JPH0344987A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser capable of high output performance with a minimum of temperature dependence using a material whose lattice constant in its active layer is smaller than that of a substrate and further reducing its thickness to minimize a band gap. CONSTITUTION:A semiconductor laser's active layer comprises GaInAsP quantum well barrier layers 6, 8, and 10, whose lattice constant is identical to an InP substrate 1, and GaInAs quantum well layers 7 and 9, which are provided with a lattice constant smaller than InP and whose one layer is thinner than a critical thickness in which a misfit dislocation is generated. Under this construction, the quantum well layers 7 and 9 are subject to tensile stress and produces lattice deformation due to mismatching of lattice so that the lattice constant of the substrate in a parallel direction may conform to that of InP and reduce the value in a vertical direction. As a result, the band gap is reduced compared with the absence of stress. It is, therefore, possible to improve the temperature dependence and carry out continuous oscillation at high temperature and high output performance at high temperature as well.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor laser used as a light source in an optical transmission system.3 [Prior Art] A semiconductor laser is not used as a light source in an optical transmission system. Gure 7
It has C characteristics and has been used more widely than before.
Ru. In particular, long-wavelength semiconductor lasers using Ga I nAsP/I nP DUB/L and heterostructure sound have wavelengths that are important as light sources for long-distance transmission because their oscillation wavelengths match the low-loss region of optical fibers. Lasers with wavelengths of 1.3 μm and 1.55 μm have been put into practical use.

[Problem to be solved by the invention]

However, the problem with this GaInAgP/InP Ly laser is that when the ambient temperature rises, its threshold current increases significantly, that is, the temperature dependence of the threshold current is large. Because of their own characteristics, continuous oscillation at temperatures above 100° C. is not easy, and high output operation at high temperatures is difficult.

The purpose of the present invention is to solve the problem of long-wavelength semiconductor lasers in which the threshold current has a large temperature dependence, reduce the temperature dependence, and enable continuous oscillation at high temperatures. The object of the present invention is to provide a semiconductor laser capable of output operation.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a semiconductor laser formed on an InP substrate, in which the active layer of the semiconductor laser includes a GaInAsP quantum well pariah layer having a lattice constant equal to that of InP, and a semiconductor laser formed on an InP substrate. has a small lattice constant,
The device is characterized in that it is composed of a QaInAs quantum well layer whose thickness is thinner than the critical thickness at which misfit dislocations occur.

[Effect]

In the present invention, a material in which the lattice constant of the semiconductor thin film of the active layer is smaller than that of the substrate and the cladding layer is used, and the thickness of one layer is made thinner than the critical thickness at which misfit dislocations occur. By reducing the bandgap of the active layer without introducing a light-emitting center, it is possible to obtain a semiconductor laser in which the threshold current does not increase even at high temperatures.

Incidentally, research has been actively conducted on semiconductor lasers that oscillate at a wavelength of 1.55 μm, which is the wavelength at which optical fiber loss is minimal. The most common one is G whose lattice constant matches that of InP and whose emission wavelength is 1.55 μm.
This is a laser that uses an aInAsP quaternary mixed crystal for the active layer, an InP'i substrate, and a cladding layer.

In this case, the characteristic temperature To (however, the characteristic temperature To representing the temperature dependence of the threshold current Ith
o)) It is difficult to achieve continuous oscillation at temperatures above 100° C., which corresponds to .50 to 60° C., and in particular, it has been impossible to obtain high optical output. For this reason, a laser with a small temperature dependence of threshold current, t! Aiming for a laser with large +To, Ga6.47In whose lattice constant matches InP
(Lasers using 1,51All or GaInAmP mixed crystals with a superlattice structure in the active layer have been studied. However, the value of To does not change at all, and high optical output at high temperatures has not been obtained. .

