JPH0552676B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a semiconductor laser that oscillates in a stable single transverse mode with a low threshold value.

(Prior Art) Generally, it is important for a semiconductor laser to oscillate in a single transverse mode stably with a low threshold value as a light source for optical communication and optical information processing. Conventionally, when manufacturing semiconductor lasers, the mainstream was to grow semiconductor laser crystals by liquid phase epitaxial growth (hereinafter referred to as LPE growth), but metal organic decomposition method (hereinafter referred to as LPE growth) was the mainstream.
Crystal growth using MOCVD (MOCVD) is attracting attention from the viewpoint of uniformity and mass productivity.

FIG. 1a is a cross-sectional view showing the stacked state of the active layer of a semiconductor laser fabricated by LPE growth on a substrate having a V-groove. First, a current blocking layer 2 having a conductivity different from that of the substrate 1 and having a smaller forbidden band width than the active layer is formed on a semiconductor substrate 1, and a V-groove extending from this current blocking layer 2 to the semiconductor substrate 1 is provided. When the first cladding layer 3 and the active layer 4 are sequentially laminated by LPE growth on the substrate 1 having the V-groove, the first cladding layer 3 fills the V-groove flatly and the first cladding layer 3 flatly fills the V-groove. flat active layer 4 on layer 3
is grown as a crystal.

The active layer 4 on this V-groove is connected to the current blocking layer 2 or the first cladding layer 3 with respect to the semiconductor substrate 1.
Since it is separated from the active layer 4 formed on the flat part other than the V-groove through the V-groove, it forms an optical waveguide mechanism and provides an excellent semiconductor laser that stably oscillates in a single transverse mode. . However, certain mixed crystal systems, e.g.
AlGaInP mixed crystal systems on GaAs substrates are extremely difficult to grow by LPE, and can only be produced by non-equilibrium growth methods such as MOCVD.

On the other hand, when manufacturing this semiconductor laser by the MOCVD method, this MOCVD method has the advantage of uniformity and mass production, but as shown in Figure 1b, the V-groove shape is left as it is on the V-groove. A first cladding layer 3 and an active layer 4 are grown;
There is a drawback that it is not possible to obtain the active layer shape as shown in Figure a.

(Objective of the Invention) The object of the present invention is to provide a semiconductor laser which eliminates the above-mentioned drawbacks and allows a structure having a V-shaped waveguide mechanism and a current blocking layer to be easily manufactured by the MOCVD method. be.

(Structure of the Invention) The structure of the present invention is a semiconductor laser having a double heterostructure semiconductor layer in which an active layer is sandwiched between first and second cladding layers. a mesa provided including a large first semiconductor layer; and a second semiconductor that covers other than the upper surface of the mesa and the upper surface of the substrate, has a band gap smaller than that of the active layer, and has a different conductivity from the semiconductor substrate. layer, and the double heterostructure semiconductor layer is provided on top of the second semiconductor layer.

According to the configuration of the present invention, the active layer on the upper part of the mesa, which has a second semiconductor layer on the side surface which has a smaller bandgap than the active layer and has a different conductivity from the semiconductor substrate, has a waveguide mechanism, and the second semiconductor layer has a waveguide mechanism. Since the conductivity of the layer is different from that of the semiconductor substrate, current is effectively injected into the light-emitting region of the active layer and oscillates, and since it can be manufactured without using the specificity of LPE growth, it is manufactured by MOCVD method and photolithography. be able to.

(Example of the invention) The present invention will be explained in detail below using the drawings.

