JPH0334595A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PURPOSE:To perform high output with a single transverse mode and stable operations for a long time by allowing a semiconductor laser to be equipped with a buried layer covering side faces of an active layer and a photoabsorption layer which absorbs light leaking out from the neighbourhood of both ends of the active layer in the semiconductor laser having double heterostructure which makes (AlxGa1-x) InP act as the active layer and furthermore, (AlyGa1-y) InP act as a clad layer on a GaAs substrate, thereby making the buried layer have a prescribed composition. CONSTITUTION:An n-type AlGaInP clad layer 2, a GaInP active layer 3, a p-type AlGaInP clad layer 4, and a p-type GaAs cap layer 5 are formed in order on an n-type GaAs substrate 1. Double heterostructure is made up to have a forward mesa like ridge having the width of 6mum and a thin high resistive AlGaAs buried layer 6 and a high resistive GaAs photoabsorption layer 7 are formed at the side faces of the ridge. As the side faces of the GaInP active layer 3 have forbidden band widths broader than those of GaInP and are covered with the AlGaAs buried layer 6 that has a low refractive index but has a high resistance, electric current together with light are confined in the GaInP active layer 3. However, as the ridge is formed into the forward mesa like shape, the neighborhood of both ends of the active layer 3 has a thin p-type AlGaInP clad layer 4 and then, lower slopes of light distribution are placed on the high resistive GaAs photo-absorption layer 7. Its photoabsorption, therefore, enables a higher order transverse mode to perform suppressed single transverse mode oscillations, even though its ridge width becomes wider.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to visible light semiconductor lasers that can be used for optical communication of information, optical erasing, recording, and reproduction, etc., and particularly relates to semiconductor lasers and semiconductor lasers suitable for manufacturing by the MOVPE method. It relates to its manufacturing method.

Conventional technologyDigital audio disc 0 as a light source for optical disk files, information processing equipment such as laser printers
．． There is a demand for a 6 μm band AIGa InP/GaAs visible light semiconductor laser. A conventional semiconductor laser has a structure as shown in FIG. 3, for example. This buried structure has a structure in which the sides of a striped active layer are buried with a semiconductor layer with a large forbidden band width, and Ga is used as a semiconductor laser with a single transverse mode, low value, and high efficiency.
It has been put into practical use in the InAsP/InP system, and is the most popular type of refractive index waveguide structure. The case of FIG. 3 in which the conventional buried structure is applied to an AlGa1nP/GaAs visible light semiconductor laser will be described below. l is n-GaAs base Kaede 2 is n-AIGaInp
Cladding layer 3 is GaInP activity #4 is p-AlGa
1 nP cladding 5 is a P-GaAs cap 11 is a high resistance AlGaAs embedded 9 and 10 are each n
, is the p-side electrode. The above structure is formed by the MOVPE method. In this structure, high resistance AlG
Since the aAs buried layer 11 has a wider forbidden band and a lower refractive index than the GaInP active layer 3, current flows only through the GaInP active layer and light is trapped due to the difference in refractive index in the lateral direction, but the invention solves this problem. However, in such a buried structure, in order to obtain single transverse mode oscillation, it is necessary to reduce the active layer width to 1 to 2 μm.AlGa1nP quaternary mixed crystal has a high material resistance, so it is not active. If the layer width is narrowed, the series resistance increases and the operating voltage increases, which is a problem.
At the same time, the optical density at the end face of the resonator increases, making it difficult to operate at a high output and reducing the t. Therefore, the purpose of the present invention is to widen the width of the active layer to eliminate the above drawbacks at the same time, and to achieve high output in a single transverse mode. 9. Good AIG capable of stable operation for long periods of time
The object of the present invention is to provide an aInP/GaAs visible light semiconductor laser with good reproducibility.

