JPH071817B2 - Semiconductor laser - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser which prevents end face deterioration of a visible light semiconductor laser and obtains high output and stable operation for a long time.

Conventional technology Semiconductor lasers, especially AlGaAs and AlGaInP visible light semiconductor lasers, are used as light sources for optical information processing in printers, optical discs, digital audio discs, etc. High output is desired.

In order to achieve long life and high output of semiconductor lasers, it is important to prevent the deterioration of the cavity facets. There are two types of end surface deterioration, one is deterioration caused by chemical alteration due to absorption and adsorption of moisture and oxygen in the atmosphere, and the other is caused by local concentration of optical power density during high output operation. It is optical damage (Catastrophic optical damage, COD).

Conventionally, for the end surface deterioration, the semiconductor laser is sealed in a dry nitrogen gas atmosphere, or the end surface is coated with Al ₂ O ₃ or SiO ₂ . On the other hand, the latter optical damage may be achieved by making the end face transparent to the laser light and eliminating the absorption at the end face, and a wind-striped semiconductor laser and the like have been devised based on this.

The problem to be solved by the invention However, it cannot be said that even if an amorphous film such as Al ₂ O ₃ or SiO ₂ is used as the conventional end face protective film, the above-mentioned drawbacks are essentially prevented. In other words, the adhesion of the protective film is insufficient and a large number of pinholes are generated, so that adsorption and absorption of moisture, oxygen and the like are large, and there is a drawback that the end face protection does not function sufficiently. In particular, considering the shortening of the wavelength, both AlGaAs and AlGaInP contain a large amount of active Al,
Oxidation of the end face became faster, which was a serious problem.

From the viewpoint of adhesion, it can be solved by growing a single crystal transparent to laser light on the end face. However, AlGaAs and AlGaInP, which are III-V group compound semiconductors, having a high Al composition ratio are easily oxidized. II-VI semiconductor materials, such as ZnSe, ZnTe, and ZnS, have the drawback that a good single crystal is difficult to form on a damaged surface such as an etching end face, and pinholes are generated.

Therefore, an object of the present invention is to provide a visible light semiconductor laser capable of eliminating the above-mentioned defects of the end face protective film at the same time and capable of stable operation at high output and for a long time.

Means for Solving the Problems Technical means of the present invention for solving the above problems are two or more kinds of II-VI groups which are transparent to laser light as an end face protective film on an end face of a cavity of a visible light semiconductor laser. This is to epitaxially grow a strained superlattice layer made of a semiconductor. These strained superlattice layers are formed by, for example, vapor phase epitaxy or molecular beam epitaxy.

Action The action of the present invention is as follows. When a II-VI group semiconductor strained superlattice layer is epitaxially grown on the end face of a visible light semiconductor laser cavity of AlGaAs, AlGaInP system, the interface between the two is Al.
Adhesion is better than that of ₂ O ₃ and SiO ₂ , and the surface of the strained superlattice is extremely good with no pinholes or irregularities. In particular, even if the end face of the cavity is an etching end face including damage, there is almost no problem. As a result, deterioration on the end surface is significantly suppressed.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

Example 1 As shown in FIG. 1, on an n ⁺ -GaAs substrate 1, an n-Al _0.5 Ga _0.5 As layer 2 as a first cladding layer and an undoped layer as an active layer.
Al _0.1 Ga _0.9 As layer 3, p-Al _0.5 Ga _0.5 As as second cladding layer
A layer 4 and a p-GaAs layer 5 as a cap layer were sequentially epitaxially grown by the MOVPE method. The SiO ₂ film 6 is provided on this surface,
After forming the slit-shaped stripe window, AuGe / Au and Ti / Pt / An were deposited as the n-side electrode 7 and the p-side electrode 8, respectively. After that, the resonator end face 9 was formed by cleavage. ZnSe (30Å) and ZnS (30Å) as the end face protective film 10
Was grown epitaxially by MOVPE method. At this time, the epitaxial growth was performed at a low temperature of 250 ° C. using dimethylzinc (DMZ), hydrogen selenide (H ₂ Se) and hydrogen sulfide (H ₂ S) as source gases. next,
It was cut into a predetermined size, mounted and packaged to obtain a semiconductor laser.

