JPS5824953B2 - semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser with crystal surface protection.

GaAs-AlxGa1- that can easily perform continuous oscillation at room temperature
The xAs double heterojunction laser has almost solved the problem of rapid deterioration due to crystal defects, and has entered the stage of considering practical application.

However, when the operation continues for more than 1000 hours, the active layer exposed on the reflective surface gradually erodes and changes in quality, causing the surface (
It has become clear that deterioration (Fapley-Perot reflective surface) occurs.

Furthermore, if the device is operated in a high humidity or oxidizing atmosphere, the active layer on the reflective surface will be severely damaged.

However, in various application fields, stable operation under such adverse conditions is required.

Therefore, it is necessary to provide four types of surface protection means, such as providing a thin surface protection film on the active layer portion on the reflective surface of the laser crystal.

However, until now, effective surface protection means against surface deterioration of laser crystals have not been clarified.

On the other hand, many attempts have been made in the past to change the reflectance by attaching a dielectric thin film to the reflective surface and controlling the film thickness, regardless of the surface deterioration countermeasures discussed here.

Materials intended for this reflectance control include SiO, SiO
A wide variety of materials were used.

For this purpose, they even tried to achieve complete reflection by depositing metal on the dielectric thin film.

Furthermore, in addition to the gradual surface deterioration described above, the deterioration of semiconductor lasers is caused by instantaneous damage, usually called optical damage or specular damage, which is destroyed by the light intensity from the reflection surface force axis when a large optical output is produced. known to deteriorate.

Even with such instantaneous deterioration, if a dielectric thin film is provided on the reflective surface to lower the reflectance and make it easier for the laser light to exit the laser crystal (or conversely, reduce the light intensity within the crystal), it will be possible to increase the light output. It is known that optical damage does not occur until

These dielectric thin films, which have conventionally been considered and provided without regard to deterioration countermeasures, only need to be attached to the vicinity of the active layer of about 5μ x 100μ on the reflective surface.
It is difficult to selectively apply a thin film only to such a narrow area, and in reality, it is generally applied to the entire reflective surface in many cases). Until now, countermeasures against deterioration have been insufficient.

Semiconductor lasers for continuous oscillation at room temperature have severe operating conditions, so if this is the main target, surface protection technology can be applied to almost all other semiconductor lasers.

Therefore, unless otherwise specified, the following description will be made with room temperature continuous wave semiconductor lasers in mind.

A laser crystal for continuous oscillation at room temperature is fused to a heat absorber such as Cu or Ila type diamond through a layer of In or Sn to prevent strain from entering the laser crystal.

During fusion, In is heated to 200°C, and Sn is heated to nearly 250°C.

In the case of a conventional surface protective film provided for the purpose of controlling reflectance, etc., a thin film is already attached to the laser crystal before it is fused to the heat absorber, so the thin film is removed by heating during fusion. Problems arose in that the film peeled off and the strength of adhesion to the reflective surface decreased.

This is because the adhesive strength is originally not very high and the coefficients of thermal expansion of the loser crystal and the thin film are different and stress is applied to the thin film.

Also, during handling during the bonding process to the heat sink, the membrane is susceptible to being scratched by tweezers and to many other contaminants.

Furthermore, attaching a thin film only to a small part of the laser crystal, a narrow reflective surface of about 100 μm×100 μm, poses handling risks and is an extremely difficult technique.

Moreover, its industrial productivity is very low. Therefore, providing a thin film on the reflective surface of the laser crystal before adhering it to the heat absorber poses many practical problems.

This problem is a common problem when any surface protective film is provided.

Furthermore, under adverse conditions such as high humidity and oxidizing atmosphere, the adhesive metal such as In or Sn on the heat absorber oxidizes, gradually reducing the strength of the connection between the laser crystal and the heat absorber, and operating for a long time.

This poses a serious practical problem of not being able to withstand storage.

The purpose of the present invention is to provide a semiconductor laser element that avoids peeling of the surface protective film and decrease in adhesion strength caused by the thermal cycle process during adhesion to a heat absorber, and also protects the bonded metal on the heat absorber from the outside air. It is about providing.

According to the present invention, it is possible to obtain a semiconductor laser device in which the same electrically insulating surface protection film is provided on the exposed surface including the reflective surface of the laser crystal bonded to the heat absorber and the exposed bonded metal surface on the heat absorber. .

The principle of the present invention is that the surface protective film on the reflective surface of the semiconductor laser crystal is an electrical insulator.

Electric current flows through the active layer exposed on the reflective surface of the laser crystal, and there is an electric field there, but when outside air comes into contact with it, a chemical reaction occurs and the active layer changes in quality, which is thought to be the main cause of surface deterioration. .

In order to prevent this surface deterioration, Si3N4. Al2O3
It has become clear that thin films such as

In particular, when the active layer contains a small amount of Al, such as in a GaAs AGGat-xAs double heterojunction laser, the active layer and its vicinity are all AlxGa1.
Since it becomes a -xAs mixed crystal, it is chemically active and has excellent adhesion resistance with these thin films, and it has been revealed that the surface protective film according to the present invention is very effective.

These surface protective films are electrical insulators, so if you glue the laser crystal onto the heat absorber and then apply the protective film to the entire surface,
The reflective surface of the laser crystal and the adhesive metal on the heat absorber can be protected from the outside air at the same time.

In this case, since the surface protective film does not go through the thermal cycle process during laser crystal adhesion to the heat absorber, there is no phenomenon of peeling of the surface protective film or decrease in adhesion strength.

