JPS5853520B2 - semiconductor laser equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to extending the life of a semiconductor laser, and particularly to a heterojunction semiconductor laser device used near room temperature.

Conventionally, when semiconductor lasers are operated at room temperature, their lifetimes are short, and it has been known that they sometimes degrade within minutes or even seconds.

Although the cause is still unclear, it has been confirmed that a region of high absorption occurs near the output surface of the laser beam.

This absorption is presumed to be due to defects created in the crystal near the surface due to a combination of factors such as molecules adsorbed on the surface of the semiconductor crystal, laser light, electric field, and heat.

Absorption due to this defect is wavelength dependent, with strong absorption particularly for light near the band width energy, and almost no absorption for light with energy smaller than the band width.

In order to prevent the above-mentioned deterioration, it is sufficient to prevent the adsorbed molecules from coming into contact with the semiconductor performing the laser operation.

An object of the present invention is to provide a long-life, practical semiconductor laser device in which the above-mentioned defects are eliminated.

Conventionally, for this purpose, there has been a method of depositing a thin film of Sin, 5i02, etc. on the light emitting output surface using a method such as vapor deposition, but in this case, these films often belong to a crystal system different from that of the semiconductor. , therefore the adhesion is poor.

Furthermore, it is difficult to satisfy the requirements of a protective film and an optical interference film at the same time.

That is, it is desirable that the protective film has a certain degree of thickness, and it also needs to be chemically dense, so it generally needs to be manufactured at a high temperature.

As for optical properties, it is necessary to precisely control the thickness of about 1/4 or 1/2 wavelength due to its properties as an interference film.

Satisfactory results can be obtained by satisfying these requirements separately.

In other words, by partially changing the composition of the semiconductor crystal as a protective film on the light emitting output surface of the semiconductor crystal that performs laser operation and its neighboring region so that the band width is larger than the emitted energy, a long-life semiconductor laser can be realized. Obtainable.

In this case, a feature of the present invention is that the protective layer is a semiconductor crystal region having a bandwidth larger than the bandwidth of the semiconductor operating as a laser or the energy of the laser beam.

In other words, by forming such a semiconductor region, the probability of defects occurring in the semiconductor protective layer decreases,
Moreover, even if a defect occurs, absorption due to the defect occurs near the band width of the protective layer semiconductor, but since it does not absorb laser light, it does not affect laser operation.

Next, examples of the present invention will be described.

A generally well-known liquid phase epitaxial growth method (for details, see, for example, the article by Hayashi et al. in Applied Physics Letters, Vol. 17, pp. 109-111).

) The composition of the semiconductor crystal was changed as shown in Figure 1 by using ion implantation method into the cleaved end facet of a so-called GaAs double heterojunction laser made from GaAs or a method of diffusing phosphorus (P) into GaAs. By partially changing the energy density, the diffused portion 8 is formed as a protective layer with a large energy gap.

By selecting the conditions for forming this protective layer, it is possible to
When a semiconductor laser with a stripe width of m was operated at room temperature DC at 30 mW, no deterioration was observed for more than 5000 hours.

When a life test was conducted under the above conditions without forming this protective layer, the laser showed significant deterioration after several tens of hours.

This situation is shown in FIG.

The curve a in FIG. 2 is an example of the laser of the present invention in which a semiconductor layer with a large energy gap is formed, and the curve a is an example of a conventional laser in which a protective layer is not formed.

In terms of optical output, the laser of the present invention has also been significantly improved compared to conventional lasers.

This situation is shown in FIG. In FIG. 3, the horizontal axis represents the current flowing through the laser, and the vertical axis represents the optical output from the laser.

In the figure, the curve shown with a solid line shows the laser characteristics of the present invention, and the curve shown with a dotted line shows the characteristics of the conventional laser.

Although not specifically mentioned in the embodiments, it goes without saying that an optical interference film may be attached to the scales if necessary.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing the aging characteristics of the laser of the present invention and a conventional laser, and Fig. 3 is a diagram showing an example of the present invention.
The figure is a diagram showing the optical output characteristics of the laser of the present invention and a conventional laser. In the figure, 1, 6...electrode, 2...p type A
I 035 , Ga0.65As layer, 3...
・GaAs active layer, 4...n-type At□, 3i
s GAO, 65As layer, 5--GaAs substrate, 8...
...Indicates a layer in which impurities are diffused and the band width is increased.

Claims (1)

[Claims] 1. A semiconductor laser device characterized in that a protective layer having a bandwidth larger than the emission energy is formed by changing the composition of a region near the emission output surface of a semiconductor crystal forming the semiconductor laser element.