JPH0576794B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in semiconductor lasers, particularly single quantum well structure semiconductor lasers.

As a conventional example, an energy band diagram of the main parts of an AlGaAs/GaAs single quantum well structure semiconductor laser is shown in FIG. 1a, and a schematic diagram of the atomic arrangement is shown in FIG. 1b. In the figure, 1 is an n-type carrier confinement layer made of n-Alx ₁ Ga _1-x1 As (x ₁ ≠ 0), 2 is an active layer made of GaAs, and 3 is P-Alx ₂ Ga _1-x2 As (x ₂ ≠0). In FIG. 1b, hatched circles represent Al atoms, and white circles without hatching represent Ga atoms. Furthermore, the As atom is located at a position perpendicular to the plane of the paper and is not shown here. In the figure, the Al concentration of AlGaAs is approximately
This is the case of 0.3. As shown in this figure, the Al atoms are arranged in clusters. Therefore, the thickness of GaAs in the active layer 2 in the center of figure b should originally be 9 atomic layers, but it is 10 atomic layers.
It can be seen that in some places there are 11 atomic layers.
Therefore, when forming a quantum well structure using a carrier confinement layer of such a mixed crystal of Al and Ga, the thickness of the quantum well layer inevitably has a non-uniform thickness of 1 to 2 atomic layers. It ends up existing within the membrane plane. Such non-uniformity is accompanied by non-uniformity in quantization levels, which causes a broadening of the gain spectrum of the semiconductor laser and an increase in threshold current.

An object of the present invention is to provide a semiconductor laser that eliminates in-plane non-uniformity in a quantum well layer, has a narrow gain spectrum, and has a low threshold.

The semiconductor laser of the present invention includes an active layer, first and second semiconductor layers sandwiching the active layer above and below and made of a compound semiconductor made of two elements and having a larger forbidden band width than the active layer; Third and fourth semiconductor layers sandwiching a three-layer structure consisting of the first and second semiconductor layers and the active layer above and below, having a larger forbidden band width than the active layer, and made of a compound semiconductor made of at least three or more elements. a semiconductor layer;
The thicknesses of the second semiconductor layer and the second semiconductor layer are such that electrons and holes can pass therethrough by quantum mechanical tunneling.

Next, the present invention will be explained in detail with reference to the drawings.

A cross-sectional view of one embodiment of the present invention is shown in FIG. In the figure, 6 is an n-GaAs substrate, 7 is a buffer layer (n
-GaAs), 8 is an n-type cladding layer (n-
Alx ₈ Ga _1-x8 As, 0.2≦ _x8 ≦0.8, thickness 0.5-3μm)
1 is an n-type carrier confinement layer (n-Alx ₁ Ga _1-x1
As, 0.1≦ _x1 ≦0.4, _x1 < _x8 , thickness 0.05-0.3μm),
4 is n-type AlAs layer (thickness ≦20 Å), 2 is active layer (nondope GaAs, thickness ≦200 Å), 5 is P-type AlAs
layer (thickness ≦20 Å), 3 is a P-type carrier confinement layer (P-Alx ₃ Ga _1-x3 As, 0.1≦x ₃ ≦0.4, thickness 0.05~
0.3 μm), 9 is a P-type cladding layer (P-Alx ₉ Ga _1-x9
As, x ₉ > x ₈ , 0.2≦x ₉ ≦0.8, thickness 0.5 to 3 μm), 1
0 is the cap layer (P ⁺ -GaAs), 11 is the SiO ₂ film,
12 is a P-type electrode, 13 is an N-type electrode, and 14 is an electrode window. In this example, the n-type carrier confinement layer 1 is the third semiconductor layer, the n-type AlAs layer 4 is the first semiconductor layer, the P-type AlAs layer 5 is the second semiconductor layer, and the P-type carrier confinement layer 3 is the third semiconductor layer. This corresponds to 4 semiconductor layers. In this embodiment, since the n-type carrier confinement layer 1 and the P-type carrier confinement layer 3 work as light guide layers, so-called SCH (Separate Confinement) that confines light and carriers in separate layers is used.
Heterostuvucture) structure. Figure 3a shows the energy band diagram near the active layer of this example.
A schematic diagram of the atomic arrangement is shown in FIG. 3b. The difference from the conventional example is that the n-type AlAs layer 4 and the p-type AlAs layer 5
The point is that it has the following. In FIG. 3b, as in FIG. 1b, diagonal circles indicate Al atoms, and open circles indicate Ga atoms. As shown in Figure 3b, the n-type AlAs layer 4
It can be seen that since the active layer 2 is sandwiched between the P-type AlAs layer 5 and the active layer 2 above and below, the thickness of the active layer 2 is 9 atomic layers uniformly within the film surface. Therefore, since the thickness of the active layer 2 is uniform, the quantization level is uniform within the film plane, the gain spectrum is narrow, and low threshold current oscillation is possible. In addition, since the thickness of the n-type AlAs layer 4 and the p-type AlAs layer 5 is as thin as two atomic layers in FIG. Can be injected.