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a semiconductor laser illustrating an embodiment of the present invention. In the figure, 1 is an n-type InP substrate, 2 is a p-type InP substrate, and 2 is a p-type InP substrate.
3 is a p-type GaInAsP cap layer, 4 is an Fs-doped high-resistance InP buried layer, and 5 is an n111Ga layer with a wavelength of 1°15 μm that is lattice matched to TnP.
InAsP guide layers 6, 8 and 10 are GILInAIP quantum well pariah layers with a wavelength of 1.3 μm that are lattice matched to InP, and 7 and 9 are Ga6.
ByIno, 43Al quantum well layer, 11 is the n-type Ga
p-type GaInAsP with the same composition as InAsP guide layer 5
The n-type GaInAsP guide layer 5 to the p-type GaInAiP guide layer 11 constitute a quantum well active layer. Further, 12 is a p-type electrode, and 13 is an n-type electrode. Here, the n-type InP substrate 1 also serves as an n-type InP cladding layer.

Now, what determines the oscillation wavelength of a semiconductor laser with such a structure is the band gap of the cao, gγIno, 4sA-quantum well layers T and 9, but the quantum well layer 7.9 is Biaxial tensile stress (t・n5i
on), and the lattice constant in the parallel direction of the substrate matches that of InP, while the lattice constant in the vertical direction becomes smaller (second
figure). As a result, the band gap of quantum well layers 7 and 9 becomes smaller than the value without stress. However, FIG. 2 shows the state of lattice deformation of the quantum well layer constituting the laser of this example, in which 21 is the lattice of the GaInAaP pariah layer lattice-matched to InP, 22 is the lattice of the GILD,
57In (1,43As lattice is shown respectively, and 2
3 indicates biaxial tensile stress.

FIG. 3 shows the relationship between this stress and the amount of change in band gap. When the lattice constant is larger than that of InP, the band gap is large, and when it is small, the band gap is small. Cab, S? In0.4
The 3As quantum well layers 1 and 9 are made of G having the same lattice constant as InP.
When grown on the aInAsP layer, the bandgap changes from the original 0.86 sV to 0.80 eV. The laser with the structure shown in Figure 1, which has this quantum well layer, has 1
, oscillates at 55 μm. The temperature dependence of the oscillation threshold current Ith of this laser is shown in FIG. 4, where the characteristic temperature T.

The value has been improved to 100K, making continuous oscillation operation at high temperatures easier. Compared to the conventional 1.55 μm laser, the laser of the present invention suppresses non-radiative recombination phenomena such as the Auger effect due to the effect of tensile stress.
! This is because of this. Also, as a result, 5 rnW at 100℃
We were able to obtain high optical output.

〔Effect of the invention〕

As explained above, the present invention uses a material in which the lattice constant of the quantum well layer, which determines the bandgap of the active layer, is smaller than that of the substrate or cladding layer, and furthermore, the thickness of one layer is reduced to a critical point where misfit dislocations occur. By reducing the thickness and reducing the bandgap of the active layer without introducing non-emissive centers, there is an advantage that a semiconductor laser whose threshold current does not increase significantly even at high temperatures can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a semiconductor laser according to an embodiment of the present invention, FIG. 2 is a diagram showing the state of lattice deformation of the quantum well layer constituting the semiconductor laser of the above embodiment, and FIG. 3 is a diagram showing the same embodiment as above. FIG. 4 is a diagram showing the relationship between the lattice mismatch and the amount of change in band gap in FIG. 4, and FIG. 4 is a diagram showing the temperature dependence of the threshold current in the above embodiment. 1...n-type InP substrate, 2...p-type InP cladding layer, 3...p-type QaInAmP cap layer, 4
-...F. Doped high-resistance knee reinforcement layer, 5...
・N-type GaI with a wavelength of 1.15 μm that is lattice matched to InP
nAmP guide layer, 6, 8.1... All 1nAsP quantum wells with a wavelength of 1.3 μm that lattice-matches to InP 7, 9... Ga, which has a smaller lattice constant than InP.
Q, 57 In O, 43 As quantum well layer, 11...
... p-type GaInAsP guide layer, 12 ... p-type electrode, 13 ... n-type electrode.

Claims (1)

[Claims] In a semiconductor laser formed on an InP substrate, the active layer of the semiconductor laser is made of Ga having the same lattice constant as InP.
A semiconductor laser comprising an InAsP quantum well pariah layer and a GaInAs quantum well layer which has a lattice constant smaller than that of InP and whose thickness is thinner than the critical thickness at which misfit dislocations occur.