JPH0245995A - Semiconductor laser device of quantum well structure - Google Patents

Abstract

PURPOSE:To make a narrow distribution of a light emitting wavelength by constituting a well layer in a grated layer whose composition rate varies gradually. CONSTITUTION:A well layer 2 which is formed between nondoped AlGaAs barrier layers 1, 3 is made in a grated layer whose composition rate of Al varies gradually. Then a quantum well whose potential shape changes smoothly is formed. Since fluctuation of a composition distribution of each atomic layer due to imperfect control of a film thickness is statistically independent, effect of fluctuation of different atomic layers compensate for each other, thus reducing a distribution width of laser light emitting wavelength and improving light emitting characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser device used as a light source for optical communication and consumer equipment, and particularly to a quantum well structure type semiconductor laser device.

[Prior art]

FIG. 2A is a structural diagram showing an example of an active layer of a semiconductor laser device using a conventional quantum well structure, and a graph showing the structure.

The barrier layer 13 is a non-doped AlGaAs barrier layer.

By making the thickness of the non-doped GaAs well layer 12 comparable to or smaller than the de Broglie wavelength of electrons, a quantum level is formed in the active layer, and the emission wavelength of the laser is determined in accordance with the level.

This level largely depends on the thickness of the non-doped GaAs well layer 12.

[Problem to be solved by the invention]

In a typical quantum well structure in which the thickness of the non-doped GaAs well layer 12 is on the order of several tens of nanometers, the emission wavelength changes by several tens of nanometers even if this value becomes only -1 atomic layer thick. On the other hand, ordinary M B E (Molecular B
eam E pitaxy) method and M OCV D (
MetalorganjcChemical Vapo
In a thin film growth technique such as a deposition method, irregularities of one to several atoms are generated on the growth surface, and therefore the well layer thickness of a quantum well fabricated by this growth technique also has fluctuations of the same degree. As a result, the emission wavelength of the laser is also distributed with some fluctuation, and due to the non-flatness of the growth surface,
The emission characteristics of the laser will deteriorate.

Advances in crystal growth methods have improved controllability of film thickness, and the characteristics of lasers using this quantum well structure have been greatly improved. However, fluctuations in the well layer thickness of about one atomic layer still exist, making it difficult to emit light. It has a negative effect on the characteristics.

The present invention has been made to solve the above problems.

An object of the present invention is to provide a technique that can reduce the influence of the imperfection in film thickness control on the energy level of a quantum well and improve the light emission characteristics of a semiconductor laser.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means to solve the problem]

A brief overview of typical inventions disclosed in this application is as follows.

The present invention provides a single quantum well in which a semiconductor thin layer having a first energy gap Eg is sandwiched between semiconductor thin layers having a second energy gap Egz (where Egz < Egz) or a multiple quantum well in which a plurality of these are stacked. In a quantum well structure type semiconductor laser device including a well in the active region, a mixed crystal layer of a material having a first energy gap Egz and a material having a second energy gap Egz is used as a barrier layer. The most important feature is that the composition ratio of the constituent elements is slowly changed atomic layer by atomic layer or every few atomic layers to create a quantum well in which the potential shape felt by conduction electrons or valence band holes changes smoothly. shall be.

That is, the most important feature of the quantum well used in a semiconductor laser is that the shape of the potential felt by conduction electrons or holes in the valence band changes smoothly.

[Effect]

To obtain the potential shape described above, a graded layer whose composition ratio changes continuously is used. In the case of a conventional quantum well using a heterointerface, the energy level is determined only by the thickness of the quantum well, whereas in the structure of the present invention, the energy level is determined by the composition ratio distribution of the entire graded layer. to differ greatly. Fluctuations in the composition ratio distribution due to imperfection in film thickness control also occur in the structure of the present invention, but due to the above-mentioned characteristics, only the effect of averaging the fluctuations of each atomic layer is exerted on the quantum level. In general, these fluctuations are statistically independent in each atomic layer, so the effects of fluctuations in different atomic layers cancel each other out, making it much more difficult than when fluctuations occur only in one atomic layer at the interface, as in conventional quantum wells. , the distribution width of the laser emission wavelength due to imperfection in film thickness control becomes much smaller.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be specifically described using the drawings.