Second Embodiment Next, a case where the semiconductor laser and the photodetector shown in FIG. 2 are monolithically integrated will be described.

In this case, the cavity facet of the semiconductor laser cannot use the cleaved facet as shown in the first embodiment, and therefore must be formed by chemical etching or reactive ion etching.

The manufacturing method will be briefly described. A SiO ₂ film is formed on the same AlGaAs-based laminated structure formed by the MOVPE method as in Example 1, an opening is formed, and resonance is performed using the SiO ₂ film as a mask by reactive ion etching using CCl ₄ as a reactive gas. The device end surface 9b and the separation groove 11 were formed. Then immediately
According to the MOVPE method, ZnSe (30Å) and ZnS (30
The 10-period strained superlattice layer of Å) was epitaxially grown to form the end face protective film 10. Then, remove the SiO ₂ film and
An O ₂ film 6 was provided, slit-shaped stripe windows were formed on the semiconductor laser and the photodetector, and n-side and p-side electrodes were provided. Since the surface of the strained superlattice on the end face was good with no pinholes or irregularities, there was no damage, corrosion, or oxidation of the resonator end face due to the process after forming the end face protective film. It is also possible to form the resonator end face 9b after forming the electrodes, and in this case,
The end face protective film 10 is formed at the final stage of the manufacturing process, but it is not necessary to apply high heat as in the first embodiment.

For comparison, only ZnSe was epitaxially grown,
A large number of pinholes were generated and a good surface could not be obtained.
It is considered that this is because the etching end surface 9b was not flat as compared with the cleavage 9a, and defects were introduced by reactive ion etching on the surface. However, when the strained superlattice is used, pinholes and the like are unlikely to occur even if there are a few oxide films or defects on the end surface.

In the above description, ZnSe and ZnS were used as the strained superlattice layer, but ZnSe and ZnSSe mixed crystal, ZnSe and ZnTe, ZnSe and ZnSeTe.
It may be a mixed crystal or a combination of these mixed crystal semiconductors, and the film thickness and layer period of each layer may be appropriately selected.

Further, as the visible light semiconductor laser, the AlGaAs type is shown in the embodiment, but the AlGaInP type is also applicable. Further, although the MOVPE method is used as the growth method of the strained superlattice layer, the molecular beam growth method or another vapor phase growth method can be applied.

EFFECTS OF THE INVENTION As described above, according to the present invention, a strain composed of two or more kinds of II-VI semiconductors transparent to laser light is used as an end face protective film of a visible light semiconductor laser lattice-matched with GaAs. The use of the superlattice layer improved the adhesion of the end face protective film and eliminated the occurrence of pinholes. As a result, oxidation of the end face due to adsorption and absorption of water and oxygen was prevented, and it became possible to extend the life and increase the output of the visible light semiconductor laser. In particular, the effect is great when forming on the etching end face.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing a semiconductor laser according to an embodiment of the present invention, and FIG. 2 is a sectional view showing a structure of a monolithic integrated device including a semiconductor laser and a photodetector according to the second embodiment. is there. 1 …… n ⁺ -GaAs substrate, 2 …… n-Al _0.5 Ga _0.5 As layer, 3 ……
Undoped GaAs layer, 4 …… p-Al _0.5 Ga _0.5 As layer, 5 …… p-
GaAs layer, 6 ... SiO ₂ film, 7 ... N-side electrode, 8 ... P-side electrode, 9a, b ... Resonator end face, 10 ... End face protective film, 11 ... Separation groove.

Claims (4)

[Claims] 1. A semiconductor laser in which a strained superlattice layer composed of two or more kinds of II-VI semiconductors is epitaxially grown on an end face of a cavity. 2. The laser body is AlGaAs lattice-matched to GaAs.
The semiconductor laser according to claim 1, wherein the semiconductor laser is made of AlGaInP-based material. 3. The semiconductor laser according to claim 1, wherein the strained superlattice layer is epitaxially grown by a vapor phase growth method or a molecular beam growth method. 4. The semiconductor laser according to claim 1, wherein the cavity end face is formed by etching.