JPH04130689A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To reduce an oscillation threshold value and to perform a continuous oscillation by forming a well structure of an energy band due to a difference of composition ratios of an active layer doped with Al of a photoconductive layer and a light confining layer and applying a compression stress to the active layer. CONSTITUTION:An n-type AlGaInP clad layer 5, an AlGaInP photoconductive layer 6 and a p-type AlGaInP clad layer 7 are provided, and a well structure of an energy band is formed in the layer 6. Electrons and holes injected from an n-type electrode 3 and a p-type electrode 11 are confined in an AlGaInP strain active layer 62 to irradiate a light. Here, the lattice constant (a) of the layer 62 becomes larger by predetermined a than that (a) of an n-type GaAs substrate 2 and a compression stress is always applied, thereby reducing an oscillation threshold value. Accordingly, an oscillation threshold value is enhanced by Al doping to perform a continuous oscillation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser, and particularly to a semiconductor laser suitable for emitting visible light.

[Conventional technology]

Until a few years ago, most cases of obtaining bright red laser light utilized HeNe gas lasers.

Recently, visible light semiconductor lasers with Ga I nP as an active layer have been put into practical use, and it has become possible to obtain light with a wavelength of 0.67 μm using semiconductor lasers.

[Problem to be solved by the invention]

However, since the wavelength of 0.67 μm is longer than the wavelength of 0.6328 μm of the HeNe gas laser, its visibility is lower than that of the HeNe gas laser. Therefore, in the field of semiconductor lasers, there is a demand to further shorten the wavelength to approach the wavelength of HeNe gas laser, 0.6328 μm.

On the other hand, it has been found that adding Al to the active layer can shorten the emission wavelength. However, when Aft is added to the active layer, the number of non-radiative recombination centers related to AI increases, and the carrier confinement deteriorates due to the large bandgap of the active layer, resulting in a decrease in laser oscillation. This makes it difficult for continuous oscillation to occur at room temperature. Even if continuous oscillation is possible, its lifetime is short.

An object of the present invention is to solve these problems.

[Means to solve the problem]

In order to solve the above problems, the semiconductor laser of the present invention includes:
The optical waveguide layer is composed of an AlGaInP active layer and an AlGaInP optical confinement layer sandwiching it from above and below, and due to the difference in composition ratio between the active layer and the optical confinement layer, an energy band well structure is formed and the active layer Compressive stress is applied.

[Effect]

Since compressive stress is applied to the active layer, the oscillation threshold is lower than when no compressive stress is applied. Therefore, it is possible to resist an increase in the oscillation threshold due to the addition of AN, and continuous oscillation at room temperature is possible.

In addition, this compressive stress is given by strain based on the difference in lattice constant of the active layer with respect to the GaAs substrate, so it needs to be thin enough to prevent dislocations. Since the optical waveguide layer is provided, a sufficient thickness can be ensured for the entire optical waveguide layer. therefore,
Problems caused by the thickness of the optical waveguide layer, such as the vertical spread of emitted light, can be suppressed in the same manner as in the past.

Note that it is difficult to obtain a laser that continuously oscillates at room temperature with a wavelength of 0.64 μm or less using conventional techniques, and the present invention is particularly useful in such cases.

[Embodiment] FIG. 1 is a cross-sectional structural diagram showing an embodiment of the present invention. This semiconductor laser 1 uses an n-GaAs substrate 2 as a substrate. An n-type electrode 3 is formed on the back surface of the n-GaAs substrate 2, and an n-A470aInP cladding layer 5, A#Ga1 is formed on the top surface via an n-GaAs buffer layer 4.
An nP optical waveguide layer 6, a p-AllGa1nP cladding layer 7, and a p-GaInP layer 9 are sequentially laminated by epitaxial growth. The AJGalnP optical waveguide layer 6 has a three-layer structure, with the AJGalnP optical confinement layer 61, A
It is composed of an IGaJnP strained active layer 62 and an AjGalnP optical confinement layer 63. The refractive index of the optical waveguide layer 6 is that of the n-AlGaInP cladding layer 5 and the p-Al
Since it is higher than the GaInP cladding layer 7, s A I G
The laser light generated in the a I n P strained active layer 62 is confined within the optical waveguide layer 6 . p-AlGaInP
As shown in the figure, both shoulder portions of the cladding layer 7 are etched away to form a mesa portion extending in a direction perpendicular to the plane of the paper.

