JPH08148755A - Plane emitting laser device and its manufacture - Google Patents

Abstract

PURPOSE: To provide a plane emitting laser device which allows the reduction of non-linearity (kink) of the light output/inrush current characteristics, its manufacture and a photomask to be used for it, since plane emitting laser devices permit the reflection light from the substrate rear side, from which light is taken, to re-inrush into the oscillator and cause kinks. CONSTITUTION: A p-type semiconductor multilayer film 3 and an n-type semiconductor multilayer film 7 compose a pair of reflection mirror for the laser resonator of a plane emitting laser oscillator. An active layer 5 is arranged between a pair of multilayer films. A laser oscillator 10, which has a pair of semiconductor multilayer films as a reflection mirror, is laminated on a semiconductor substrate 11 and the plane emitting laser is formed. On the rear side of the substrate, from which output light 14 is to be taken, a recessed structure 15 that has a reflection plane is provided.

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 laser device used for optical transmission and optical information processing, and in particular,
The present invention relates to a surface emitting laser device in which nonlinearity and instability of response due to returning light are reduced, a manufacturing method thereof, and a photomask used therefor.

[0002]

2. Description of the Related Art The structure of a conventional vertical cavity surface emitting laser device is described in, for example, Electronics Letters (Elctro).
n. Lett.), Vol. 25, No. 20, 1377-1989.
This is based on the surface emitting laser device described on page 1378.

A cross-sectional structure of a conventional vertical cavity surface emitting laser device is shown in FIG. This surface-emitting laser device is a surface-emitting device including an n-side electrode 8 connected to one end of a power supply 1 and a semiconductor laminated structure connected to the other end of the power supply 1 on the surface (upper side surface in the figure) of a semiconductor substrate 11. It has a laser oscillator 10 (hereinafter, simply referred to as a laser oscillator). As shown in the figure, the laser oscillator 10 sandwiches the active layer 5 with the cladding layers 4 and 6 to form a double hetero structure. The semiconductor layer including this double hetero structure is used as the intermediate layer 9 and the reflection mirror of the laser resonator is formed. An intermediate layer 9 is arranged between the constituent p-type semiconductor multilayer film 3 and the constituent n-type semiconductor multilayer film 7.

As described above, in the surface emitting laser device having the structure in which the laser oscillator 10 is mounted on the semiconductor substrate 11, the respective laminated surfaces are parallel to the substrate surface on the semiconductor substrate 11 and are sequentially stacked in the vertical direction. In this surface emitting laser device, the output light 14 is extracted from the back surface opposite to the surface on which the laser oscillator 10 is mounted.

[0005]

In the surface emitting laser device having such a structure, a part of the laser output light is reflected from the interface between the back surface of the substrate and the air and is again injected into the laser oscillator as return light. As a result, non-linearity (kink) in the optical output-injection current characteristics of the laser and fluctuations in the laser output due to noise and mode instability occur. In order to reduce this return light, it is necessary to apply an AR coat film to the back surface of the substrate, but it is not easy to sufficiently reduce the reflectance at the substrate-air interface.

Therefore, a technical object of the present invention is to provide a surface emitting laser device having a simple structure capable of reducing the return light to the laser oscillator, a manufacturing method thereof and a photomask used for the same.

[0007]

In order to solve the above problems, in a surface emitting laser device of the present invention, a semiconductor substrate having two front and back surfaces, and a semiconductor laminated layer formed on one surface of the semiconductor substrate are provided. In a surface emitting laser device comprising a structure and extracting laser light from the other surface of the semiconductor substrate facing the one surface, a structure for irregularly reflecting the laser light passing through the semiconductor substrate is provided on the other surface. It is characterized by having.

Here, in the present invention, it is preferable that the structure has a transmissive / reflecting surface that is not a parallel plane on one surface of the laminated semiconductor structure. Further, it is more preferable that the transmissive / reflecting surface is a concave surface formed on the semiconductor substrate or an inclined surface that intersects a plane parallel to the stacked one surface of the semiconductor layer structure.

The photomask of the present invention is a photomask for forming a structure on one surface of a semiconductor substrate by etching. The photomask is laminated on a glass substrate and one surface of the glass substrate. And a multilayer thin film layer for adjusting transmitted light, wherein the multilayer thin film layer has the number of layers corresponding to the pattern of the structure. Here, in the photomask of the present invention, it is preferable that the thin film is a reflective film that reflects light having a predetermined wavelength.

