JPS6320395B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to semiconductor lasers, and more particularly to improvements in buried structure semiconductor lasers.

Figure 1 shows a conventional current confinement type mesa substrate buried structure laser, which is a type of buried structure semiconductor laser.
Current Confinement Mesa Substrate Buried
Heterostructure Laser DiodeCCM−
LD: References, Institute of Electronics and Communication Engineers Photon Quantum Electronics Study Group materials OQE80-117) are shown. CCM−
The LD has an active layer 4a (InGaAsP, λg~1.3μ
m), active layers 4b on both sides of the striped projections 2;
(InGaAsP, λg ~ 1.3 μm) is formed with interruptions, so that the active layer 4a includes the buffer layer 3 (n.InP) with a small refractive index and the first cladding layer (p.
It has a so-called embedded structure, surrounded by Inp). Also, current blocking layer 6 (n.InP)
is missing on the striped protrusion 2 and is formed only on both sides thereof, so that current can be efficiently concentrated in the active layer 4a.

This CCM-LD result is formed using the sliding method, which is a type of liquid phase growth method. In this liquid phase growth, when forming the first cladding layer 5 and the current blocking layer 6 after forming the active layers 4a and 4b, since the active layer 4a is on the striped protrusion 2, it protrudes more than other regions. It has the disadvantage that it easily comes into contact with the carbon boat for liquid phase growth, and as a result, it is susceptible to mechanical damage, resulting in crystal breakage and the generation of dislocations. CCM-LDs made from such mechanically damaged crystals had a high rate of deterioration when energized and had a short lifespan.

An object of the present invention is to provide a semiconductor laser whose active layer is less susceptible to the above-mentioned mechanical damage and has a long life.

According to the present invention, a semiconductor substrate having at least three mutually parallel stripe-like protrusions, an active layer formed on the semiconductor substrate, and a current blocking layer having a defect in at least one of the stripe-like protrusions are provided. A semiconductor laser characterized by the following features is obtained.

The present invention will be described in detail below with reference to the drawings.
FIG. 2 is a sectional view of one embodiment of the present invention. In the figure, 11 is an n-InP substrate, 12, 13, 14 are striped projections, 15 is a flat part, 16 is a buffer layer (n-InP, thickness ~0.5 μm), 17a, b, c, d
is the active layer (InGaAsP, λg ~ 1.3 μm, thickness ~
0.2μm), 18 is the first cladding layer (P/InP, thickness
0.7 μm), 19 is a current blocking layer (n InP, thickness ~
0.7 μm), 20 is the second cladding layer (p-InP, thickness 2-5 μm), 21 is the cap layer (p-InGaAsP,
λg ~ 1.3 μm, thickness ~ 1 μm), 22 is the p electrode, 2
3 is an n-electrode. The main light emitting region of the buried structure laser of this embodiment is the active layer 17a formed on the striped protrusion 12. Since the active layer 17 is formed with a step break at the step, the active layers 17a, 17b, 17c, and 17d are each discontinuous. Furthermore, since the current blocking layer is missing on the active layer 17a, current is intensively injected into the active layer 17a. Striped projection 12
The width of the upper side is about 2 μm, the height is about 3 μm, the interval between the striped upper protrusions 12 and 13 and the interval between the striped protrusions 12 and 14 is 5 to 20 μm, the width of the upper side of the striped protrusions 13 and 14 is 20 to 50 μm, The height is about 3 μm, and the width of the flat portion 15 is 100 to 150 μm.

Now, in conventional CCM-LDs, the light-emitting region protrudes more than other regions, which has the disadvantage of being susceptible to mechanical damage during crystal growth. However, in the semiconductor laser of this embodiment, since the three active layer regions of the active layer 17a and the active layers 17b and 17e on both sides thereof protrude beyond the flat portion 15, the active layer 17a which is the main light emitting region is in the liquid phase. The probability of mechanical damage due to contact with the growth carbon boat was significantly reduced.

The manufacturing method of the buried structure semiconductor laser of this example will be briefly described. First, three stripe-shaped protrusions 12, 13, and 14 are formed along the <011> crystal orientation on an n.InP substrate 11 whose main surface is the (100) plane by photoetching. Next, by a kind of sliding method of liquid phase growth method, the buffer layer 16, the active layers 17a, b, c, d, the first cladding layer 18, the current blocking layer 19, and the second cladding layer 2 are formed.
0, the cap layer 21 is successively grown. At this time, by controlling the degree of supercooling of the liquid phase growth solution, the buffer layer 15 and the first cladding layer 18 grow on the striped projections 12, but the current blocking layer 19 is cut off on the striped projections 12. and grow. Further, the current blocking layer 19 grows on the striped projections 13 and 14 because its width is wider than that of the striped projection 12. or,
The active layers 17a, b, c, and d made of InGaAsP do not grow on the side surfaces of the striped projections 12, but are formed with steps. After polishing the laser crystal thus obtained to a thickness of about 100 μm, a p-electrode 22 is formed on the cap layer 21 and an n-electrode 23 is formed on the n-InP substrate 11 by vacuum evaporation, followed by heat treatment. Make ohmic contact between the electrodes. Thereafter, a buried structure semiconductor laser is obtained by cutting out a cavity with a length of about 200 to 300 μm.

In this embodiment, the current blocking layer 19 is grown by cutting it on the striped projections 12 during crystal growth to form a current path. After forming the current blocking layer 19 by liquid phase growth, a p-type impurity such as Zn or Cd is selectively introduced into the vicinity of the striped protrusions 12 by diffusion or ion implantation.
A current path may be formed by inverting the conductivity type from n type to p type. Further, in this embodiment, the stripe-like protrusions include three stripe-like protrusions, the stripe-like protrusion 12 in the main light emitting region and the stripe-like protrusions 13 and 14 on both sides of the stripe-like protrusion 12, but the stripe-like protrusion 1 is not limited to this.
Three or more items similar to 3 and 14 may be provided.

Finally, to summarize the features of the present invention, the active layer is less susceptible to mechanical damage during crystal growth, and therefore a long-life buried structure semiconductor laser can be obtained with a high yield.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a current constriction type mesa substrate embedded laser (CCM-LD). FIG. 2 is a sectional view of a buried structure semiconductor laser according to an embodiment of the present invention. In the figure, 1... n.InP substrate, 2... striped protrusion, 3... buffer layer, 4a, 4b... active layer, 5... first cladding layer, 6... current blocking layer, 7... 2nd cladding layer, 8...cap layer,
9...p electrode, 10...n electrode, 11...n・
InP substrate, 12, 13, 14...stripe-like projections, 15...flat portion, 16...buffer layer, 1
7a, 17b, 17c, 17d are active layers, 18...
...First cladding layer, 19... Current blocking layer, 20...
...Second cladding layer, 21...Cap layer, 22...
. . . p electrode, 23 . . . n electrode.

Claims (1)

[Claims] 1. first and second striped protrusions parallel to each other, and a space between the first and second striped protrusions that is parallel to these protrusions and narrower than the width of the first and second striped protrusions. a semiconductor substrate on which a third stripe-shaped projection having a width is formed;
an active layer formed on the semiconductor substrate discontinuously between the first to third striped protrusions and valleys of the striped protrusions; a cladding layer covering the active layer; and a cladding layer disposed on the cladding layer. and a current blocking layer formed on the third stripe-shaped protrusion except for the cladding layer, and a current is injected into the active layer on the third stripe-shaped protrusion to cause the active layer to emit light. semiconductor laser.