An n-GaAs block layer 8 is buried in the etched portion to almost the same height as the surface of the p-GalnP layer, and a p-GaAs contact layer 10 and a p-electrode 11 are further formed on this surface. ing. Note that the carrier concentration of each layer is n=2×10 c+o for the n-GaAs substrate 2 and the n-GaAs buffer layer 4.
n-2Xn-2 in n-AIGaInP cladding layer 5
p-5X in X1017-ANGalnP cladding layer 7
1017an p-G a I n P layer 9 and p-GaAs contact layer 10 with p = 2 x 1
There are 018cm-3te. Also, the thickness of each layer is n-Ga
The As substrate 2 has a thickness of 80 μm, and the GaAs buffer layer 4 has a thickness of 0.5 μm.

1 with n-AlGaInP cladding layer 5. czm, 0.21 pm for the optical waveguide layer 6, 1 μm for the Ga I nP cladding layer 7 (however, 0.5 μm for both shoulders)
% n-GaAs block layer 8 with a thickness of 0.2 μm.

O=3 am in the p-GaAs contact layer 10.

Figure 2 shows n-Aj) GalnP cladding layer 5, AllG
It is an energy band diagram in the a1nP optical waveguide layer 6 and the p-/1j7GalnP cladding layer 7.

In this way, an energy band well structure is created within the optical waveguide layer 6. Therefore, n electrode 3 and p[pole 1
The electrons and holes injected from 1 are in this well, that is, A
It is confined within the lGaInP strained active layer 62, where light emission occurs.

What is unique about this example is the AI? The lattice constant of the Ga1nP strained active layer 62 is larger than the lattice constant a of the n-GaAs substrate 2 by Δa. Specifically, Δa
/a- There is a deviation of about 0.3% to 1%. On the other hand, including AlGaInP optical confinement layers 61 and 63,
Aj) The lattice constants of the epitaxial layers other than the GalnP strained active layer 62 substantially match that of the n-GaAs substrate 2. Therefore, compressive stress is always applied to the A,pGalnP strained active layer 62.

Therefore, the oscillation threshold can be lowered than when no compressive stress is applied.

This is extremely effective for visible light semiconductor lasers in which the oscillation threshold increases due to Al addition and continuous oscillation is difficult, that is, visible light semiconductor lasers having ANGalnP as an active layer.

By the way, when strain is applied due to differences in lattice constants, dislocations will occur unless the thickness of the layer undergoing strain is made sufficiently thin. Regarding Ga1nP, the relationship between the amount of strain and the maximum film thickness (critical film thickness) at which dislocations do not occur can be found at the 5th OMVPE International Conference (19
1990) has already been reported, and it is thought that it is almost the same for A and 90alnP.

In this example, CARGa ) Inx l
-x y 1-y P, the composition ratio of the Al)GalnP strained active layer 62 is x-0,26, y-0,43, and the composition ratio of the AlGaInP optical confinement layers 61 and 63 is x-0,45 ,y
s++Q, 5, and the composition ratios of the n-AlGa I nP cladding layer 5 and the p-ANGalnP cladding layer 7 are x-0.7, y-0.5. The deviation of the lattice constant of this AjJGalnP mixed crystal semiconductor with respect to the GaAs semiconductor is
Determined by the value of y, the AlGaInP strained active layer 6
Only No. 2 has a lattice constant shifted from that of the n-GaAs substrate 2. In the configuration of this example, AlGaInP
If the thickness of the strained active layer 62 is 0.01 μm (100 A), no dislocation will occur. Note that if the well is thin, it becomes a quantum well, but in the present invention, the quantum effect is not so important, and it is important that strain is applied. Also, in general,
If the active layer is too thin, the emitted light will spread in the vertical direction due to diffraction, but in this structure, the optical confinement layers 61 and 62 are provided to ensure a sufficient thickness for the optical waveguide layer 6. Therefore, the spread of the emitted light can be suppressed.

