JPH0724320B2 - Semiconductor laser and manufacturing method thereof - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lateral mode controlled semiconductor laser, and more particularly to a structure of a semiconductor laser capable of realizing a refractive index guide with good reproducibility and a manufacturing method thereof.

2. Description of the Related Art Conventionally, (AlGa) As based semiconductor lasers have been known as semiconductor lasers. In this (AlGa) As semiconductor laser,
It is said that the internal constricted channel stripe structure is effective for realizing a low threshold and lateral mode control.

FIG. 3 is a cross-sectional view of a (AlGa) As based semiconductor laser having an internal confined channel stripe structure according to a conventional example. In the figure, reference numeral 1 is an n-type GaAs substrate, on which n-type Al _x ′ Ga _1-x ′ As clad layer 2 is formed as a lower cladding layer and p-type Al _y ′ Ga is formed as an active layer by the first growth. _{The 1-} y′As layer 3, the p-type Al _x ″ Ga _1-x ″ As first cladding layer 4 forming a part of the upper cladding layer, and the n-type GaAs layer 5 as the current confinement layer are formed by, for example, a liquid phase epitaxial growth method (LPE). Method). Next, the thickness of the p-type Al _x "Ga _{1 -x} " As first cladding layer 4 is set to a value that does not have a light confining function, for example, 0.3 μm.
The trenches 6 are formed by etching off the n-type GaAs layer 5 in a stripe shape while leaving the above.

Next, by the second growth, a p-type Al _z Ga _1-z As second clad layer 7 which covers the groove 6 and constitutes an upper clad layer, and a p _- type GaAs contact layer 8 as a contact layer are formed by metal organic chemical vapor deposition. Method (MOVPE method).

Electrodes are attached to the p and n sides of the laminated structure formed as described above to form a semiconductor laser.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in such a structure, p-type Al _x "Ga _{1 -x} "
As When etching off the first clad layer 4, etching control must be performed so as to leave an extremely thin layer, and there is a problem that there is a large variation in the thickness of the remaining layer and poor reproducibility of semiconductor laser characteristics. It was

In general, the Al compound has a property that the crystal surface is easily oxidized, and it is necessary to increase the Al composition ratio when forming a semiconductor laser having a short oscillation wavelength. Therefore, p-type Al _x "Ga _1-x "
If the Al composition ratio x ″ of the As first cladding layer 4 is x ″> 0.4, an oxide film is likely to be formed on the surface, and crystal defects are introduced at the regrowth interface, resulting in deterioration of the characteristics of the semiconductor laser.

Therefore, an object of the present invention is to solve the above-mentioned problems at the same time, and to perform transverse mode control of a structure capable of reliably improving the characteristics and the reproducibility and reliability thereof at any oscillation wavelength (in the oscillation possible region). It is to provide a semiconductor laser and a manufacturing method thereof.

Means for Solving the Problems A semiconductor laser of the present invention comprises a GaAs substrate, a lower clad layer using an (AlGa) As layer, a double heterostructure including an active layer and an upper first clad layer, and (AlGaIn) It is to have a layer structure having an antioxidant layer made of a P layer and an internal current confinement layer having a higher Al composition ratio than the antioxidant layer.

A method for manufacturing a semiconductor laser according to the present invention is provided on a GaAs substrate with (Al
Ga) A lower clad layer using an As layer, a double heterostructure consisting of an active layer and an upper first clad layer, an antioxidation layer consisting of an (AlGaIn) P layer, and an internal current confinement layer having a higher Al composition than the antioxidation layer. A first crystal growth step of sequentially stacking
A step of forming a groove so that the (AlGaIn) P antioxidant layer is exposed, a step of performing thermal cleaning of the surface in a phosphorus atmosphere, and using at least the (AlGa) As layer covering the (AlGaIn) P antioxidant layer. In addition, the second crystal growth step of forming the upper second clad layer is included.

The (AlGaIn) P-based mixed crystal has the largest forbidden band width among the materials that lattice-match with the GaAs substrate, and even (GaIn) P with the smallest forbidden band width is 1.86 eV. It is larger than that of the AlGaAs active layer in the oscillating wavelength range of the semiconductor laser. Therefore, according to the configuration of the present invention, light absorption does not occur in the (AlGaIn) P oxidation prevention layer in the wavelength region where oscillation is possible, and the (AlGaIn) P internal current constriction layer is (AlGa) As.
The forbidden band width is larger than that of the first cladding layer, and the refractive index can be made small. Therefore, it becomes possible to provide a stable lateral mode controlled (AlGa) As based semiconductor laser with a refractive index guide.

Further, in the (AlGaIn) P mixed crystal, when the Al composition ratio is 0.35 or less,
The oxidizability can be sufficiently suppressed to form a regrown interface with few crystal defects. Furthermore, (GaIn) P and (AlGaI
n) P has mutual selective etching property. Therefore, according to the manufacturing method of the present invention, the etching stops at the surface of the (AlGaIn) P oxidation preventing layer, and the crystal defects are not generated at the regrowth interface without exposing the surface of the AlGaAs first cladding layer having a large Al composition ratio. Can be suppressed. The refractive index guide (AlG
a) The most important (AlG
a) The thickness of the As first cladding layer is controlled only by the growth conditions, and can be controlled extremely easily and accurately as compared with the conventional etching control, and the refractive index guide can be formed with good reproducibility.

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

FIG. 1 is a structural sectional view showing an embodiment of the semiconductor laser of the present invention.

