JPH0513884A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To sufficiently increase an effective band difference between a quantum well layer and a light confinement layer by forming the light confinement layer of a compound semiconductor material containing phosphorus and having larger band gap than that of GaAs such as (AlyGa1-y)zIn1-zP (0<=y<1). CONSTITUTION:An optical waveguide layer is formed of an active layer having GaInAs quantum well layers 6a, 6b, 6c, 6d, and light confinement layers 4, 7 vertically holding the active layers from above and below. Here, as the material of the layers 4, 7, compound semiconductor containing phosphorus and having larger band gap than that of GaAs such as (AlyGa1-y)zIn1-zP (0<=y<1), is used, and a band gap difference between the layers 6a, 6b, 6c, 6d and the layers 4, 7, is increased as compared with that of prior art. Thus, a threshold value current is reduced, operating characteristics at a high temperature are improved, and an increase in an efficiency of a semiconductor laser and an increase in an output can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a 0.9 to 1.1 μm band semiconductor laser.

[0002]

2. Description of the Related Art A semiconductor laser of 0.9 to 1.1 μm band is
It is expected as a laser that supplements the wavelength range between the GaAs short wavelength laser and the InP long wavelength laser. In particular,
A semiconductor laser with an oscillation wavelength of 0.98 μm is expected to be a key technology for future optical communication. Er ³⁺
Practical use is awaited as a pumping light source for a doped fiber optical amplifier. As such a 0.9 to 1.1 μm band semiconductor laser, GaAs is used as the light confinement layer and GaI is used as the quantum well layer.
A device having a strained quantum well active layer composed of a GaAs / GaInAs heterojunction using nAs has been conventionally considered.

[0003]

In the case of this material system, the effective band gap difference between the quantum well layer and the light confining layer is, for example, 150 meV for a 0.98 μm laser.
It is only small and not large enough to cause recombination of holes and electrons in the active layer.

[0004]

The semiconductor laser of the present invention has been made in view of these problems.
The optical confining layer is composed of an active layer having a GaInAs quantum well layer and a light confining layer sandwiching the active layer from above and below. The optical confining layer contains phosphorus and has a bandgap larger than that of GaAs. compound semiconductor material, in which is formed, for example, _{(Al y Ga 1-y)} Z in 1-Z P (0 ≦ y <1).

[0005]

[Action] When used in the quantum well layer Ga _1-X In X As, the light confinement layer _{(Al y Ga 1-y)} Z In 1-Z P (0 ≦ y <1) to the material, the light closed The effective bandgap difference between the confinement layer and the quantum well layer is Ga, which is the material when y = 0 and z = 0.51 at least in the case of a 0.98 μm laser.
_0.51 In _0.49 P (1.85 eV) and Ga _1-x In _x As
The difference of (1.265 eV) is 585 meV, which is the conventional G
Band gap difference of aAs / GaInAs material system (~ 1
It is much larger than that of 50 meV).

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 relates to an embodiment of the present invention.
It is a figure for demonstrating the semiconductor laser of what is called a single quantum well structure.

FIG. 1A shows the cross-sectional structure of the emission surface of the laser, and FIG. 1B shows the energy band difference. As shown in FIG. 1A, a Si-doped GaAs buffer layer 2 and a Se-doped (Al
_0.5 Ga _0.5 ) In _0.5 P n-type cladding layer 3, non-doped Ga _0.5 In _0.5 P optical confinement layer 4, non-doped Ga
_0.75 In _0.25 As quantum well layer 6, undoped Ga _0.5 I
n _0.5 P optical confinement layer 7, Zn-doped (Al _0.5 G
The a _0.5 ) _0.5 In _0.5 P P type cladding layer 8 and the Zn-doped GaAs contact layer 9 are sequentially formed by epitaxial growth. Furthermore, the electrode 1 is formed under the GaAs substrate 1 and on the Zn-doped GaAs contact layer 9, respectively.
It has a structure in which 0 and 11 are formed. Rather than GaAs as a material of the light confinement layer 4 and 7 in this _{embodiment, (Al y Ga 1-y} ) Z In 1-Z P (0 ≦ y <1) at y = 0, z = 0.5 In this case, the material Ga _0.5 In _0.5 P is used. In this case, as described above, GaAs / G
The band gap difference is about 150 meV at the maximum when the aInAs material system is used, while the Ga _0.5 In
_{When 0.5} P is used, the band gap difference between the quantum well layer and the optical confinement layer can be made very large to about 585 meV, and effective recombination of carriers can be performed.

[0008] At this time, GaInAs and GaAs
Has a lattice mismatch of about 1.5%, but the thickness of the GaInAs quantum well layer is 60 angstroms, which is sufficiently thin so as to be strained within the elastic limit. Therefore, GaAs / GaInAs
Good crystallinity is maintained at the interface without crystal defects due to dislocations or the like.

