JPH0552677B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The semiconductor laser of the present invention relates to a high-output semiconductor laser that oscillates in a stable single transverse mode.

(Prior art and its problems) Semiconductor lasers are important for stable single transverse mode oscillation and high output as light sources for optical communications and optical information processing. Currently, semiconductor lasers often employ a structure called a buried structure (hereinafter abbreviated as BH structure) in which an active layer is embedded in a semiconductor layer whose refractive index is lower than that of the active layer. However, when the width of the buried active layer exceeds 2 μm, the transverse higher-order mode easily oscillates. Furthermore, even if single transverse mode oscillation occurs at a low injection level, there is a problem in that single transverse mode oscillation cannot be maintained if a high carrier is injected to achieve high output operation.

(Object of the Invention) An object of the present invention is to provide a high-output semiconductor laser that oscillates in a stable single transverse mode, eliminating the above-mentioned problems.

(Structure of the Invention) The structure of the semiconductor laser of the present invention is such that at least both sides of a first semiconductor layer in a mesa stripe shape having a refractive index smaller than that of the active layer are covered with a second semiconductor layer having a smaller refractive index than the first semiconductor layer. It is characterized in that it has a double heterostructure including a mesa having a sandwiched structure and an active layer bent above the mesa and on both sides of the mesa.

(Operations and Effects of the Invention) According to the configuration of the present invention, the active layer above the mesa is 1
form two optical waveguides. Furthermore, inside the active layer that forms the optical waveguide at the top of the mesa, the refractive index of the semiconductor layer that forms the mesa increases at the center, so the refractive index at the center is equivalently high. There is. This makes it possible to maintain a single transverse mode even when the optical waveguide width determined by the mesa width is widened and the optical waveguide cross section is increased to increase output.

(Detailed description of the configuration) A detailed description will be given below using the drawings. FIG. 1 shows a schematic cross-sectional view (FIG. 1b) and a refractive index distribution (FIG. 1a) of the semiconductor laser of the present invention. The mesa 100 has a structure in which a first semiconductor layer 30 having a higher refractive index than the active layer 4 is sandwiched between second semiconductor layers 20 having a lower refractive index than the first semiconductor layer 30. An active layer 4 is located along the mesa 100 with the first cladding layer 3 interposed therebetween. At this time, the active layer 4 has a bent shape, and the active layer above the mesa forms an optical waveguide. Furthermore, an equivalent refractive index difference is formed between the center portion A and the end portions B inside the active layer in the upper part of the mesa. The equivalent refractive index of the active layer in part A is larger than the equivalent refractive index of the active layer in part B because the refractive index of the first semiconductor layer included in the mesa is larger than the refractive index of the second semiconductor layer. Become. The state of the refractive index is shown in Figure 1a.
That is, it is an equivalent refractive index distribution in the lateral direction of E-L in FIG. The difference in refractive index between the central part and the end part is usually sufficiently small compared to BH, and the light is guided with a width _of W ₁ and the refractive index of the central part is high. Even if the width is increased, the single horizontal position is maintained. Simply put, the optical waveguide formed by the active layer has an equivalent radio optical cavity structure. FIG. 2 shows an example of a modification of the semiconductor laser of the present invention, in which a first cladding layer 40 and an active layer 4 having a smaller refractive index than the active layer 4 on the upper mesa and a larger refractive index than the first semiconductor layer 30 are shown in FIG.
It has a double hetero horizontal structure sandwiched between waveguide layers 50 which have a smaller refractive index and a larger refractive index than the second cladding layer 5.

(Example) The following will be explained using examples. The laser of the present invention was manufactured as follows. FIG. 3 is a manufacturing process diagram of the semiconductor laser of the present invention, in which p-type Al _0.2 which becomes the first semiconductor layer 30 is placed on the p-type GaAs substrate 1.
The Ga _0.8 As layer was deposited using a 1 μm organometallic decomposition method (hereinafter referred to as MOCVD).
(abbreviated as law), as shown in Figure 3 a.
After forming the SiO ₂ stripe mask 200
Gas phase etching is performed inside the MOCVD reactor tube (Fig. 3b), and then the n
An Al _0.3 Ga _0.7 As layer was grown to produce the shape shown in Figure 3c. Thereafter, SiO ₂ was removed (Fig. 3d), and after etching treatment, a p-type Al _0.2 Ga _0.8 As layer, which would become the first cladding layer 3, was deposited with a thickness of 0.3 μm using the MOCVD method. GaAs layer
0.1 μm, Al _0.3 Ga _0.8 As, which becomes the second cladding layer 5
A layer of 2 .mu.m thick was grown to produce the laser structure of the present invention shown in FIG. 3e. In reality, a GaAs cap layer is grown on top of it. At this time, the second semiconductor layer 2
0 has a different conductivity from the semiconductor substrate 1, so a pn-pn structure is formed in areas other than the center of the mesa, and current is injected only into the light emitting region of the active layer. As described above, the semiconductor laser of the present invention is a high-output semiconductor laser that oscillates in a stable single transverse mode.

[Brief explanation of the drawing]

FIGS. 1a and 1b show a schematic cross-sectional view and refractive index distribution of the semiconductor laser of the present invention, FIG. 2 is an example of a modification of the laser of the present invention, and FIGS. 3a to 3e are manufacturing process diagrams. In the figure, 1 is a semiconductor substrate, 3 and 40 are first cladding layers, 4 is an active layer, 5 is a second cladding layer, 2
0... is the second semiconductor layer, 30 is the first semiconductor layer, 100 is the mesa, 50 is the waveguide layer, 200 is the
SiO ₂ stripes.

Claims (1)

[Claims] 1. A mesa having a structure in which both sides of a mesa-stripe-shaped first semiconductor layer having a refractive index lower than that of the active layer are sandwiched between second semiconductor layers having a lower refractive index than the first semiconductor layer, and A semiconductor laser characterized by having a double heterostructure including an active layer bent over the top of a mesa and on both sides of the mesa.