JPH11307865A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve heat radiation by laminating a metal film and dielectric film on at least a part of the end face of a semiconductor laser device. SOLUTION: An InGaAsP laminate layer having a p-n junction (light emission layer) with specified compsn. and impurity concn. is epitaxially grown in a GaAs substrate 7, the GaAs substrate 7 is polished to reduce the thickness, electrodes 4, 4' are formed, the front and rear end faces 10, 10' are exposed by cleaving, a dielectric reflective film 2' is deposited by the sputtering method on the exposed semiconductor laser rear end face 10', an Al metal film 6 is deposited on the semiconductor laser entire end face 10, the Al film covering the light emitting part is removed to form an opening 5, and the same dielectric reflective film 2 is deposited. The end face is formed by cleaving, hence the bonding property of the metal film and top face flatness can be improved and heat radiation can be improved as well as the suppression of the peeling of the dielectric film and metal film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a semiconductor laser, and more particularly to providing a highly reliable end face structure having excellent heat radiation characteristics.

[0002]

In a conventional semiconductor laser, reflective film 2 having a predetermined reflectivity of the layer film of dielectric such as SiO _2, SiN film on the end face of the semiconductor crystal 1 as shown in FIG. 1,
2 'is formed, thereby reflecting and transmitting the light generated inside the semiconductor crystal 1 at a predetermined ratio, taking out the light output 3, 3' to the outside, and protecting the semiconductor end face, thereby providing reliability. Was ensured. Such a conventional technique is described in, for example, pages 8 to 9 or 2 of "Semiconductor Laser" Baifukan (1984), edited by Ryoichi Ito and Michiharu Nakamura.
It is explained from page 45 to page 246.

[0003]

However, the above-mentioned dielectric film generally has poor thermal conductivity, and the amount of heat generated at the end face increases as the output of the semiconductor laser increases. In particular, the main light output 3 emitted from the front end face (the right end in FIG. 1) of the semiconductor laser generates a large amount of heat, so that the heat generated in the dielectric film cannot be quickly removed, and the end face is rapidly deteriorated. .

[0004]

The structure of a semiconductor laser device suitable for solving the above problem will be described with reference to FIG. In a semiconductor laser end face, particularly in a semiconductor laser in which the end face is formed by a cleavage method, a portion of the end face where the laser light 3 is emitted is very small. The inventor has found that the above problem can be solved, for example, by coating the end face with a film 6 having a good thermal conductivity and a stable external environment, such as a metal provided with an opening 5 as shown in FIG. . At this time, the opening 5 corresponding to the light emitting portion uses the same dielectric film 2 as the conventional one because the optical characteristics are important. However, unlike the conventional one, the metal film 6 is located immediately around the light emitting portion. It is removed by the metal film.

That is, the semiconductor laser device of the present invention is characterized in that a metal film 6 and a dielectric film 2 are laminated in this order on at least a part of an end face thereof. From the viewpoint of suppressing the influence of the diffusion of the metal element from the junction surface of the metal film 6 with the end face to the laser resonator, it is preferable that the constituent element of the metal film be selected from Group III elements such as Al. It is also desirable that ion implantation or the like be performed along the end face of the laser resonator so that the electrical resistance is higher than that inside the resonator.
These are effective in suppressing the current injected for laser oscillation from bypassing the metal film. The above effect can be expected even if a Schottky junction is made between the metal film and the end face. From this viewpoint, the use of the group III element (element which does not act as a dopant even when diffused into the semiconductor layer) is recommended.

The metal film may have an opening formed in the laser light emitting portion on the end face, and the dielectric may be attached to this portion. However, this does not apply when the thickness of the metal film is small enough not to hinder practical laser light emission. Further, the dielectric may be formed in a lens shape on the laser beam emitting portion to enhance optical coupling with another optical element. Furthermore, when the end face is formed by cleavage, the bonding property of the metal film and the flatness of the upper surface thereof can be improved, so that peeling of the dielectric film and the metal film can be suppressed, as well as heat dissipation. When mounting the semiconductor laser device of the present invention on a heat sink, the metal film extends to an upper portion or a lower portion of the device end surface so as to be in contact with the heat sink, and is either a p-type or an n-type bonded to the heat sink. When connected to the electrodes, the heat dissipation is improved.

[0007]

FIG. 2 shows a first embodiment of the present invention.
The semiconductor laser shown in FIG. In the semiconductor laser according to the present invention as shown in FIG. 2, the front end face of the semiconductor laser is covered with a metal film 6 having an opening 5 at a light emitting portion, and a dielectric reflection film 2 is applied on the metal film. You.

FIG. 3 is a view of the semiconductor laser of FIG. 2 as viewed from the front end face direction. The metal film 6 is provided with an elliptical opening 5 at a light emitting portion, and the opening 5 is covered with only the dielectric reflection film 2 as in the conventional case, and the light reflection and transmission characteristics are the same as those in the conventional case. There is no change.

Such an end face structure is produced, for example, by the manufacturing steps shown in FIGS. Although the end face structure according to the present invention can be applied to all semiconductor lasers that form an end face by cleavage, in this embodiment, GaAs / In
A GaAsP-based semiconductor laser will be described.

