JP3015371B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a semiconductor laser used as a light source for optical information processing, optical measurement, and the like.

(Prior Art) In recent years, semiconductor lasers have been widely used in the fields of optical information processing, optical communication, and optical measurement. These semiconductor lasers are required to have characteristics according to their uses. For example, a semiconductor laser used in an optical disk system for a video disk, a document file, or the like is required to be in a basic transverse mode within a range of an optical output to be used and to have small astigmatism. As a semiconductor laser satisfying such a specification, for example, a GaAlAs laser (Ext
ended Abstruct, 17th Conf.on Solid State Devices an
d Materials, Tokyo (1985) pp. 67-70) and the ridge stripe type InGaAlP laser (Extended Abstru
ct, 17th Cenf.on Solid State Devices and Materials,
There is a transverse mode control semiconductor laser such as Tokyo (1986) pp.153-156).

In the example of FIG. 3, since the optical waveguide layer 105 is provided near the active layer 102 at the stripe portion, a difference in effective refractive index occurs between the inside and outside of the stripe, and stable fundamental transverse mode oscillation occurs. Is achieved. The current confinement layer 104
Since GaAlAs having a larger forbidden band width than the active layer 102 can be used, characteristics of low loss and low astigmatism can be obtained. However, this structure does not
After forming 110 by etching, optical waveguide layer 105,
In order to grow the cladding layer 106 and the contact layer 107, a regrowth step on the Al-containing crystal at the stripe portion where the current flows is included.From the viewpoint of the crystal quality of the interface, the Al composition ratio of the cladding layer is reduced. If it is large, or it is difficult to apply to other material systems, for example, InGaAlP system.

FIG. 4 solves this problem. Since the GaAs cap layer 125 remains when the ridge portion is etched, regrowth on a crystal containing Al is not included in a portion where current flows. In this structure, the GaAs current confinement layer 124 outside the stripe is the active layer 1
Since it is close to 22, the loss of the waveguide mode is larger than that of the ridge, an effective refractive index is generated inside and outside the ridge, and the transverse mode is confined. Since this structure is a loss guided type, the stability of the transverse mode can be obtained even if the stripe width W is made larger than in the case of FIG. 3, but the loss is large and the astigmatism is small as compared with FIG. growing. In addition, when InAlP is used as the cladding layer as in the example of this figure, the difference in the forbidden band width with the active layer is large, and a low threshold characteristic is obtained. As the optical power density increases, there is a limit to high output.

In both cases of FIGS. 3 and 4, the transverse mode characteristics greatly depend on the stripe width W and the dimension h in each drawing. Although W can be sufficiently controlled by the dimensional accuracy of the photomask, h is a size determined by the etching conditions, and therefore, a high-level technique is required to perform precise dimensional control.

(Problems to be Solved by the Invention) As described above, in the conventional semiconductor laser, there is no regrowth interface containing Al in a region where current flows, and low loss,
A transverse mode control structure having characteristics such as low astigmatism and high output has not been realized. Further, there is a problem that it is difficult to control the structure dimensions to obtain stable transverse mode characteristics. SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and to provide a semiconductor laser capable of easily performing dimensional control for obtaining a stable fundamental transverse mode and capable of high-power operation.

[Configuration of the invention]

(Means for Solving the Problems) According to the present invention, the forbidden band width of the current constriction layer is larger than the forbidden band width of the active layer and the forbidden band width of the optical waveguide layer. An optical waveguide layer having a higher refractive index than the cladding layer is provided at a position shorter than the lower side and away from the ridge bottom surface in the cladding layer of the ridge portion toward the contact layer side. By providing a cap layer made of a semiconductor layer that does not contain aluminum with the same conductivity type as above, and by providing a contact layer on the cap layer, it is possible to reduce the optical power density in the active layer to enable high output operation, By adopting a structure in which the distance between the active layer and the optical waveguide layer is controlled not by etching conditions but by the crystal growth time, dimensional control for obtaining stable fundamental transverse mode oscillation is facilitated. It is a thing.

(Function) According to the present invention, a semiconductor laser suitable for high-power operation can be obtained in a transverse mode control structure having no regrowth interface containing Al in a region where current flows, and a stable fundamental transverse mode oscillation can be obtained. Size control can be performed easily.

