JP2855934B2 - Surface emitting semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical cavity surface emitting semiconductor laser used for highly parallel optical transmission and optical information processing.

[0002]

2. Description of the Related Art A conventional surface-emitting semiconductor laser has a problem that element resistance is high because an injection current passes through a mesa portion. Therefore, as shown in FIG. 4, a two-stage mesa-type surface emitting semiconductor laser was developed in which the upper dielectric multilayer mirror was removed by etching and current was injected from the lateral direction of the active layer to reduce the resistance (FIG. 4). Abstract of Solid State Device Conference, 1991, IOT 4, pp. 37-38).

[0003]

In the above-described conventional two-step mesa type surface emitting semiconductor laser, a dielectric multilayer film is stacked on a semiconductor multilayer film, and the dielectric layer is removed by etching in a mesa shape. Therefore, the manufacturing process is complicated, and since the etched surface coincides with the bottom surface of the second multilayer mirror, light confinement becomes weaker as the element size becomes smaller, and the oscillation threshold increases. there were.

An object of the present invention is to realize sufficient light confinement even in a small size by a simple manufacturing process while taking advantage of the low resistance of a two-stage mesa type surface emitting semiconductor laser device.

[0005]

According to a first aspect of the present invention, a first conductive type first multilayer mirror, a first conductive type first semiconductor layer, an active layer, A second semiconductor layer of the second conduction type, a second multilayer reflection mirror of the second conduction type is formed, and the surface emitting semiconductor laser emits laser oscillation light in a direction perpendicular to the growth surface. A second conductive type contact layer is formed in the multilayer reflector, and the periphery of the element is removed by etching to the contact layer to form an upper mesa, and the etched surface is formed from the bottom surface of the second multilayer reflector. Being underneath causes light to enter the upper mesa, creating a lateral refractive index profile and providing sufficient light confinement even in smaller mesas.

According to a second aspect of the present invention, in the surface emitting semiconductor laser according to the first aspect, the contact layer is located at an odd multiple of one-fourth of the wavelength in the medium from the active layer so that the contact layer has a large absorption coefficient. Is the position of the node of the standing wave of light,
This is to prevent the oscillation threshold from rising.

According to a third aspect of the present invention, in the surface emitting semiconductor laser according to the first aspect of the invention, the absorption coefficient is reduced by using a non-conductive type of the second multilayer mirror which is not related to the current injection, thereby reducing the oscillation threshold. Is to be reduced.

According to a fourth aspect of the present invention, there is provided a surface emitting semiconductor laser according to the first aspect of the invention, wherein concentric etching grooves having a spacing suitable for the lateral oscillation wavelength are carved on the etched surface to thereby obtain a laterally distributed reflection type refraction. The purpose is to provide a rate distribution so as to obtain sufficient lateral light confinement even with an active layer having a smaller size.

[0009]

The first aspect of the present invention aims to improve the confinement of light in the active layer by generating a lateral refractive index distribution by the mesa portion, which will be described in more detail. FIG. 3 shows an N-type AlAs / GaAs multilayer reflector on a semiconductor substrate, an N-type Al _0.25 Gs _0.75 As, an In _0.2 Ga _0.8 As active layer,
P-type Al _0.25 Gs _0.75 As, P-type AlAs / GaAs
The dependence of the light confinement coefficient on the diameter of the upper mesa when the depth d from the etched surface to the upper portion of the active layer is a parameter in a structure in which s multilayer mirrors are sequentially formed is shown. d
= 1000,2000 °, almost sufficient light confinement is obtained, while d = 3,000,4000 ° is insufficient. In addition, in the situation where d = 6000 ° or more, that is, when the lower part of the second multilayer film reflecting mirror is included in the lower mesa, it is understood that there is almost no light confinement due to the refractive index waveguide. This is because when the multilayer film mirror has a high reflectivity and the multilayer film remains on the upper mesa, light does not seep into the upper mesa, and as a result, there is no lateral refractive index distribution. Therefore, as the distance between the second multilayer mirror and the contact layer (the mesa guide layer 2 in FIG. 1) becomes wider, the light confinement becomes stronger.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a structural sectional view showing an embodiment of the surface emitting semiconductor laser according to the first aspect of the present invention. On a semi-insulating GaAs substrate 11, an N-type multilayer film reflecting mirror 10 (λ / 4
It consists of 15 thick GaAs / AlAs pairs. ), N-type Al _0.25 Gs _0.75 As for the cladding layer 8, non-doped In _0.2 Ga _0.8 As (the thickness of 300 °) for the active layer 7;
P-type Al _0.25 Gs _0.75 As to the cladding layer 5, a contact layer 4 to become P-type GaAs, a Mesagaido layer 2 P-type Al _0.25 Gs _0.75 As, a second P-type multilayer reflector 1 ( GaAs / AlAs 15 pairs having a thickness of λ / 4) are sequentially grown by MBE. Next, the upper surface of the first multilayer film reflecting mirror 10 is removed by etching, and the contact layer 4 is further removed to a smaller size by etching. Then, on each etched surface, Au
An electrode 9 made of Ge-Ni and an electrode 3 made of Cr / Au are formed by vapor deposition. The total thickness of the mesa guide layer 2, the contact layer 4, and the cladding layer 5 is 2λ, the thickness of the cladding layer 8 is λ, and the distance from the active layer to the contact layer is 2000 °. Here, λ is the oscillation wavelength in the medium and is 9800 ° in a vacuum. Both sides of the active layer 7 are formed as high-resistance region layers 6 by hydrogen ion implantation. Even when the size of the first mesa is reduced to 3 μm, the light confinement coefficient of this element is reduced to only about 80% of the value when the element diameter is sufficiently large.