Means for Solving the Problems In order to solve the above-mentioned problems, the semiconductor laser of the present invention and its manufacturing method skillfully utilize the characteristics of the MOVPE method.
lns, sP as active layer and L(A1yGa+-y)s, 5
In a semiconductor laser having a double heterostructure (where X and y are O≦X<y≦1) with lns and sP as cladding layers, the double heterostructure is formed into a striped mesa structure, and the double heterostructure is embedded to cover the side surface of the active layer. The buried layer is a semiconductor layer having a wider forbidden band width and a lower refractive index than the active layer, and a light absorption layer that absorbs light seeping out from near both ends of the active layer. The layer is characterized by being a semiconductor layer having a narrower bandgap and a larger refractive index than the active layer, and its manufacturing method includes forming (A1xGa+-x)m, s Inn, sP on a GaAs substrate as an active layer. ,, (A1yGa+-y)s, sln@
, a double heterostructure with sP as the cladding layer (here, X
and y is O≦X<y≦1); a step of etching the double heterostructure into a striped mesa structure; a buried layer covering the side surface of the active layer; and a second crystal growth step of continuously forming a light absorption layer that absorbs light seeping out from the vicinity of both ends of the active layer. Layer The light absorption layer is characterized in that it is a semiconductor layer having a narrower forbidden band width and a higher refractive index than the active layer. In this case, since the AlGaAs buried layer is thin, there is no cladding layer thick enough to confine light at both ends of the active layer, so the base of the light distribution falls on the light absorption layer.

Function The function of the present invention can be explained as follows. That is, since the active layer is surrounded by a low refractive index AlGaAs buried layer, light is confined in the active layer. However, at both ends of the active layer, the buried layer is sufficiently thin so that the base of the light distribution covers the light absorption layer.

The waveguiding loss for higher-order transverse modes is larger than the waveguiding loss of the active layer for the fundamental transverse mode.
Single transverse mode oscillation can be maintained even if the width of the active layer is widened, and since the width of the active layer can be widened, the series resistance can be reduced and the operating voltage can be reduced. Furthermore, the optical density on the resonator surface can be reduced, allowing high output operation. Since the stripe width of the ridge structure can be increased by the width of the active layer, manufacturing is facilitated.