Furthermore, according to the present invention, since the exposed adhesive metal surface on the heat absorbing body is also covered and protected with the same protective film that covers the laser crystal surface, deterioration due to oxidation etc. of the adhesive metal on the heat absorbing body does not occur. It is also possible to prevent the phenomenon that the adhesive strength between the laser crystal and the heat absorbing body decreases due to long-term operation or storage.

Furthermore, unlike handling small laser crystals of about 200μ x 300μ x 100μ, we mainly handle relatively large heat absorbers, which solves the difficult problem of handling.

In carrying out the present invention, a laser crystal is usually bonded onto a heat absorber, and then a protective film is formed over its entire surface.

Therefore, in this case, the surface protection film also covers the other electrode that is not bonded to the heat absorber.

However, during ultrasonic bonding when attaching lead wires, if the surface protective film is thin, the protective film will be torn, so the lead wires can be connected and there is no need to remove the protective film on the electrode.

Normally, no problem occurs when the thickness of the surface protective film is determined to meet such conditions.

Note that depending on the material and thickness of the protective film, it may not be possible to remove it during ultrasonic bonding.

In this case, the protective film on the electrode may be removed using a scriber or the like before lead wire bonding.

As a protective film, 5iO9SiO2゜Sia N4,
Electrically insulating dielectric thin films made of A403 or a combination thereof have achieved good results.

If the film thickness is several hundred λ or more, surface deterioration of the reflective surface can be prevented.

If the reflectance of the reflective surface is controlled at the same time, the desired thickness may be used, and the thickness is usually on the order of 1,000 people.

As for the adhesion resistance method of the protective film, already known methods such as sputtering, thermal decomposition, plasma, and coating methods can be used.

These methods have high industrial productivity because hundreds to dozens of samples can be handled at one time.

Note that the semiconductor laser crystal used is the GaAs mentioned above.
-AlxGa1xAs It is not limited to double heterojunction laser crystals, but also single heterojunction or homojunction laser crystals, and of course semiconductor laser crystals made of PbS, PbTe, and many other materials can also be used.

Next, the present invention will be explained with reference to the drawings.

A GaAs-AlxGa1-xAs double heterojunction laser crystal 1 is bonded onto a heat absorber 2 made of Ha type diamond.

The diamond heat absorber 2 is a rectangular parallelepiped whose entire large surface is metallized with Au/Cr, and an adhesive metal Sn layer 3 is deposited to a thickness of 3 μm on the surface to which the laser crystal 1 is to be adhered.

The Au/Cr layer 4, which is the p-type ohmic electrode of the laser crystal 1, and the Sn layer 3 on the heat absorber are heated to 250° C. in a hydrogen atmosphere and fused together.

The n-type ohmic electrode 5 of the laser crystal 1 is made of Au-GeN.
i, on which an A1 layer for ultrasonic lead bonding is deposited to a thickness of 2 μm.

With the laser crystal 1 bonded to the heat absorber 2 in this way,
The SiO2 film 6 is deposited by sputtering to a thickness of approximately 1000 mm.

In this case, SiO□ adheres to all exposed surfaces other than the reflecting surface 7 of the laser crystal.

However, when the Al lead wire 8 is ultrasonically bonded onto the n-type electrode 5, the SiO2 film 6 on the n-type electrode 5 is torn, and the n-type electrode 5 and the Al lead wire 8 are electrically connected. .

The heat absorbing body 2 is mounted on a larger heat radiating body and connected to the (G) electrode of the power source, and the A11I)-domain wire 8 is connected to the (=) electrode of the power source to operate the laser.

In such a laser element, the reflective surface 7 of the laser crystal 1 and the surface of the adhesive metal layer 3 on the surface of the heat absorber 2 are all Si
Since it is protected from the outside air by the 02 protective film 6, it can withstand use even under adverse conditions such as high humidity and oxidizing atmosphere.

After several thousand hours of operation, there was no surface deterioration of the reflective surface I, no deterioration of the adhesive metal layer 3, and no decrease in the adhesive strength between the laser crystal 1 and the heat absorber 2, allowing stable continuous operation at room temperature in normal air. I was able to do it with

Since the surface protective film 6 is electrically insulating, even if the protective film 6 is adhered to the structure shown in the figure, it will not cause any electrical problems to the element.

The sputtering method, which is convenient for forming the protective film 6, requires several hundred sides.
~ Dozens of samples can be processed at once, and the heat absorber, which is much larger than the laser crystal, can be handled as the main material, and the industrial productivity of the present invention is high.Also, the thin film can only be applied to the reflective surface of the laser crystal This also solves the problem of being small and difficult to handle, unlike when it is installed.

Considering the principle of surface deterioration, in the case of either a striped laser or a normal full-wavelength laser, it is much more desirable to have a surface protective film on the sides other than the reflective surface 7 as shown in the figure. It's obvious.

In view of the principle and gist of the present invention, the type of surface protective film and its adhesion resistance method, the type of laser crystal and heat absorber, the type of adhesive metal, the type of lead wire and the method of connecting the lead wire, etc. are as described above. Needless to say, it is not limited to things.

[Brief explanation of the drawing]

The figure is a cross-sectional view for explaining an embodiment of the present invention, and 1 is a GaAa
-AAXGal-xAIl double heterojunction laser crystal, 2 is an lla type diamond heat absorber, 3 is a Sn adhesive metal layer, 6 is an S102 surface protection film, and 7 is a reflective surface of the laser crystal.

Claims (1)

[Claims] 1. A semiconductor laser element characterized in that the exposed surface including the reflective surface of a semiconductor laser crystal bonded on a heat absorber and the exposed bonded metal surface on the heat absorber are coated with the same electrically insulating surface protection thin film. .