(Example) Hereinafter, an example of the present invention and a reference example thereof will be described with reference to the drawings. FIG. 1 is a view showing a schematic structure of a semiconductor laser according to a reference example of the present invention. In the figure, 10 is an n-GaAs substrate, 11 is an n-GaAlAs cladding layer, and 12 is undoped Ga _1-x A
l _x As active layer, 13 and 14 are p-Ga _1-y Al _y As cladding layers, 15 is p-Ga _1-z Al _z As optical waveguide layer, 16 is n-Ga _1-w Al _w As current confinement Layer, 17 is a p-GaAs cap layer, 18 is a p-GaAs contact layer, 19 is an n-electrode, and 20 is a p-electrode. The magnitude relation of the Al composition ratio of each layer is as follows: y>z> x (1), which coincides with the magnitude relation of the forbidden band width.
The magnitude of the refractive index is reversed. The laser shown in FIG. 1 is manufactured as follows. First, an n-Ga _1-y Al _y As clad layer 11, a GaAlAs active layer 12, a p-type
GaAlAs cladding layer 13, p-GaAlAs optical waveguide layer 15, p-GaAl
After the As cladding layer 14 and the p-GaAs cap layer 17 are sequentially grown, a part of the cap layer 17, the cladding layer 14, the optical waveguide layer 15, and a part of the cladding layer 13 are removed by etching except for the central ridge. Next, an n-GaAlAs current confinement layer 16 is grown thereon. This current constriction layer can be formed by MOCVD growth, lift-off of the central ridge portion, or MOCVD selective growth using an SiO ₂ mask. After forming the current confinement layer, the ridge mask (resist,
The structure shown in FIG. 1 is manufactured by removing the SiO ₂ ), growing a p-GaAs contact layer 18 thereon, and finally forming electrodes 19 and 20.

In this laser, the regrowth on the ridge portion where the current flows is the growth on the p-GaAs cap layer 17, so that the regrowth on the crystal containing Al as shown in FIG. Good interface is obtained. In addition, the optical waveguide layer 15 allows the waveguide mode to exude outside the active layer during oscillation, and reduces the optical power density, which is suitable for high-output operation.

The beam divergence angle of the laser in the vertical direction is determined by the composition of each layer, the thickness of the active layer, the thickness of the optical waveguide layer, and the distance between the active layer and the optical waveguide layer (h in the figure). In the case of FIG. 3, h
Is difficult to control because it is determined by the etching conditions, whereas the structure shown in FIG. 1 is determined by the initial crystal growth conditions, so that precise dimensional control can be easily performed.

On the other hand, regarding the transverse mode confinement in the horizontal direction, the following two cases can be selected as a method of selecting the magnitude of the Al composition ratio w of the current confinement layer 16. The first example is a case where w <x (2), which is smaller than the forbidden band width of the current confinement layer, and the current confinement layer acts as a loss layer for the waveguide mode.
In this case, the loss waveguide type is the same as in FIG. The second example is the case where w> z (3). In this case, the forbidden band width of the current confinement layer is larger than the forbidden band width of the active layer. In addition, a laser having a low threshold value can be obtained because of a small loss. In this case, a refractive index guided type transverse mode control similar to that of FIG. 3 is realized. In this case, the effective refractive index difference is h and the distance h ′ between the active layer and the current confinement layer outside the ridge.
However, if the compositions of the current confinement layer and the p-cladding layer are close to each other, the value of h ', that is, the value determined by the etching conditions does not largely depend, and therefore, the stability of the basic transverse mode can be relatively easily determined. Can be obtained.
In particular, when the refractive index of the current confinement layer 16 is equal to the refractive index of the p-cladding layer, that is, when w = y (4), the effective refractive index outside the ridge does not depend on h '. Therefore, etching at the time of forming the ridge only needs to be stopped between the optical waveguide layer and the active layer, and precise control is not required.

