JPH0521899Y2 - - Google Patents

Description

[Detailed explanation of the idea] (b) Industrial application fields The present invention relates to a surface-emitting semiconductor laser.

(b) Conventional technology Figure 2 is a technical research report from the Institute of Electronics and Communication Engineers OQE84-
This type of laser is disclosed in No. 9.

In the figure, reference numeral 1 denotes a substrate made of n-type GaAs, and a buffer layer 2 made of n-type GaAs is laminated on one main surface side of the substrate, and the surface of the buffer layer 2 is layered from the other main surface of the substrate 1. A communication hole 3 for laser light output reaching . 4 is n type
This is a first cladding layer made of Ga0.6Al0.4As, and this cladding layer is laminated on the surface side of the buffer layer 2. Reference numeral 5 denotes an active layer made of P-type Ga0.9Al0.1As, and this active layer is laminated on the surface of the first cladding layer 4. 6 is a second layer made of P-type Ga0.6Al0.4As
This second cladding layer is laminated on the surface of the active layer 5. 7 is P type
This is a cap layer made of Ga0.85Al0.15As, and the cap layer is selectively laminated on the surface of the second cladding layer 6 directly below the communicating hole 3. 8 is for example SiO ₂
This insulating layer is laminated on the peripheral portion of the surface of the cap layer 7 and on the surface of the second cladding layer 6. 9 is the first layer consisting of three layers of Au-Zn-Au.
The first electrode is laminated on the surfaces of the cap layer 7 and the second cladding layer 6, and is in ohmic contact with the second cladding layer 6. 10 is
The Sn layer is laminated on the flat portion of the other principal surface of the substrate 1. Reference numeral 11 denotes an Au layer, which is laminated on the surface of the Sn layer 10, the inner wall of the communicating hole 2, and the surface of the first cladding layer 4 exposed by the communicating hole 2, and has a thickness of about 100 Å. Further, the Sn layer 10 and Au layer 11 on the flat portion serve as a second electrode that makes ohmic contact with the substrate 1.

In such a semiconductor laser, when a forward bias is applied between the first and second electrodes, the current is constricted by the contact portion 9a of the first electrode 9, and an active region 5a (in the figure) is formed directly under the communication hole 3 in the active layer 5. The shaded area) is generated. Further, since the contact portion 9a and the back surface of the Au layer 11 function as a reflecting mirror, laser oscillation occurs between the reflecting mirrors, and light is emitted in the direction of the arrow 12.

(c) Problems to be solved by the invention However, with such a configuration, it is not possible to confine light in the horizontal direction (direction perpendicular to the laser beam emission direction), so the light generated from the active region 5a is transmitted in all directions. It has spread. Therefore, the amount of light that travels back and forth between the reflecting mirrors and contributes to stimulated radiation is small. Therefore, there was a problem that the oscillation threshold current was high.

(d) Means for solving the problems The present invention was made in view of the above points, and its structural features include an active layer made of a material with a larger band gap energy than the active layer; In a surface-emitting type semiconductor laser having a pair of cladding layers sandwiching the layers, and a pair of reflecting mirrors disposed on the surfaces of both cladding layers so as to face each other, one of the cladding layers is connected to the reflecting mirror. a high refractive index layer laminated on the surface of the active layer facing the active layer, and a current confinement layer laminated on the surface of the active layer on which the high refractive index layer is not laminated, and whose layer thickness is smaller than that of the high refractive index layer. , and a low refractive index layer laminated on the current confinement layer, and the optical refractive index difference between the high refractive index layer and the low refractive index layer is 10 ^-3 or more.

(e) Effect In such a configuration, light generated in the active layer and directed toward the one cladding layer is concentrated in the portion where the optical refractive index is high.