In addition, in all the figures for explaining the embodiment, parts having the same functions are given the same reference numerals, and repeated explanations thereof will be omitted.

FIG. 1A is a graph showing a structural band structure of an example of an active layer of a semiconductor laser device using a quantum well structure of the present invention.

It is a non-doped AlGaAs barrier layer, and the A1 composition ratio is 0.
．． 5 AlGaAs layer. 2 is a non-doped graded well layer in which the A1 composition ratio is changed from 0.5 to O.
The quantum well layer has a structure in which the value decreases smoothly to 0.5 and then increases again to the value of 0.5, and its half-width a is 17.

3 is a non-doped AlGaAs barrier layer, which is an AlGaAs layer with an A1 composition ratio of 0.5.

As described above, the energy level of this non-doped graded well layer 2 is determined by the entire composition ratio distribution over ten or more atomic layers. Therefore, the influence of fluctuations in the composition ratio distribution caused by imperfect control of the film thickness is canceled out among the ten or so atomic layers.

As a result, in a semiconductor laser device using this quantum well structure, the distribution width of the emission wavelength can be reduced to 1/2 or less compared to a conventional device having the same emission wavelength.

In addition, in the above embodiment, the entire quantum well is smoothed by A1.
Although a graded layer is used in which the composition ratio changes, in a conventional quantum well structure, only a few atomic layers near the hetero interface that determines the energy level can be made into a graded layer.

Furthermore, although the above embodiment deals with the AlAs/GaAs system with a small lattice mismatch, it is also possible to use other compound semiconductor systems with a relatively large lattice mismatch because the graded layer alleviates the stress caused by the lattice mismatch. , excellent luminescent properties can be obtained.

In addition, in the above embodiment, a Gaussian function type composition ratio change was given to the quantum well layer, but a triangular or two-dimensional composition ratio change was given to the quantum well layer.
Any composition ratio change may be given as long as the quantum level is determined by the entire composition ratio distribution over a plurality of atomic layers, such as the following function.

The present invention has been specifically explained above based on examples, but
It goes without saying that the present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit thereof.

〔Effect of the invention〕

As described above, according to the present invention, in a semiconductor laser device, the influence that imperfection in film thickness control has on the laser emission wavelength is reduced by canceling each other between the atomic layers constituting the quantum well, and the emission of light is reduced. Since the wavelength distribution width is significantly reduced, the light emission characteristics of the semiconductor laser can be improved.

[Brief explanation of the drawing]

FIG. 1A is a structural diagram showing an example of the active layer of a semiconductor laser device using the quantum well structure of the present invention; FIG. 1) r; A1 composition ratio distribution diagram of the active layer in FIG. 1A; FIG. 1C is a graph showing the energy band structure of the active layer in FIG. 1A, FIG. 2A is a structural diagram showing an example of the active layer of a semiconductor laser device using a conventional quantum well structure, and FIG. 1A and FIG. 2C are , is a graph showing the energy band structure of the active layer of FIG. 2A. In the figure, 1... non-doped AlGaAs barrier layer, 2...
・Non-doped graded well layer, 3...Non-doped A
lGaAs barrier layer. A1 group 59↑

Claims (1)

[Claims] (1) A single quantum well in which a semiconductor thin layer with a first energy gap Eg_1 is sandwiched between semiconductor thin layers with a second energy gap Eg_2 (however, Eg_1<Eg_2) or a multiple quantum well in which multiple quantum wells are stacked. In a quantum well structure type semiconductor laser device included in an active region, a mixed crystal layer of a material having a first energy gap Eg_1 and a material having a second energy gap Eg_2 is used as a barrier layer, and this mixed crystal layer is composed of A quantum well structure semiconductor characterized by configuring a quantum well in which the potential shape felt by conduction electrons or holes in the valence band changes smoothly by slowly changing the composition ratio of elements every atomic layer or every few atomic layers. Laser equipment.