JPS6292388A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To stabilize the longitudinal mode of a GaAlAs/GaAs group semiconductor laser element by forming superlattice structure onto a substrate. to which a diffraction grating is shaped, under constant conditions and continuously forming an active layer to the superlattice structure. CONSTITUTION:A first clad layer 2, an optical guide layer 3 having a superlattice structure consisting of at least two semiconductor films having different compositions, a GaAs active layer 4, a second clad layer 5 and a cap layer 6 are successively formed onto an N-GaAs substrate 1 to which a diffraction grating 20 is shaped where nc<ng<na holds in the equivalent refractive index ng of the layer 3, the refractive index nc of the layer 2 and the refractive index nq of the layer 4. An insulating layer 7 is formed onto the layer 6, and the layer 7 is removed in a striped manner in order to limit a light- emitting region. Electrodes 8, 9 are shaped, thus acquiring a semiconductor laser element.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to the structure of a semiconductor laser probe having a longitudinal mode stabilization mechanism that can be manufactured using molecular beam epitaxy (MBE).

<Prior Art> In recent years, the fields of application of semiconductor laser probes, such as compact disc players, video disc players, and optical disc files, have been rapidly expanding. In order for these applied devices to demonstrate their high performance and functionality, semiconductor laser devices must ensure stable optical properties.
Therefore, semiconductor laser elements applied to these devices are equipped with a refractive index waveguide mechanism. In fact, due to this refractive index waveguide mechanism, the drawing mode of the F conductor laser element is highly stabilized, and it has reached the point where it has characteristics similar to j, :1-f- compared to the 17th device. However, other applied equipment,
For example, many laser beam printers and laser-applied measuring instruments require high stability not only in the transverse mode of the semiconductor laser element but also in its longitudinal mode. Distributed feedback structures called DFB and DBR have been proposed for stabilizing the longitudinal mode, and intensive research is being conducted on InGaAsP/TnP systems for use in optical communications.

However, in GaA, i:As/GaAs materials, A,
The surface of the region containing 9 is easily oxidized, and therefore, the GaA that formed the diffraction grating is interrupted for the formation of the diffraction grating.
There is a problem that regrowth on 4As is difficult, so it has not been put into practical use.

That is, in order to fabricate a distributed feedback type semiconductor laser probe, for example, a liquid phase growth method is usually used, and after the first cladding layer is grown, a diffraction grating for creating a distributed feedback mechanism is formed on the crystal surface. The first cladding layer, the active layer, and the second cladding layer are grown again, or after the first cladding layer, the active layer, and the second cladding layer are grown, a diffraction grating is formed and the second cladding layer is grown again. In order to form a diffraction grating, it is necessary to interrupt the crystal growth, such as growing a diffraction grating, and this makes it difficult to re-grow the layer on which the diffraction grating was formed. This is one of the major reasons why semiconductor laser devices have not been put into practical use.

<Object of the Invention> In view of the above-mentioned circumstances, the present invention provides a GaAs/GaAs semiconductor laser device in which the longitudinal mode is stabilized by a distributed feedback type using molecular beam epitaxy as a crystal growth method. The purpose is to

<Structure of the Invention> Through various experiments, the present inventors have found that in the molecular beam epitaxy method, when a superlattice structure is formed under certain conditions on a substrate on which a diffraction grating is formed, an appropriate thickness can be obtained. We found that after growing a superlattice, the diffraction grating disappears on its surface, resulting in an almost flat surface.

The present invention utilizes this phenomenon, and the semiconductor laser device of the present invention is a GaAlAs/GaAs-based semiconductor laser device, which is formed by sequentially forming a cladding layer, a light guide layer, and a light guide layer on a semiconductor substrate on which a diffraction grating is formed.
The active layer and the second cladding layer are laminated by a molecular beam epitaxy method, and the optical guide layer is configured with a superlattice structure consisting of at least two semiconductor films having different compositions,
The equivalent refractive index of the light guide layer and the refractive indexes of the first cladding layer and the active layer are respectively n2. nc,
It is characterized in that, when na, nc<ng<na.

By doing this, there is no interruption in the growth of the semiconductor layer, so even in the GaA/As/GaAs system, a distributed feedback type semiconductor laser probe with a stable longitudinal mode can be obtained.

easily obtained.

<Example> FIG. 1 schematically shows an embodiment of the present invention.

n-GaAs substrate I on which a diffraction grating is formed
A4 As first cladding layer 2, Gag, 70.
7 0.3 A. , a light guide layer 3 having a superlattice structure composed of 3As and GaAs, a GaAs active layer 4, p-Ga0.65
A second cladding layer 5 of AZo, 35AS, and a p-GaAs cap layer 6 are formed in this order. The equivalent refractive index of the light guide layer 3 and the refractive indices of the first cladding layer 2 and the active layer 4 are ng, nc, and n, respectively.

When nc<ng<na.

By doing so, the light is effectively guided without loss.

On the p-GaAs cap layer 6, 5iO is formed as an insulating layer.
The p layer 7 is formed by a chemical vapor deposition method (CVD method), and in order to limit the light emitting region, this S I Ox layer 7 is removed in a stripe shape with a width of 3 μm. Furthermore, AuGa/N is used as an electrode on the n-GaAs substrate 1 side.
The i-electrode 8 is made of AuZn on the p-GaAs cap layer 6 side.
Electrode 9 is formed by a vapor deposition method.

Next, the manufacturing method for the semiconductor laser device of the embodiment shown in FIG. 1 will be explained in FIGS. 2(A), (B) to 7(A).
, (B).