FIG. 2 shows an embodiment of the present invention. In the figure,
30 is an n-GaAs substrate, 31 is an n-In _0.5 (Ga _{1 -y} Al _y ) _0.5 P cladding layer, 32 is an undoped In _0.5 (Ga _{1 -x} Al _x ) _0.5 P active layer, and 33 and 34 are p- In _0.5 (Ga _1-y Al _y ) _0.5 P cladding layer, 3
5 is p-In _0.5 (Ga _{1 -z} Al _z ) _0.5 P optical waveguide layer, 36 is n-Ga
_{A 1-w} Al _w As current confinement layer, 37 is a p-InGaP cap layer, 38 is a p-GaAs contact layer 39 is an n-electrode, and 40 is a p-electrode. The magnitude relationship between x, y, and z is the same as that of the equation (1). Further, it is also the same as in the reference example that the current confinement layer has a loss waveguide type depending on the composition. For example, when w = 0, the waveguide is a loss waveguide type, and when x = 0, y = 0.5z = 0.1, and w = 0.8, the waveguide is a lossless refractive index waveguide. Here, the current confinement layer is n-GaAlAs, but n-InGaAlP may be used.

In the above description, GaAlAs is used as a constituent material of the semiconductor laser.
Although the case of the system and the InGaAlP system has been described, the present invention is not limited to the above-described embodiment, and the InGaAsP system and the IGaAlP system can be used.
Other compound semiconductor materials such as nGaAlAs and GaAlSb may be used. It is also possible to use a p-type substrate as the substrate and reverse the conductivity type of each layer.

〔The invention's effect〕

According to the present invention, it is possible to obtain a laser that easily oscillates in the fundamental transverse mode with easy dimensional control during fabrication.

[Brief description of the drawings]

FIG. 1 is a view showing a reference example of the present invention, FIG. 2 is a view showing an embodiment of the present invention, and FIGS. 3 and 4 are views showing examples of a conventional transverse mode control semiconductor laser. 10,30,100,120 ... n-GaAs substrate, 11,101 ... n-GaAlA
s cladding layer, 12,102 ... undoped GaAlAs active layer, 13,
14,103,106 ... p-GaAlAs cladding layer, 15,105 ... p-
GaAlAs optical waveguide layer, 16, 36, 104 ... n-GaAlAs current confinement layer, 17, 125 ... p-GaAs cap layer, 18, 38, 107, 126 ...
... p-GaAs contact layer, 31,121 ... n-InGaAlP cladding layer, 32 ... undoped InGaAlP active layer, 122 ... undoped InGaP active layer, 33,34,123 ... p-InGaAlP cladding layer, 35 ... p-InGaAlP photoconductor Wave layer, 124 n-GaAs current confinement layer, 37 p-InGaP cap layer, 19, 39, 108, 127
…… n electrode, 20,40,109,128 …… p electrode.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Naoto Mogi 1 Toshiba Research Laboratory, Komukai Toshiba-cho, Kawasaki-shi, Kanagawa Prefecture (56) References JP-A-57-43487 (JP, A) Extended Abstract of The 18th Conference on Solid State Devices and Material Reals, Tokyo, 1986, PP. 153-156 Optical Technology Contact Vol. 25, No. 5, PP. 258-262 (1987) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/22

Claims (2)

(57) [Claims] 1. A ridge portion in which a thickness of a part of a clad layer opposite to a substrate is changed with respect to an active layer, and a current having a conductivity type different from that of the clad layer is formed on a clad layer other than the ridge portion. In a semiconductor laser having a constriction layer and a contact layer provided on the cladding layer and the current confinement layer, the forbidden band width of the current constriction layer is made larger than the forbidden band width of the active layer and the forbidden band width of the optical waveguide layer. An optical waveguide having a refractive index higher than that of the cladding layer at a position away from the bottom of the ridge in the cladding layer of the ridge portion toward the contact layer side, the upper side of the ridge portion being shorter in the stripe width direction of the ridge portion than the lower side thereof. A cap layer made of a semiconductor layer having the same conductivity type as that of the cladding layer and containing no aluminum, and a contact layer formed on the cap layer. A semiconductor laser, characterized in that digit. 2. The semiconductor laser according to claim 1, wherein a refractive index of said current confinement layer is substantially equal to a refractive index of said cladding layer.