FIG. 2 is a diagram for explaining a semiconductor laser having a so-called multiple quantum well structure according to this embodiment.
FIG. 1A shows the cross-sectional structure of the laser emission surface, FIG. 2B shows the band gap difference of the optical waveguide layer, and FIG. 1C shows the lattice constants of the quantum well layer and the barrier layer. Is. This semiconductor laser is, for example, Si-doped GaAs.
On the substrate 1, Si-doped GaAs buffer layer 2, Se-doped (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P n-type clad layer 3, non-doped (Al _0.2 Ga _0.8 ) _0.5 In _0.5 P
Light confinement layer 4, non-doped Ga _0.75 In _0.25 As quantum well layer 6 a, non-doped Ga _0.61 In _0.39 P barrier layer 5 a,
Non-doped Ga _0.75 In _0.25 As quantum well layer 6b, non-doped Ga _0.61 In _0.39 P barrier layer 5b, non-doped Ga
_0.75 In _0.25 As quantum well layer 6c, undoped Ga _0.61
In _0.39 P barrier layer 5c, undoped Ga _0.75 In _0.25 A
s quantum well layer 6d, non-doped (Al _0.2 Ga _0.8 ).
_0.5 In _0.5 P light confinement layer 7, Zn-doped (Al
_0.7 Ga _0.3 ) _0.5 In _0.5 P P-type cladding layer 8 and Zn-doped GaAs contact layer 9 are sequentially formed by epitaxial growth, and further Si-doped GaA is formed.
s substrate 1 below and Zn-doped GaA _S contact layer 9 on each of the electrodes 10 and 11 are formed.

[0010] Thus the light confinement layer 4 and 7 (Al _y G
a _1-y ) _Z In _1-Z P (0 ≦ y <1), y = 0.2, z
= 0.5, the material is (Al _0.2 Ga _0.8 ) _0.5.
In _0.5 P is used, and the quantum well layer is made of GaInAs. AlGaInP / GaInA of this embodiment
Also in the case of the material system of s, GaIn of the embodiment shown in FIG.
The energy gap difference is almost the same as that of P / GaInAs, and the energy gap difference between the optical confinement layer and the quantum well layer is very large as compared with the case of using the conventional GaAs / GaInAs material system.

The combination of the optical confinement layer and the quantum well layer is
(Al _y Ga _1-y ) _z In _1-z P / Ga _{1-x of this example}
Not only In _x As, but also Al _y Ga _1-y P _z As _1-z /
_{Ga 1-x In x As,} Al y In 1-y P z As 1-z / G
a _1-x In _x As, Gay _y In _1-y P _z As _1-z / Ga
_It can be also realized by using another compound semiconductor material containing phosphorus for the light confining layer, such as _1-x In _x As.

In addition, the active layer of this embodiment, as shown in FIG. 2 (c), is a GaInP forming barrier layers 5a-5c.
Has a lattice constant smaller than that of GaAs, which is a substrate material, and forms GaInAs forming the quantum well layers 6a to 6d.
Is larger than that of GaAs. Due to this lattice constant relationship, compressive stress is applied to the GaInAs quantum well layer and tensile stress is applied to the GaInP barrier layer. Since the semiconductor laser according to the present embodiment is configured in this way, the compressive stress of the quantum well layer and the tensile stress of the barrier layer cancel each other out in the entire active layer, and the average lattice constant of the active layer is GaAs.
However, the lattice constant of is less than 10 ^-3 .
Therefore, it is possible to increase the effective active layer thickness and increase the gain as compared with the case of the active layer having the single quantum well structure.

[0013]

Effect of the Invention] above, as described in detail, the material of the multiple quantum well structure and the semiconductor laser in the optical confinement layer of a single quantum well structure, for example, _{(Al y Ga 1-y)} Z In 1-Z P
(0 ≦ y <1) and phosphorus is included, and the band gap is Ga
By using GaInAs as the material of the compound semiconductor and quantum well layer larger than As, the band gap difference between the quantum well layer and the light confining layer can be made much larger than before. Therefore, since the threshold current can be reduced and the operating characteristics at high temperature can be improved, higher efficiency and higher output of the semiconductor laser can be realized. Also, in the semiconductor laser with multiple quantum well layers, since the material of the barrier layer has a small lattice constant, the compressive stress of the quantum well layer can be canceled by the tensile stress of the barrier layer, and the thickness of the entire active layer Can be freely designed without being restricted by the critical film thickness that causes dislocations.

[Brief description of drawings]

FIG. 1 is a view for explaining a semiconductor laser having a multiple quantum well structure of this embodiment.

FIG. 2 is a diagram for explaining a semiconductor laser having a single quantum well structure according to the present embodiment.

[Explanation of symbols]

1 ... GaAs substrate 4, 7 ... Light confinement layer 5a, 5b, 5c ... Barrier layer 6, 6a, 6b, 6c, 6d ... Quantum well layer

Claims (3)

[Claims] 1. A semiconductor laser formed on a GaAs substrate, wherein the optical waveguide layer comprises an active layer having a GaInAs quantum well layer.
A semiconductor laser comprising a light confining layer sandwiching the active layer from above and below, wherein the light confining layer is made of a compound semiconductor material containing phosphorus and having a bandgap larger than GaAs. 2. The compound semiconductor material of the light confinement layer is (Al
The semiconductor laser according to claim 1, wherein _y Ga _1-y ) _Z In _1-Z P (0 ≦ y <1). 3. The active layer comprises a plurality of GaInAs quantum well layers and barrier layers separating the well layers, and the material forming the barrier layers has a lattice constant smaller than that of GaAs. 1. The semiconductor laser described in 1.