FIG. 2 is a cross-sectional view of an embodiment of the invention. In this embodiment, a mesa 20 including a first semiconductor layer 11 having a larger forbidden band width than an active layer 4 is provided on a semiconductor substrate 1 . On both sides of this mesa 20 are active layers 4.
A second semiconductor layer 12 having a smaller forbidden band width and different conductivity from the semiconductor substrate 1 is provided.
Above the mesa 20 and the second semiconductor layer 12,
A double heterostructure consisting of a first cladding layer 3, an active layer 4 and a second cladding layer 5 is provided. The central part of the flat active layer 4 above this mesa 20 is in contact with the first semiconductor layer 11 via the first cladding layer 3, and both ends thereof absorb light via the first cladding layer 3. It is in contact with a second semiconductor layer 12 whose forbidden band width is smaller than that of the active layer 4 . Therefore, the active layer 4 above the mesa 20 has a light waveguide mechanism, and current is effectively injected into the center of the active layer 4 above the mesa 20 by the second semiconductor layer 12. Therefore, a semiconductor laser having this structure oscillates in a stable single transverse mode with a low threshold value.

3A to 3E are sectional views specifically showing the embodiment of FIG. 2 in the order of manufacturing steps. First, the third
As shown in Figure a, a p-type Al _0.3 Ga _0.7 As semiconductor layer, which will become the first semiconductor layer 11, is formed on a p-type GaAs substrate 1.
The width of SiO 2 is grown by MOCVD method, and the width of SiO ₂ is grown on the surface by photolithography and chemical etching.
3 μm stripes 30 are formed. next,
It was inserted into a MOCVD furnace, and HCl and AsH ₃ were poured in to heat and etch it (Fig. 3b). After that, an organic metal serving as a growth source, AsH ₃ , and a dopant gas were sent to grow n-type GaAs to a thickness of 0.7 μm. , a second semiconductor layer 12 is formed (FIG. 3c). Afterwards, the SiO ₂ stripe 30 is removed by chemical etching (Fig. 3 d), and after appropriate pretreatment, the SiO 2 stripe 30 is removed again.
Using the MOCVD method, a p-type Al _0.3 Ga _0.7 As layer with a thickness of 0.3 μm becomes the first cladding layer 3, a non-doped GaAs layer with a thickness of 0.1 μm becomes the active layer 4, and an n-type Al _0.3 Ga _0.7 layer becomes the second cladding layer 5. Laminate an As layer of 1.5μm (third
Figure e). Furthermore, an n-type GaAs layer is actually grown on the second cladding layer 5. The wafer thus produced is used to form a semiconductor laser through a normal device forming process.

(Effect of the invention) Since the active layer 4 of this semiconductor laser is a GaAs layer and the second semiconductor layer 12 is also a GaAs layer, the mesa 2
Since a waveguide mechanism is formed in the active layer 4 above the 0, stable single transverse mode oscillation is possible.

In addition, in manufacturing the semiconductor laser of this example, the SiO ₂ stripe 30 was removed from the state shown in FIG. Due to the difference in etching rate between the upper and lower parts of the mesa in chemical etching, GaAs is etched and the third
Another method is to create the structure shown in Figure d. moreover,
When the forbidden band width of the semiconductor substrate 1 is larger than that of the semiconductor layer that will become the active layer 4, the first semiconductor layer 11 may not be laminated and the semiconductor substrate 1 may be used instead.

[Brief explanation of the drawing]

Figures 1a and b show LPE and grooved substrates.
A cross-sectional view showing how lamination is performed by MOCVD,
Figure 2 is a schematic cross-sectional view of an embodiment of the present invention, Figure 3a
-E are sectional views showing FIG. 2 in the order of manufacturing steps. In the figure: 1...Semiconductor substrate, 2...Current blocking layer, 3
...first cladding layer, 4...active layer, 5...second cladding layer, 11...first semiconductor layer, 12
... second semiconductor layer, 20 ... mesa, 30 ...
SiO ₂ stripes.

Claims (1)

[Claims] 1. In a semiconductor laser having a double heterostructure semiconductor layer in which an active layer is sandwiched between first and second cladding layers, a first semiconductor layer having a band gap larger than that of the active layer is provided on a semiconductor substrate. a second semiconductor layer that covers side surfaces other than the upper surface of the mesa and the upper surface of the substrate, has a narrower band gap than the active layer, and has a different conductivity from the semiconductor substrate; A semiconductor laser characterized in that the double heterostructure semiconductor layer is provided on top of the semiconductor layer.