, InP may be used, and InP may be used for the cladding layer in the second embodiment, but the same effect can be obtained with InAlAs.

[0026]

As described above, according to the present invention, 2 μm
A semiconductor laser having a low oscillation threshold and operating current, excellent temperature characteristics, and high reliability can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross-sectional layer structure of a semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a sectional layer structure of a semiconductor laser according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a cross-sectional layer structure of a conventional semiconductor laser.

FIG. 4 is a diagram showing calculation results of temperature dependence of an oscillation threshold (I _th ) and a 500 mW output operating current (I _op ) of the semiconductor laser of the first embodiment.

FIG. 5 is a diagram showing calculation results of temperature dependence of an oscillation threshold value (I _th ) and a 500 mW output operating current (I _op ) of the semiconductor laser of the second embodiment.

FIG. 6 is a diagram showing calculation results of temperature dependence of an oscillation threshold (I _th ) and a 500 mW output operating current (I _op ) of a conventional semiconductor laser.

[Description of Reference Signs] 1,11,21 n-type InP substrate 2 n-type InAlAs clad layer 3 n-type InAlGaAs optical confinement layer with wavelength 1.4 μm composition 4,14 InAs strained quantum well layer 5 InAlGaAs barrier with wavelength 1.4 μm composition Layer 6 p-type InAlGaAs optical confinement layer having a wavelength of 1.4 μm 7 p-type InAlAs clad layer 8, 18, 28 p-type InGaAs cap layer 9, 19, 29 p-electrode 10, 20, 30 n-electrode 12, 22 n-type InP Cladding layer 13 n-type InGaAsP optical confinement layer having a wavelength of 1.3 μm 15 InGaAsP barrier layer having a wavelength of 1.3 μm 16 p-type InGaAsP optical confinement layer having a wavelength of 1.3 μm 17, 27 p-type InP clad layer 23 wavelength 1. 3 μm composition n-type InGaAsP optical confinement layer 24 In _0.75 Ga _{0.2 5} As strained quantum well layer 25 InGaAsP barrier layer having a wavelength of 1.3 μm 26 P-type InGaAsP optical confinement layer having a wavelength of 1.3 μm

Claims (2)

[Claims] 1. In a 2 μm band semiconductor laser in which a strained quantum well is used as an active layer and an oscillation wavelength is 1.8 to 2.1 μm on an InP substrate, a quantum well layer has InAs and a barrier layer has a bandgap wavelength of 1. InA of 3 to 1.5 μm
A 2 μm band semiconductor laser using 1 GaAs. 2. In a 2 μm band semiconductor laser in which a strained quantum well is used as an active layer and an oscillation wavelength is 1.8 to 2.1 μm on an InP substrate, a quantum well layer has InAs and a barrier layer has a bandgap wavelength of 1. InG of 2 to 1.4 μm
A 2 μm band semiconductor laser using aAsP.