EXAMPLE Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a schematic cross section of the semiconductor laser of the present invention; FIG. 2 is a process diagram showing the manufacturing method. The structure of the semiconductor laser of the present invention is as shown in FIG.
-AlGa1np cladding layer 2, GaInP active layer 3,
A p-AIGaInP cladding layer 4 and a P-GaAs cap layer 5 are sequentially formed. Double heterostructure is width 6
It has a mesa-like ridge structure with a diameter of μm, and a thin high-resistance AlGaAs buried layer 6 and a high-resistance GaAs ridge structure are formed on its side surfaces.
7 for light absorption. In this structure, G
Since the sides of the a I nPP layer 3 are covered with a high resistance AlGaAs buried layer 6 having a wider forbidden band width and a lower refractive index than GaInP, both current and light are confined within the Ga InP active layer 3 . However, the ridge part is mesa-shaped (IT
O > stripe), so the Ga I nP active layer 3
Near the ends, the p-AlGa1nP cladding layer 4 is thin;
The base of the light distribution is made of high-resistance GaAs light absorption.This light absorption enables single transverse mode oscillation with suppressed high-order transverse modes even if the ridge width is wide.At the same time, the series resistance is 6Ω or less. Laser oscillation with a low operating voltage and a threshold current of 50 mA was achieved.The optical density at the cavity end face was reduced and a maximum oscillation optical output of 30 mW was obtained.The astigmatism difference was measured with this structure. 1. It is small, less than 4 μm, and has almost no output dependence. The method for manufacturing the semiconductor laser of the present invention may be as follows.
As shown in FIG.
np cladding layer 2, GaInP active layer 3, p-AIGa
The InP cladding layer 4 and the P-GaAs cap layer 5 are epitaxially grown in sequence by the MOVPE method. Next, the SiO2 film 8 is placed on the P-GaAs cap layer 5. After forming 6 μm stripes in the <ITO> direction, the SiO2 film is grown. n by chemical etching using 8 as a mask.
Although the ridge structure is formed by removing up to the -AIGaInp layer 2, the ridge portion becomes a mesa shape. (Fig. 2B) After that, using the above 5i (h layer 8 as a selective mask), a high resistance AlGaAs buried layer 6 (A
For example, IAs composition is 0.6) and 0.2μH high resistance Ga.
The As light absorbing light absorbing layer 7 is sequentially grown epitaxially by the MOVPE method so that it becomes flat 7) c, (Figure 2 C)
AIGa containing active AI can be obtained using MOV P E method.
Good high A IAs group 0 precepts lGaAs on Inp layer
The layer can be regrown, and the thickness of the side surface of the Ga1nP active layer 3 becomes a desired value with good reproducibility. After removing the L5iOa film 8 and forming a slit-like stripe window, t't and AuG are used as the n-side electrode 9 and the p-side electrode IO, respectively.
Deposit e/Au and Ti/Pt/Au. Thereafter, a resonator end face is formed by cleaving. Finally, it is cut to a predetermined size, mounted, and packaged to obtain a semiconductor laser (Figure 2D).With this manufacturing method, a ridge structure can be formed with good reproducibility because the stripe width is wide. In the above explanation, AlGa1nP/GaAs
Regarding the case of forming a double heterostructure of GaIn
IJ<, AIGaInP explained using P active layer
There is no problem even if the active layer is an active layer or an active layer with a quantum well structure.Also, the present invention can also be applied to the case where layers of the opposite conductivity type to those in the above embodiments are grown on a P-GaAs substrate. Needless to say, 1 Satoshin The buried layer and light absorption layer are high resistance layers, but if the structure allows current confinement, there is no need to use high resistance layers. Although it is possible to apply the growth method or other vapor phase growth methods, the ridge structure is here a mesa-like structure (as mentioned above, the effect of the invention is limited to this, the number of active layers according to the present invention is The width can be made wider than the conventional buried structure semiconductor laser, so
It is possible to reduce the operating voltage and optical density, and it is easy to obtain a high-power, single transverse mode AIGaInP/GaAs visible light semiconductor laser, which has great practical effects as a light source for optical information processing devices such as optical disks.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a semiconductor laser according to an embodiment of the present invention.
The figure shows the manufacturing method of the semiconductor laser of the same example. The manufacturing process is as follows: Figure 3 is a schematic diagram of a conventional buried structure semiconductor laser. 1...n-GaAs substrate 2...n-AIG
aInp cladding layer, 3...GaInP active layer,
4----p-AIGaInP cladding layer, 5...
P-GaAs cap 6...High resistance AlGaA
s embedded 7... High resistance GaAs light absorption #8.
...5inspL 9...n-side type K 10...
...p-side electrode 11...high resistance AlGaAs embedded phosphor

Claims (4)

[Claims] (1) On the GaAs substrate (Al_XGa_1_-_X)
InP is used as the active layer, (Al_yGa_1_-_y)I
In a semiconductor laser having a double heterostructure (where X and y are 0≦X<y≦1) with nP as a cladding layer, the double heterostructure is formed into a striped mesa structure, and a buried layer covers the side surface of the active layer. and a light absorption layer that absorbs light seeping out from the vicinity of both ends of the active layer, the buried layer is a semiconductor layer having a wider forbidden band width and a lower refractive index than the active layer, and the light absorption layer A semiconductor laser characterized in that the semiconductor layer is a semiconductor layer having a narrower forbidden band width and a higher refractive index than the active layer. (2) On the GaAs substrate (Al_XGa_1_-_X)
InP is used as the active layer, (Al_yGa_1_-_y)I
A first crystal growth step of forming at least a double heterostructure (where X and y are 0≦X<y≦1) with nP as a cladding layer, and etching the double heterostructure into a striped mesa structure. and a second crystal growth step of continuously forming a buried layer that covers the side surface of the active layer and a light absorption layer that absorbs light seeping from near both ends of the active layer, is a semiconductor layer having a wider forbidden band width and lower refractive index than the active layer, and the light absorption layer is a semiconductor layer having a narrower forbidden band width and higher refractive index than the active layer. . (3) Claims 1 and 2, characterized in that the buried layer is Al_aGa_1_-_aAs and the light absorption layer is Al_bGa_1_-_bAs (where a and b are 0≦b<a≦1). Semiconductor laser described in section. (4) The semiconductor laser according to claim 2, wherein the crystal growth step is formed by a crystal growth technique in a thermal non-equilibrium state such as metal organic vapor phase epitaxy or molecular beam growth. manufacturing method.