JPH0648742B2 - Method for manufacturing semiconductor laser - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor laser manufacturing method capable of obtaining a high-output and efficient semiconductor laser with high mass productivity.

[Conventional technology]

Here, Metal-Organic Vapor
An AlGaAs / GaAs semiconductor laser using the Phase Epitaxy method (hereinafter abbreviated as MOVPE method) will be described as an example.

FIG. 3 shows the structure of a semiconductor laser according to the prior art (for example, Proceedings (IEDM'83 Proceeding) 2
92-295) and FIG. 4 is a sectional view showing the manufacturing process. M on the n-type GaAs substrate 12
N-type Al _0.45 Ga _0.55 As layer 13, Al by the OVE method
_0.15 Ga _0.55 As active layer 14, p-type Al _0.45 Ga _0.55 A
The s layer 15 and the n-type GaAs current blocking layer 16 are sequentially stacked (FIG. 4A), and the n-type GaAs current blocking layer 16 is formed.
A groove 17 penetrating through is formed by selective etching (FIG. 4 (b)). After that, p-type Al is formed by MOVPE method.
_{A 0.45} Ga _0.55 As layer 18 and a p-type GaAs layer 19 are formed (FIG. 4 (c)), and finally a p-electrode 20 and an n-electrode 21 are formed to complete the semiconductor laser of FIG. 3 (FIG. 3). ). Current confinement is performed by the current blocking layer 16, and the transverse mode of the laser light is set as the fundamental mode due to the difference in effective refractive index and high absorptivity between the region of the groove 17 and other regions.

[Problems to be solved by the invention]

In this semiconductor laser, since the laser light is largely absorbed in the region in contact with the groove 17, the transverse mode is stable with a high optical output. Further, the current is confined in the groove 17 by the n-type GaAs current blocking layer 16, and the region where the transverse mode is guided and the region where the current is injected coincide with each other, so that the laser operation is stable.

When this laser is operated with a high optical output, the end face of the laser resonator may be broken by the laser beam,
If the laser is operated for a long time, the deterioration proceeds from the end face of the laser resonator. For this reason, a protective film such as SiO ₂ or Al ₂ O ₃ is usually formed on the end face of the laser resonator. However, since the laser crystal and the protective film are different materials, for example, 5
Under a very high light output of 0 mW, the protection effect is not sufficient, and the end face destruction or deterioration progresses.

An object of the present invention is to solve these problems and provide a method for manufacturing a semiconductor laser in which such end face destruction and deterioration are prevented.

[Means for solving problems]

The structure of the method for manufacturing a semiconductor laser of the present invention is such that, on a semiconductor substrate of the first conductivity type, a first semiconductor layer of the first conductivity type, a layer thickness of 200 Å or less, and a band gap smaller than that of the first semiconductor layer. An active layer and a second semiconductor layer having a layer thickness of 200 Å or less and a bandgap larger than that of the active layer are alternately laminated to form a multilayer film, and the refractive index of the semiconductor layer having an averaged composition is the above-mentioned refractive index. A superlattice layer larger than one semiconductor layer and a third semiconductor layer of the second conductivity type having a smaller refractive index than the semiconductor having an averaged composition of the superlattice layer are sequentially grown to form a semiconductor substrate crystal. The first step,
A second conductivity type impurity is diffused or ion-implanted in a region of the semiconductor substrate crystal, which is to be a cavity end face of a semiconductor laser, to a depth reaching the superlattice layer, and the composition of the superlattice layer is averaged. Step, and leaving the stripe-shaped region parallel to the resonator of the semiconductor laser,
A third step of selectively etching to a depth not penetrating the semiconductor layer, and a high resistance or first conductivity type that selectively absorbs light emitted from the superlattice layer in a region other than the stripe-shaped region And a fourth step of forming the semiconductor layer.

[Action]

The composition of the superlattice layer serving as the active region according to the present invention is a portion that becomes the resonator of the laser, and the composition is averaged by the process of impurity diffusion or ion implantation. Since the layer is transparent to the light emitted from the superlattice layer, the protective film made of the same material as the laser crystal is formed on the end facet of the laser resonator. Furthermore, even at the laser cavity end face, light is guided by the step of the refractive index in the vertical direction of the superlattice layer whose composition is averaged, and in the horizontal direction by loss guiding by the buried layer. The coupling efficiency of light is high, and the laser operation with the same efficiency as a normal laser having no structure on the end face is possible.