Next, the manufacturing method of this example will be explained. First, a buffer layer 7 is placed on an n-GaAs substrate 6,
n-type cladding layer 8, n-type carrier confinement layer 1,
An n-type AlAs layer 4, an active layer 2, a p-type AlAs layer 5, a p-type carrier confinement layer 3, a p-type cladding layer 9, and a cap layer 10 are successively crystal-grown. The crystal growth method is
Any method such as MBE method, MO-CVD method, VPE method, etc. may be used. Next, a SiO ₂ film 11 is formed,
Electrode windows 14 are formed by photoetching. Next, a P-type electrode 12 and an N-type electrode 13 are formed to establish ohmic contact. Finally, the wafer is cut into pellets using cleavage or the like, then fused to a stem or the like, and electrode wires are attached to complete the pellets.

In this example, the SCH structure was used, but
Not limited to this, for example, GRIN-SCH (Graded-
Index Waveguide Separate−Confinement−
It is clear that the present invention can also be applied to other structures such as Hetevostructure. In addition, in this example, the SiO ₂ film stripe structure was used as the electrode confinement structure, but the current confinement structure is not limited to this, and any current confinement structure such as a planar stripe structure, a ridge wave guide structure, or a buried structure can be used. The present invention can be applied. Further, in this embodiment, GaAs was used for the active layer, but the effect is expected to be obtained even if AlGaAs is used. Further, although an n-GaAs substrate is used in this embodiment, it is obvious that the present invention is not limited to this, and a P-GaAs substrate may be used, with all the conductivity types of this embodiment being reversed. Further, in this embodiment, an n-type AlAs layer is provided on the n-side and a p-type AlAs layer is provided on the p-side, but the present invention is not limited to this, and the effects of the present invention can be expected even if the AlAs is non-doped or of the opposite conductivity type.
Furthermore, although AlGaAs/GaAs-based materials are used in this embodiment, it is clear that the present invention can be applied to other materials such as AlGaSb/GaSb-based materials.

[Brief explanation of the drawing]

FIG. 1a is an energy band diagram of the main part of a conventional AlGaAs/GaAs single quantum well structure semiconductor laser, and FIG. 1b is a schematic diagram of its atomic arrangement. FIG. 2 is a sectional view of one embodiment of the present invention.
FIG. 3a is an energy band diagram near the active layer of an embodiment of the present invention, and FIG. 3b is a schematic diagram of its atomic arrangement. In the figure, 1 is an n-type carrier confinement layer, 2 is an active layer, 3 is a P-type carrier confinement layer, and 4 is an n-type
AlAs layer, 5 is P-type AlAs layer, 6 is n-GaAs substrate,
7 is a buffer layer, 8 is an n-type cladding layer, 9 is a P
type cladding layer, 10 is the cap layer, 11 is SiO ₂
12 is a P-type electrode, 13 is an N-type electrode, and 14 is an electrode window.

Claims (1)

[Claims] 1. an active layer, first and second semiconductor layers sandwiching the active layer above and below and comprising a compound semiconductor made of two elements and having a larger forbidden band width than the active layer; and the first and second semiconductor layers. and third and fourth semiconductor layers sandwiching a quantum well type three-layer structure consisting of the active layer above and below, having a larger forbidden band width than the active layer, and made of a compound semiconductor made of at least three or more elements. A semiconductor laser comprising: the first and second semiconductor layers each having a thickness such that electrons and holes can pass therethrough by a quantum mechanical tunneling phenomenon.