Further, the distance between the active layer and the contact layer is 2200 ° (5/4 of the oscillation wavelength in the medium).
At times, the contact layer is located at the node of the optical standing wave. ), The oscillation threshold can be reduced to about 90% of the case where the contact layer is at the position of the antinode of the optical standing wave.

Further, by undoping the second multilayer reflector, the oscillation threshold value can be set to be lower than that in the case where the multilayer reflector is doped and of a conduction type.
Further, it can be reduced to about 90%.

FIG. 2 is a structural sectional view showing an embodiment of the surface emitting semiconductor laser according to the present invention. Figure 1 shows the layer structure
Is the same as After etching in the same manner as in FIG. 1, a groove is further concentrically carved from the upper surface of the contact layer 4 by etching. On this, the electrode 9 is formed on the electrode 3 and the first multilayer mirror 10 as in FIG. The concentric grooves further enhance lateral light confinement. The pitch of the grooves should be half the wavelength in the transverse medium of the oscillation. For example, if the size of the upper mesa is 1 μm, the wavelength in the lateral medium is about 1 μm, so the pitch of the grooves is 0.5 μm.

Although the GaAs-based embodiment has been described above, the present invention is applicable to other material-based semiconductors such as an InP-based semiconductor.

[0015]

According to the present invention, a low oscillation threshold and a low resistance can be realized only by changing a simple layer structure using a technique for manufacturing a vertical cavity surface emitting semiconductor laser.

[Brief description of the drawings]

FIG. 1 is a structural sectional view of a surface emitting semiconductor laser for explaining an embodiment of the first, second and third inventions.

FIG. 2 is a structural sectional view of a surface emitting semiconductor laser for explaining an example of the fourth invention.

FIG. 3 is a diagram showing the dependence of the light confinement coefficient on the distance from the etched surface to the active layer in the surface emitting semiconductor laser of the present invention.

FIG. 4 is a structural sectional view of a two-stage mesa surface emitting semiconductor laser for explaining a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Second multilayer mirror 2 Mesa guide layer 3 Electrode 4 Contact layer 5 Cladding layer 6 High resistance layer 7 Active layer 8 Cladding layer 9 Electrode 10 First multilayer mirror 11 Substrate

Claims (4)

(57) [Claims] 1. A first conductive type first multilayer mirror, a first conductive type first semiconductor layer, an active layer, and a second conductive type second semiconductor layer on a semiconductor substrate. A surface emitting semiconductor laser in which a second multilayer mirror of the second conductivity type is formed and emits laser oscillation light in a direction perpendicular to the growth surface, wherein the second conductivity type is included in the second semiconductor layer. Of the contact layer, the periphery of the element is removed by etching to the contact layer,
A surface emitting semiconductor laser, wherein an etching surface is below a bottom surface of the second multilayer mirror. 2. The surface emitting semiconductor laser according to claim 1, wherein the contact layer is separated from the active layer by a quarter of the wavelength in the medium.
A surface emitting semiconductor laser, wherein the surface emitting semiconductor laser is located at a position which is an odd multiple of the above. 3. The surface emitting semiconductor laser according to claim 1, wherein the second multilayer reflector is undoped. 4. The surface emitting semiconductor laser according to claim 1, wherein concentric grooves are formed in the etched surface.