By the way, when the semiconductor laser of this example was experimentally driven, it was confirmed that it not only achieved continuous oscillation, but also exhibited extremely unique characteristics. That is, when the semiconductor laser of this example was driven at a temperature of -6 DEG C., its current-light output characteristics had an inverted S-shape as shown in FIG. 3(a). There has been no such report so far, and this seems to indicate that a light emitting process different from that in a normal active layer occurs within the strained active layer 62. The stripe width of the semiconductor laser used in this experiment was 5
μm, and the wavelength of the emitted laser light is approximately 0.62 μm.
It is m. This phenomenon is not only new, but also industrially useful. For example, if used in combination with a normal laser with characteristics as shown in Figure 3(b), the total current-light output characteristics will be as shown in Figure 3(c), and the area A shown in the figure will be In this case, stable optical output can be obtained against current changes.

FIG. 4 shows an energy band diagram of another embodiment of the present invention. In this embodiment, in order to obtain high output from the laser, the AIGaInP strained active layer 62 of the optical waveguide layer 6 has a multilayer well structure.

The composition of the well layer 65 and barrier layer 66 is (AIxGa
) In P, the well layer 65 is 1-x
y 1-y x-0,2, y-0,43, and the barrier layer 66 is x-
0,2, ymQ, 36. Note that the AlGaInP optical confinement layer 61, the AjJGalnP optical confinement layer 63,
n-AllGa1nP cladding layer 5 and p-Al1
The composition of the Ga I nP cladding layer 7 is the same as in the first embodiment described above. Moreover, the layer thickness of the optical waveguide layer 6 is 0.
The layer thicknesses of the 3 μm one-well layer 65 and the barrier layer 66 are 100 A and 50 A, respectively.

Generally, in a multilayer well structure, as the total thickness of the wells increases, dislocations tend to enter even if the thickness of each well is less than the critical film thickness. On the other hand, in this embodiment, the lattice constant is selected so that stress in the opposite direction to that of the well layer 65, that is, tensile stress, is applied to the barrier layer 66. As a result, the stress in the entire InP strained active layer 62 is suppressed, and dislocations do not occur.

〔Effect of the invention〕

As explained above, according to the semiconductor laser of the present invention,
Since compressive stress is applied to the AlGaInP active layer,
The oscillation threshold becomes lower than when no addition is made. Therefore, continuous oscillation becomes possible, and visible light with a wavelength of 0.67 μm or less, which was difficult to obtain in the past, can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional structural diagram showing one embodiment of the present invention, Fig. 2 is an energy band diagram thereof, Fig. 3 is a diagram showing current-light output characteristics, and Fig. 4 is an energy band diagram of another embodiment. It is. 2-n-GaAs substrate, 5-n-AlGa
InP cladding layer, 6... optical waveguide layer, 7... p-
A11GaInP cladding layer, 61.63-ApGal
nP optical confinement layer, 62...Al)GalnP strained active layer.

Claims (1)

[Claims] 1. In a semiconductor laser using a GaAs substrate, an optical waveguide layer is composed of an AlGaInP active layer and an AlGaInP optical confinement layer sandwiching this from above and below, and the composition ratio of the active layer and the optical confinement layer is 1. A semiconductor laser characterized in that a well structure of energy bands is formed and compressive stress is applied to the active layer due to the difference in energy band. 2. The semiconductor laser according to claim 1, wherein the well structure is a multi-well structure, and a barrier layer separating each well is subjected to tensile stress.