(f) Example Figure 1 shows an example of the present invention, and 21 is an n-type
A substrate made of GaAs, 23 a first cladding layer made of n-type Ga0.6Al0.4As laminated on one main surface of the substrate, 23 laminated on the surface side of the cladding layer.
This is an active layer made of P ^- type Ga0.9Al0.1As. 24
is a communication hole for outputting laser light, and the communication hole is formed to a depth reaching the first cladding layer 22 from the other main surface of the substrate 21. 25 is about 100 Å thick
A first reflecting mirror made of an Au layer, which covers the first cladding layer 22 exposed through the communicating hole 24.
Laminated on the surface. 26 is a first electrode made of an Au-Sn alloy, and this electrode is formed on the other main surface of the substrate 21. 27 is carrier density 2×
This is a high refractive index layer made of P-type Ga0.6Al0.4As of 10 ¹⁸ cm ^-3 and is laminated on the surface of the active layer 23 facing the first reflecting mirror 25 . 28 is a current confinement layer made of n-type Ga0.6Al0.4As with a carrier concentration of 5×10 ¹⁷ cm ^-3 ; this layer is laminated on the surface of the active layer 23 on which the high refractive index layer 27 is not laminated; The layer thickness is thinner than the high refractive index layer 27. 29 is a low refractive index layer made of P-type Ga0.6Al0.4As with a carrier concentration of 7×10 ¹⁸ cm ^-3 , and this layer is laminated on the current confinement layer 28, and its surface is the same as the high refractive index 27 surface. Become the same plane. Furthermore, since the high refractive index layer 27, current confinement layer 28, and low refractive index layer 29 all have a larger energy band gap than the active layer 23, they act as a second cladding layer. 30 is 1000Å thick Au
This is a second reflecting mirror consisting of layers, and this reflecting mirror is laminated on the surface of the high refractive index layer 27. 31 is a second electrode made of Au-Zn alloy, and this electrode is connected to the low refractive index layer 2.
7.

In the device of this embodiment, when a forward bias is applied between the first electrode 26 and the second electrode 31, the current is constricted by the current confinement layer 28, and the current flows through the active layer 23 on the high refractive index layer 27 (hereinafter referred to as active region 32). Therefore, light is generated in the active region 32 due to the recombination of holes and electrons.

Such light normally has no directivity and therefore travels in all directions, but the light heading toward the second cladding layer has a refractive index of 3.33 for the high refractive index layer 27 and that of the low refractive index layer 29 (3.31). Since it is 0.02 higher than that, it is concentrated in the high refractive index layer 27. Further, the light concentrated on the high refractive index layer 27 is transferred to the first reflecting mirror 25 by the second reflecting mirror 30.
Thereafter, as shown by an arrow 33 in the figure, the light goes back and forth between the first and second reflecting mirrors 25 and 30 and contributes to the stimulated radiation.

In this way, in the device of this embodiment, the light generated from the active region 32 and directed toward the second cladding layer will then contribute to the stimulated radiation between the first and second reflecting mirrors 25 and 30, which is different from the conventional device. In comparison, more light contributes to stimulated radiation, and the oscillation threshold current also becomes lower.

In this example, regions with different optical refractive indexes were provided only in the second cladding layer, but the first cladding layer 27
By providing regions with different optical refractive indexes,
Furthermore, the oscillation threshold current of laser light can be reduced.

Further, in this embodiment, the difference in optical refractive index between the high refractive index layer 27 and the low refractive index layer 29 was set to 0.02;
It has been confirmed through experiments that light can be sufficiently focused on the high refractive index layer 27 if the value is 10 ^-5 or more.

(g) Effect of the invention According to the invention, one of the cladding layers includes a high refractive index layer laminated on the active layer surface facing the reflecting mirror, and a high refractive index layer laminated on the active layer surface on which the high refractive index layer is not laminated. The current confinement layer is laminated thereon and has a thickness smaller than the high refractive index layer, and the low refractive index layer is laminated on the current confinement layer, and the high refractive index layer and the low refractive index layer Since the optical refractive index difference is 10 ^-3 or more, it is possible to substantially confine light in the horizontal direction, and the oscillation threshold current of the laser beam can be reduced.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 is a sectional view showing a conventional example. 22...first cladding layer, 23...active layer, 2
5, 30...First and second reflecting mirrors, 27...High refractive index layer, 29...Low refractive index layer.

Claims (1)

[Scope of utility model registration request] an active layer, made of a material having a larger bandgap energy than the active layer, and sandwiching the active layer;
In a surface emitting type semiconductor laser having a pair of cladding layers and a pair of reflecting mirrors disposed opposite to each other on the surfaces of both cladding layers, one of the cladding layers is formed on the surface of the active layer facing the reflecting mirror. a current confinement layer laminated on the surface of the active layer on which the high refractive index layer is not laminated, and whose layer thickness is smaller than that of the high refractive index layer; 1. A surface-emitting semiconductor laser comprising laminated low refractive index layers, wherein the difference in optical refractive index between the high refractive index layer and the low refractive index layer is 10 ^-3 or more.