JPH0632338B2 - Embedded semiconductor laser - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an embedded semiconductor laser capable of oscillating in a stable single transverse mode and obtaining a high output.

(Prior art and its problems) Semiconductor lasers are used as light sources for optical communication and optical information processing. In such applications, semiconductor lasers oscillate in a stable single transverse mode and have high output. is important.

At present, as a semiconductor laser for these light sources, a structure having an active layer called a buried structure (hereinafter referred to as BH structure) embedded in a semiconductor layer having a smaller refractive index than the active layer is often adopted. However, the embedded semiconductor laser easily oscillates in a lateral higher-order mode when the width of the buried active layer is 2 μm or more, and at a low injection level, it operates at a high output even if a single lateral mode oscillates. However, there is a problem that single transverse mode oscillation cannot be maintained when carriers are highly injected.

An object of the present invention is to eliminate the above-mentioned problems and to provide an embedded semiconductor laser capable of oscillating in a stable single transverse mode and obtaining a high output.

(Means for Solving the Problems) In the embedded semiconductor laser of the present invention, the first semiconductor layer having a larger forbidden band width than the active layer is formed on the substrate by the second semiconductor layer having the same or smaller forbidden band width than the active layer. A mesa having a structure sandwiched by semiconductor layers is provided, and a double hetero structure having an active layer interrupted at an upper portion of the mesa and a lower portion of the mesa is provided on a substrate including the mesa. Therefore, since the active layer above the mesa is embedded in the semiconductor crystal having a smaller refractive index than the active layer, one light waveguide is formed. Further, in the active layer forming the optical waveguide above the mesa, the forbidden band width of the semiconductor forming the mesa is larger than the forbidden band width of the active layer in the center of the mesa and smaller on both sides of the mesa. Therefore, it has a double waveguide with another waveguide mechanism in the optical waveguide. As a result, the single lateral mode can be maintained even when the active layer width determined by the mesa width is widened and the cross-sectional area of the optical waveguide is increased to increase the output.

(Example) A detailed description will be given below with reference to the drawings.

FIG. 1 is a sectional view of an embodiment of the embedded semiconductor laser of the present invention, and the equivalent refractive index distribution of the waveguide mechanism is also shown in the upper part.

A mesa 100 is provided on a semiconductor substrate (P-type GaAs) 1. The mesa 100 has a forbidden band width larger than that of the active layer (GaAs) 4 and is a first semiconductor layer (P-type Al0.3Ga0.7As) 30.
Has a structure sandwiched by a second semiconductor layer (n-type GaAs) 20 having a band gap smaller than or equal to that of the active layer 4. The active layer 4 is located separately above and below the mesa 100. Therefore, the active layer 4 above the mesa is surrounded by the cladding layer 5 having a refractive index smaller than that of the active layer 4 to form one waveguide. is doing. The waveguide width is the first
W ₁ as shown in the figure. The active layer 4 on the mesa 100 is a thin clad layer (P-type Al0.3Ga0.7As) 3.
The portion A is in contact with the first semiconductor layer 30 and the portion B is in contact with the second semiconductor layer 20 via the. First semiconductor layer 30
Has a forbidden band width larger than that of the active layer 4, and the second semiconductor layer 20
Has a band gap smaller than or equal to that of the active layer 4. As a result, a waveguide mechanism having a width W _{2 is provided} inside the active layer 4 on the mesa. When the waveguide of the active layer 4 is replaced with the equivalent refractive index waveguide, the shape shown in the upper part of FIG. 1 is obtained. For example, IEE Journal of Quantum Electronics (IEEE)
Journal of Quantum Elect
ronics), Vol. QE-14, No. 2,89
~ The article "Transverse Mod" on page 94
e Stabilized AlxGai-xAs I
njection Lasers with Chan
nailed-Substrate-Planar St
Please refer to "ruture".

Light is guided by a waveguide having a width of W _{1
Due to} the existence of the waveguide having the width of _2, the single transverse mode is maintained even if the width of W ₁ is increased. Being able to widen the width of W ₁ means that a large output can be obtained, and it has a feature that the single transverse mode is maintained even at that time.

Hereinafter, a method of manufacturing the embedded semiconductor laser of the present invention will be described. 2 (a), (b), (c), and (d) are views showing the manufacturing process of the semiconductor laser of the present invention, and as shown in FIG.
Thickness of 1μ to be the first semiconductor layer 30 on the GaAs substrate
m P-type Al0.3Ga0.7As layer by metalorganic decomposition method (hereinafter M
After growth by OCVD method), a stripe mask 200 of SiO ₂ is formed as shown in FIG.
Vapor phase etching is performed inside the D furnace reaction tube, and then an n-type GaAs layer to be the second semiconductor layer 20 is grown to form the shape shown in FIG. Next, after removing SiO ₂ 200 and etching, a P-type Al0.3Ga0.7As layer to be the first cladding layer 3 is formed by liquid phase epitaxial growth to a thickness of 0.2 μm, and the active layer 4 is formed.
Figure 2 shows a non-doped GaAs layer 0.1μm thick and an n-type Al0.3Ga0.7As layer 2nd cladding layer 5 grown by 2μm.
A semiconductor laser structure of the present invention (d) was produced. Actually, a GaAs cap layer is further grown thereon, but it is not shown in the figure. Although the upper active layer 4 and the lower active layer 4 of the mesa 100 are separated from each other, such separate growth can be easily performed by liquid phase epitaxial growth.

(Effect of the Invention) As described above, in the present invention, since the active layer has the double waveguide mechanism, high output and single transverse mode oscillation can be easily obtained. In addition, since the second semiconductor layer has a different conductivity from the semiconductor substrate, a Pn-Pn structure is formed except in the central portion of the mesa, and therefore only in the light emitting region of the active layer and in the transverse fundamental mode. The implantation is performed with the width of W ₂ shown in FIG. 1 which gives a large gain. This is also convenient in combination with the waveguide mechanism for oscillating a single transverse mode.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of an embedded semiconductor laser of the present invention, and FIGS. 2 (a), (b), (c) and (d) are manufacturing process diagrams of the semiconductor laser of the present invention. . In the figure, 1 ... Semiconductor substrate, 3, 5 ... Clad layer, 4 ...
... active layer, 20 ... second semiconductor layer, 30 ... first semiconductor layer, 200 ... SiO ₂ stripe.

Claims (1)

[Claims] 1. A structure in which a first semiconductor layer having a forbidden band width larger than that of an active layer is sandwiched from a side surface on a semiconductor substrate by a second semiconductor layer having a band gap equal to or smaller than that of the active layer. An embedded semiconductor laser, wherein a mesa is provided, and a double hetero structure having an active layer interrupted at an upper portion of the mesa and a lower portion of the mesa is provided on a substrate including the mesa.