Further, according to the method of manufacturing a surface emitting laser device of the present invention, the semiconductor substrate having the semiconductor laminated structure forming the surface emitting laser oscillator is provided on the one surface of the semiconductor substrate having two front and back surfaces. Is a method of forming a structure that diffusely reflects the laser light that has passed through the semiconductor substrate on the other surface facing the other surface, wherein the structure is formed by etching the other surface.

[0011]

According to the present invention, in a surface emitting laser device in which a semiconductor laminated structure of a surface emitting laser oscillator is formed on one surface of a semiconductor substrate, the semiconductor laminated structure is formed on the other surface of the semiconductor substrate from which output light is extracted. A structure having a transmissive / reflecting surface that is not a plane parallel to the stacked one surface is provided. At this time, it is possible to prevent the reflected light from being re-injected into the laser oscillator as return light by diffusing the reflected light at the substrate-air interface by the structure.

By thus reducing the return light to the laser oscillator, it is possible to reduce the nonlinearity (kink) of the laser light output-injection current characteristic and the fluctuation of the laser output due to noise and mode instability. it can.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a conceptual sectional view showing a surface emitting laser device according to a first embodiment of the present invention. As shown in FIG. 1, the active layer 5 is sandwiched by the cladding layers 4 and 6 to form a double hetero structure. The intermediate layer 9 having this double hetero structure is arranged between the p-type semiconductor multilayer film 3 and the n-type semiconductor multilayer film 7 which form the reflecting mirror of the laser oscillator. A p-side electrode 2 is provided on the p-type semiconductor multilayer film 3. The semiconductor multi-layer structure composed of these layers 3 to 7 constitutes the surface-emission laser oscillator 10, and the semiconductor substrate 1
1 is stacked on top.

In this embodiment, in addition to the structure of a conventional surface emitting laser device in which a vertical resonator is formed on a semiconductor substrate, a transmission / reflection surface for irregular reflection is provided on the back surface of the substrate on which the output light 14 is extracted. The concave structure 15 provided is provided. The light emitted from the laser oscillator 10 is reflected at the semiconductor-air interface, but by providing the concave structure 15, the direction of the reflected light 13 is changed.
It can be deflected so as not to return to zero. Therefore, the conditions of the AR coat film 12 applied to the back surface can be relaxed. It is also possible to make the concave structure 15 act as an air lens. At this time, by appropriately designing the shape, it is possible to collimate or focus the laser output light, which originally has divergence, according to the purpose.

FIG. 2 is a conceptual sectional view showing a surface emitting laser device according to a second embodiment of the present invention. In the second embodiment of the present invention, the laser oscillator 10 is arranged on the semiconductor substrate 11 at a predetermined interval, and the laser oscillator 10 is provided on the back surface of the semiconductor substrate 11 corresponding to the position of the laser oscillator 10. The tapered structure 16 having a transmission / reflection surface for irregular reflection is provided at intervals corresponding to the price of the laser oscillator 10. Here, the spacing between the laser oscillators 10 may be sufficiently large with respect to the wavelength of the laser light, and it is possible to include a plurality of laser oscillators. In this case, for example, the entire back surface of the semiconductor substrate 11 is included. If it is polished obliquely, the thickness at both ends of the substrate will be greatly different. Therefore, a difference in the output light intensity due to the absorption of the substrate and a difference in the beam diameter due to the beam divergence occur near the location of the substrate. In addition, since the optical length of the substrate can be made uniform with respect to each element by making the laser oscillator and the back surface structure have a one-to-one correspondence as in the second embodiment of the present invention, the problem depending on the above-mentioned location is solved. It can be avoided.

As a method for manufacturing the reflection direction changing structure on the back surface of the substrate as shown in FIGS. 1 and 2, direct drawing etching with a focused charged particle beam and the like can be mentioned. However,
The direct drawing method requires a long time for fabrication, and is not realistic in consideration of adaptation to a two-dimensional integrated device. Therefore,
In the embodiments of the present invention, a photomask which can easily manufacture the structure capable of irregularly reflecting the laser light in the substrate will be described below.