〔Example〕

FIG. 1 is a sectional view showing the structure of a semiconductor laser obtained by a method for manufacturing a semiconductor laser according to an embodiment of the present invention, and FIGS. 2 (a) to 2 (d) are elements showing the manufacturing method in FIG. 1 in the order of steps. FIG. First, the first MOVPE growth is performed to form n-type Al _0.45 Ga _0.55 As on the n-type GaAs substrate 1.
Layer 2, AlAs layer with 40 Å thickness and GaAs with 80 Å thickness
Superlattice layer with alternating layers 3, p-type Al _0.45 Ga _0.55
An As layer 4 and a p-type GaAs layer 5 are sequentially formed (FIG. 2 (a)). Next, a Zn diffusion layer 6 having a depth reaching the superlattice layer is formed in a portion which will be the end facet of the laser cavity, and the composition of the superlattice layer 3 is averaged (FIG. 2 (b)). After this, Si
Selective etching is performed to a depth that does not reach the superlattice layer 3 using the O ₂ film 10 as a mask to form a stripe-shaped mesa 11 parallel to the laser cavity direction (FIG. 2 (c)).
Further, a second MOVPE growth is performed to form n-type GaAs 7 (FIG. 2 (d)). Finally, the p-electrode 8 and the n-electrode 9 are formed to complete the semiconductor laser (FIG. 1).

〔The invention's effect〕

As described above, in the semiconductor laser of the present invention, it is utilized that the layer obtained by Zn diffusion and averaging the composition of the superlattice layer 3 is transparent to the light emitted from the superlattice layer 3. , Generate a window region for the laser light on the laser end face. Therefore, the laser end face is not destroyed by the laser light even in the operation of high light output, and this window region functions as a protective film for preventing crystal deterioration from the laser end face. In this case, since the same crystal as the laser crystal is used as the protective film, no stress is generated, and Si in the conventional example is not used.
It is superior to O ₂ and Al ₂ O ₃ protective films.

Further, even in the window region, the superlattice layer having an averaged composition has a larger refractive index than the semiconductor layer in contact with it, and the n-type GaAs layer 6 absorbs the laser beam, so that the laser facet and the inside of the laser also have the same structure. Perpendicular to the superlattice layer 3,
The light is guided in the horizontal direction, and the coupling efficiency of the laser light inside the laser and in the window region can be made equal to that in the case without the window region.

In addition, n-type Al _0.45 Ga _0.55 As layer 2, p-type Al _0.45 G
Since the a _0.55 As layer 4 and the n-type GaAs 7 form an NPN thyristor, they serve as a current blocking layer.

Therefore, in the semiconductor laser manufactured according to the present invention, both the carrier and the light are effectively confined in the active region, the oscillation threshold is low, and the laser end face is not destroyed up to a high optical output, and a stable basic Transverse mode oscillation can be performed. Also, the reliability in high light output operation is good.

In the description of the present invention, A using the MOVPE method is used.
Although the description has been made by taking the 1GaAs / GaAs semiconductor laser as an example, it is obvious that the present invention can be applied to semiconductor lasers of other materials based on the vapor phase growth method or the molecular beam epitaxial method other than the MOVPE method.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of the structure of a semiconductor laser obtained by the manufacturing method of the present invention, FIG. 2 is a process diagram showing an example of the manufacturing method thereof, and FIG. 3 is an example of the structure of a semiconductor laser according to the prior art. And FIG. 4 is a process drawing showing the manufacturing method. 1,12 ... n-type GaAs substrate, 2,13 ... n-type Al
Al _0.45 Ga _0.55 As layer, 3 ... Superlattice layer, 4, 15,
18 ... p-type Al _0.45 Ga _0.55 As layer, 5, 19 ... p
-Type GaAs layer, 6 ... Impurity diffusion layer, 7, 16 ... N-type GaAs layer, 8, 20 ... P-electrode, 9, 21 ... N-electrode, 10 ... SiO ₂ film, 11 ... Mesa, 14 ...... Al
_0.15 Ga _0.55 As active layer, 17 ... Groove.

Claims (1)

[Claims] 1. A first conductivity type first semiconductor layer, an active layer having a layer thickness of 200 Å or less and a band gap smaller than that of the first semiconductor layer, and a layer thickness 20 on a first conductivity type semiconductor substrate.
A second semiconductor layer having a thickness of 0 Å or less and a bandgap larger than that of the active layer is alternately laminated to form a multilayer film, and the refractive index of the semiconductor layer having a composition obtained by averaging the multilayer film is the first layer.
A superlattice layer larger than the semiconductor layer and a third semiconductor layer of the second conductivity type having a smaller refractive index than the semiconductor having a composition obtained by averaging the superlattice layer are sequentially crystal-grown to form a semiconductor substrate crystal. The first step, and the composition of the superlattice layer is averaged by diffusing or ion-implanting the second conductivity type impurity to a region of the semiconductor substrate crystal, which is to be a cavity end face of the semiconductor laser, to a depth reaching the superlattice layer. The second step of
A third step of selectively etching to a depth not penetrating the third semiconductor layer leaving a striped region parallel to the cavity of the semiconductor laser, and selecting a region other than the striped region And a fourth step of forming a high resistance or first conductivity type semiconductor layer that absorbs light emitted from the superlattice layer.