FIGS. 2A and 2B show an n-GaAs substrate 1, on the surface of which diffraction gratings 2° are formed at a pitch of 3600 by using a two-beam interferometry method. This n-GaAs substrate 1 is introduced into a molecular beam epitaxy apparatus.
A L o 3A S first cladding layer 2 is formed to have a thickness of 1.5 μm. At this time, the diffraction grating 20 formed on the substrate 1 remains almost intact on its surface.
The state is as shown in FIG. Next, this first
The cladding layer 2 is made of GaO, 7Aji (not shown in FIG. 5).
jO,3As film 21 about 40 people and GaAs film 22 about 22 people
Approximately 15 minutes guide layer 3 is formed as shown in FIG. At this time, the growth rate is slightly different at the bottom and top of the diffraction grating, about 3
After the growth of 000 people, the grating structure almost disappears,
An almost flat surface as shown in FIG. 4 is obtained. As shown in FIG. 5, this light guide layer 3 is made of GaO. 7”
Flattening is achieved due to the superlattice structure of the 0.3ΔS film 21 and the GaAs film 22. Further, following this, Figure 6 (A
), as shown in (B), after forming a GaAs active layer 4 of 700 layers, a p"0.65A '0.35As second cladding layer 5 of 1 μm, and a p-GaAs cap layer 6 of 5000 layers, Take out from the molecular beam epitaxy apparatus.

The structure of the wafer at this time is as shown in FIGS. 6(A) and 6(B). Next, 3,000 layers of 5jOv layer 7 are formed on the cap layer 6 by CVD, and then removed in stripes with a width of 3 μm by photolithography.

Finally, an n-side electrode 8 and a p-side electrode 9 are formed by vapor deposition,
Divide into individual elements by cleavage method.

In the semiconductor laser probe manufactured in this way, the forbidden band width and refractive index ng of the optical guide layer 3 having a superlattice structure are
are two semiconductor films 21 with different compositions forming a superlattice.
．． Appropriate values can be obtained by selecting the composition and film thickness of 22. Therefore, the above formula n. <ng
<Ha can be satisfied.

In the above example, oscillation was obtained at a threshold current of 150 mA, and the longitudinal mode was maintained at the same longitudinal mode up to an optical output of 5 mW or more. Furthermore, the longitudinal mode is extremely stable against temperature changes; when the drive current is fixed at 230 mA, no mode pops are observed from 15°C to 50°C, and the rate of change in the oscillation wavelength during this period is 0.65. A very small value of person/deg was obtained.

FIG. 8 shows another embodiment of the present invention. In this embodiment, in addition to stabilizing the longitudinal mode, which is the gist of the present invention, the first cladding layer 106 and the third cladding layer 108 are With the n-GaAs current confinement layer 107 provided in between,
In addition to constricting the current in a stripe pattern, stabilization of the transverse mode is also achieved due to the light absorption effect, thereby realizing a semiconductor laser device that is extremely stable in both the longitudinal mode and the transverse mode.

In FIG. 8, 101 is an n-electrode, +02 is an n-GaAs substrate, 103 is a first cladding layer, 104 is a superlattice optical guide layer, 105 is an active layer, 109 is a p-cap layer, 110 is the p-electrode.

<Effects of the Invention> As is clear from the above, according to the present invention, the longitudinal mode is stable, there is no need to interrupt growth when forming a diffraction grating, and the active layer is continuous with the superlattice layer. By being formed as a superlattice buffer layer, it is possible to obtain an effect as a superlattice buffer layer, and to obtain a semiconductor laser device having a light emitting region made of a group of high-quality crystal layers.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of one embodiment of the present invention, and FIG. 2 (A). (B) is a side view and front view of the substrate on which the diffraction grating is formed, Figures 3 (A) and (B) are side views and front views of the state where the first cladding layer has been grown, Figure 4 (A), (B) is a side view and a front view of the state in which the light guide layer has grown, FIG. 5 is a schematic structural diagram of the light guide layer, and FIGS. 6 (A) and (B) are side views of the state in which it has grown to the cap layer. and front view, Fig. 7 (A), (B)
8 is a side view and a front view of a state in which device formation is completed, and FIG. 8 is a schematic % formula of another embodiment of the present invention. 3...Light guide layer, 4...GaAs active layer, 5...' I) Gao. 65A zO. 35A
s second cladding layer, 6... p-GaAs cap layer, 101-n-electrode, 102- n-GaAs substrate, 103... first cladding layer, 104... superlattice optical guide layer, 105.・Active layer, 106・2nd
Cladding layer, 107-GaAs current confinement layer, 108...Third cladding layer, 109...p-gap layer, 110p-electrode. Patent applicant: Sharp Corporation Agent
Patent attorney Previously mentioned 2 famous confections 1 Fig.

Claims (2)

[Claims] (1) A GaAlAs/GaAs-based semiconductor laser device in which at least a first cladding layer, an optical guide layer, an active layer, and a second cladding layer are sequentially deposited on a semiconductor substrate by molecular beam epitaxy, is formed of a superlattice structure in which a diffraction grating is formed, and the light guide layer is composed of at least two semiconductor films having different compositions, and the equivalent refractive index of the light guide layer, the first cladding layer, and the The refractive index of the active layer is n_
A semiconductor laser device characterized in that when g, n_c, and n_a, n_c<n_g<n_a. (2) In the superlattice structure forming the optical guide layer, at least one of the plurality of semiconductor films having different compositions forming the superlattice structure has a thickness of 100 Å or less. A semiconductor laser device according to claim 1.