FIG. 3 is a sectional view of a photomask according to the third embodiment of the present invention. In this embodiment, a reflective thin film layer 18 having openings of different diameters is concentrically formed on a glass substrate 17 in order to manufacture a concave structure.
An arbitrary transmitted light intensity distribution can be obtained by sequentially stacking such reflective thin film layers 18. Furthermore, by using, for example, a combination of low reflection chromium (CrO _x ) and high reflection chromium (Cr) as the material of the reflective thin film layer 18, it is possible to obtain a photomask that gives a more ideal transmitted light intensity distribution. Becomes

FIG. 4 shows a first photomask using the photomask of FIG.
It is a conceptual diagram showing the process of manufacturing the concave structure 15 described in the Example. As shown in FIG. 4A, when a photomask is used for pattern transfer in the same manner as in an exposure process using ordinary ultraviolet rays 20, when a positive photoresist 19 is used, the photomask is not exposed under appropriate conditions. The resist shape shown in (b) is formed. By etching this with a method such as reactive plasma etching,
The concave structure 15 as shown in (c) can be formed on the back surface of the substrate.

By using the present photomask in this way, it is possible to easily form a concave structure on the back surface of the substrate as in the case of a normal exposure process. Further, in the present photomask, the necessary structure as described above can be formed by giving a desired transmitted light intensity distribution.

[0021]

As described above, in the surface emitting laser device and the photomask according to the present invention, the nonlinearity (kink) of the laser output-injection current caused by the returning light is obtained by the extremely simple structure and manufacturing method. In addition, noise and mode instability can be reduced. Therefore, the surface emitting laser device of the present invention is also suitable for applications such as high-speed modulation operation that requires a linear response.

[Brief description of drawings]

FIG. 1 is a conceptual cross-sectional view showing a surface emitting laser device according to a first embodiment of the present invention.

FIG. 2 is a conceptual cross-sectional view showing a surface emitting laser device according to a second embodiment of the present invention.

FIG. 3 is a conceptual sectional view showing a photomask which is a third embodiment of the present invention.

4 (a), (b) and (c) are conceptual diagrams showing an example of a surface emitting laser manufacturing process using the photomask of FIG.

FIG. 5 is a conceptual diagram showing a cross-sectional structure of a conventional surface emitting laser.

[Explanation of symbols]

 1 current source 2 p-side electrode 3 p-type semiconductor multilayer film 4,6 clad layer 5 active layer 7 n-type semiconductor multilayer film 8 n-side electrode 9 intermediate layer 10 laser oscillator 11 semiconductor substrate 12 AR coating film 13 reflected light 14 output light 15 Concave Structure 16 Tapered Structure 17 Glass Substrate 18 Reflective Thin Film Layer 19 Photoresist 20 Ultraviolet

Claims (7)

[Claims] 1. A semiconductor substrate having two front and back surfaces,
A surface emitting laser device comprising a semiconductor laminated structure formed on one surface of the semiconductor substrate and extracting laser light from the other surface of the semiconductor substrate facing the one surface, wherein the other surface transmits the semiconductor substrate. A surface emitting laser device having a structure for diffusely reflecting the laser light. 2. The surface emitting laser device according to claim 1, wherein the structure has a transmissive / reflecting surface which is not parallel to one surface on which the semiconductor laminated structure is laminated. . 3. The surface emitting laser device according to claim 2, wherein the transmissive / reflecting surface is a concave surface formed on the semiconductor substrate. 4. The surface emitting laser device according to claim 2, wherein the transmissive / reflecting surface is an inclined surface that intersects a plane parallel to one surface on which the semiconductor layer structures are stacked. Surface emitting laser device. 5. A photomask for forming a structure on one surface of a semiconductor substrate by etching, wherein the photomask is a glass substrate and a transmitted light adjustment layer laminated on the one surface of the glass substrate for adjusting transmitted light. With a multi-layer thin film layer,
The photomask, wherein the multilayer thin film layer has a number of layers corresponding to the pattern of the structure. 6. The photomask according to claim 5, wherein
The photomask, wherein the thin film is a reflective film that reflects light of a predetermined wavelength. 7. A semiconductor substrate having a front surface and a back surface, which has two surfaces, and a semiconductor laminated structure forming a surface emitting laser oscillator provided on one surface of the semiconductor substrate. The semiconductor substrate is transmitted to the other surface opposite to the one surface. A method of forming a structure that diffusely reflects the laser light, wherein the structure is formed by etching the other surface.