An InGaAsP laminated film 8 having a pn junction (light emitting portion) formed with a predetermined composition and impurity concentration on a GaAs substrate 7 is epitaxially grown (FIG. 4A). A light-emitting portion is formed to a predetermined size by photolithography and wet etching (FIG. 4B), and p-type InGaP9 is epitaxially regrown around the light-emitting portion so that current does not leak to a portion other than the light-emitting portion (FIG. 4C). The figures up to this point are views seen from the light emission direction.

Next, the thickness of the GaAs substrate is reduced by polishing, electrodes 4 and 4 'are formed, and the front end face 10 and the rear end face 10' are exposed by cleavage (FIG. 5a). Here, the drawing direction is different from those of FIGS. 4a to 4c by 90 degrees in FIG. 4 and is a view from the side of the semiconductor laser. The process up to this point is the same as the conventional semiconductor laser manufacturing process.

A conventional dielectric reflection film 2 'is applied to the exposed rear end face 10' of the semiconductor laser by sputtering, and a metal Al film 6 is applied to the front end face 10 of the semiconductor laser.
Is sputtered to a thickness of 200 nm (FIG. 5b).

Next, an Al film covering the light emitting portion is removed by a processing machine using a focused ion beam to form an opening 5, and a dielectric reflection film 2 same as that of the related art is applied, and FIG. 5C (same as FIG. 2) Is completed. At this time, the ion beam was stopped just before Al was completely removed and the semiconductor was exposed so as not to damage the semiconductor surface by the ion beam, and the remaining slight Al was removed by undamaged wet etching. The reason why the ion beam processing machine was used for processing the Al film is that normal photolithography technology cannot be used because the workpiece is very small.

FIG. 6 shows the correlation between the input current and the optical output of a semiconductor laser having such a structure and a conventional semiconductor laser. The semiconductor laser according to the present invention has excellent heat dissipation at the end face, so that output saturation due to heat generation is suppressed, and the maximum output is improved by about 30%.

FIG. 7 is a diagram showing a second embodiment of the present invention. 7, the stacking order of the metal film 6 and the dielectric film 2 on the end face is reversed, unlike FIG. In this structure, the semiconductor surface is protected during the processing of the metal film using the ion beam, so that there is an advantage that it is not necessary to stop the ion beam immediately before the processing of the metal film is completed.

FIG. 8 shows a third embodiment, in which a laminated structure similar to the front surface of a semiconductor laser is also provided on the rear end surface of the semiconductor laser. Normally, the rear end face outputs only a fraction of the light output 3 'of the front light output 3 for the light receiving element for monitoring, so that the thermal load is weaker than the front face. However, with a high-power laser, heat generation cannot be ignored even at the rear end face. The method of covering both end faces with a metal film as in this embodiment is extremely effective particularly for a high-output semiconductor laser.

FIG. 9 is a diagram showing a fourth embodiment. In this embodiment, an opening was formed in the metal film in the same process as in the first embodiment, and then a SiO ₂ film was applied by a sputtering method. In this method, since the film formation speed is low around the opening, the film thickness is different between the center and the periphery of the opening, thereby forming the dielectric film 2 having a convex lens shape. For this reason, a micro lens conventionally used for converging light to an optical fiber or the like becomes unnecessary, and the assembling process is greatly simplified.

FIG. 10 shows a fifth embodiment, in which a low-melting glass 11 is used as a dielectric film. When the low-melting glass film 11 is formed on the metal film 6 provided with the opening, and once melted and solidified again by heating, a concave lens-like film having a large film thickness around the opening is formed. In such a structure, light is diffused, so that the light can be made safe for eyes and the like.

[0019]

As described above, according to the present invention, not only can a large-output, high-reliability semiconductor laser excellent in heat dissipation be constructed, but also a semiconductor laser that does not require an external microlens can be realized. The industrial benefits are great.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a conventional semiconductor laser.

FIG. 2 is a sectional view of a first embodiment of the semiconductor laser of the present invention.

FIG. 3 is a front view of the semiconductor laser of FIG. 2 viewed from an end face direction.

FIG. 4 is a sectional view showing a manufacturing process of the semiconductor laser of FIG. 2;

FIG. 5 is a sectional view showing a manufacturing process of the semiconductor laser of FIG. 2;

FIG. 6 is a diagram showing light output characteristics of the semiconductor laser of the present invention and a conventional example.

FIG. 7 is a sectional view of a second embodiment of the semiconductor laser of the present invention.

FIG. 8 is a sectional view of a third embodiment of the semiconductor laser of the present invention.

FIG. 9 is a sectional view of a fourth embodiment of the semiconductor laser according to the present invention.

FIG. 10 is a sectional view of a fifth embodiment of the semiconductor laser of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor crystal, 2,2 '... Dielectric film, 3,3' ... Light output, 4,4 '... Electrode, 5 ... Opening, 6 ... Metal film, 7 ... G
aAs substrate, 8 ... InGaAsP laminated epitaxial crystal, 9
... InGaAs regrown epitaxial crystal, 10, 10 '... cleavage end face.

Claims (4)

[Claims] 1. A semiconductor laser, wherein at least a part of an end face of the semiconductor laser is covered with a laminated film of a metal and a dielectric. 2. The semiconductor laser according to claim 1, wherein, at the end face of the semiconductor laser, a light emitting portion is covered with a dielectric, and the other portion is covered with a laminated film of a metal and a dielectric. 3. The semiconductor laser according to claim 2, wherein the dielectric covering said light emitting portion is in the form of an optical lens. 4. The semiconductor laser according to claim 1, wherein an end face is formed by cleavage.