In this embodiment, an n-type Al _x ′ Ga _1-x ′ As clad layer 2 (1 μm, x ′ = 0.
5), p-type Al _y ′ Ga _{1 -y} ′ As active layer 3 (0.1 μm) as an active layer
m, y ′ = 0.1), p-type Al that forms part of the upper cladding layer
_x ″ Ga _1-x ″ As first cladding layer 4 (0.3 μm, x ″ = 0.4),
And a p-type Al _x Ga _0.5-x In _0.5 P as an anti-oxidation layer formed on the surface of this double heterostructure.
Antioxidation layer 9 (0.05 μm, x = 0) and n-type Al _y Ga _0.5-y In _0.5 P internal current confinement layer 10 (0.5 μm, y) as an internal current confinement layer
= 0.2). 7 is a p-type Al _z Ga _1-z As second cladding layer (2 μm, z = 0.
5) and 8 are p-type GaAs contact layers (1 μm) as contact layers, which are formed so as to cover the trenches 6.

In the semiconductor laser of this embodiment, p-type Al _x "Ga _1-x "
As the first clad layer 4 does not have a light confinement function.
The film thickness is precisely controlled to 3 μm.

In the semiconductor laser of this example, p-type Al _x Ga _0.5-x In
_No light absorption occurs in the _0.5 P anti-oxidation layer 9, and n-type Al _y Ga _0.5-y
In _0.5 P Internal current confinement layer 10 has a refractive index of p-type Al _x ″ Ga _1-x ″ As
Since it is smaller than that of the first cladding layer, a good refractive index guide can be formed, and therefore stable transverse mode oscillation is possible.

Next, a method of manufacturing the semiconductor laser of the present invention will be described with reference to the semiconductor laser manufacturing process diagram of FIG.

Using the MOVPE method, an Al _x ′ Ga _1-x ″ As clad layer 2 (1 μm, x ′ = 0.
4), p-type Al _y ′ Ga _{1 -y} ′ As active layer 3 (0.1
μm, y ′ = 0.1), p-type that forms part of the upper cladding layer
Al _x ″ Ga _1-x ″ As First clad layer 4 (0.3 μm, x ″ = 0.
5), p-type Al _x Ga _0.5-x In _0.5 P antioxidant layer 9 (0.05 μm, x = 0.5) as an antioxidant layer, and n-type internal current confinement layer
Al _y Ga _0.5-y In _0.5 P Internal current confinement layer 10 (0.5 μm, y = 0.2)
A was sequentially laminated. Triethyl gallium, trimethyl aluminum, trimethyl indium as source gas,
Arsine and phosphine were used, hydrogen selenide was used as the n-type dopant, and dimethylzinc was used as the p-type dopant. The growth conditions were 700 ° C. and the furnace pressure was 100 Torr.

Next, form a 5μm wide stripe window by ordinary photolithography and perform etching in sulfuric acid (50 ° C).
The groove 6 was formed. Since it has etching selectivity in sulfuric acid (50 ° C) and the etching rate of Ga _0.5 In _0.5 P is extremely slower than that of Al _0.2 Ga _0.3 In _0.5 P, it is almost p-type.
The etching stops on the surface of the Al _x Ga _0.5-x In _0.5 P oxidation preventing layer 9 (b). At this time, the p-type Al _x G exposed on the surface
Since it is the a _0.5-x In _0.5 P antioxidant layer 9 and the n-type Al _y Ga _0.5-y In _0.5 P internal current confinement layer 10, thermal cleaning is performed in a phosphine atmosphere in the MOVPE apparatus. The temperature at this time is 65
The temperature was 0 ° C. Following thermal cleaning, the p-type Al _z Ga _1-z As second clad layer 7 constituting the upper clad layer 7 is formed.
(2 μm, z = 0.5), p-type GaAs layer 8 as contact layer
(1 μm) were sequentially laminated (c). Finally, electrodes were attached to the p and n sides to form a semiconductor laser.

According to the method for manufacturing the semiconductor laser of this embodiment, Ga _0.5 I
By utilizing the etching selectivity of n _0.5 P and Al _0.2 Ga _0.3 In _0.5 P, p-type Al _x ″ Ga _1-x ″ As with a large Al composition ratio
Since the surface of the first cladding layer 4 is not exposed and there is almost no variation in the film thickness due to etching, a semiconductor laser with good reproducibility and high reliability can be manufactured.

As described above, the semiconductor laser in which the active layer is Al _0.1 G _0.9 As has been described in the embodiments, but the Al composition ratio may be any, and the active layer can be sufficiently applied in the Al composition ratio in the direct transition region. Although the substrate is an n-type GaAs substrate, a p-type GaAs substrate may be used. In that case, the conductivity types of other layers may be changed accordingly. Furthermore, the present invention can also be applied to an AlGaAs-based quantum well laser.

EFFECTS OF THE INVENTION As is clear from the above description, the structure and manufacturing method of the semiconductor laser of the present invention can suppress the generation of crystal defects at the regrowth interface and facilitate the control of the film thickness by etching, so that the device characteristics and It has the effect of improving reproducibility and reliability and is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the structure of the semiconductor laser of the present invention, FIG. 2 is a process diagram for explaining an embodiment of the method of manufacturing the semiconductor laser of the present invention, and FIG. It is sectional drawing of a semiconductor laser. 1 ... n-type GaAs substrate, 2 ... n-type Al _x ′ Ga _1-x ′ As clad layer, 3 ... p-type Al _y ′ Ga _1-y ′ As active layer, 4 ... p-type Al
_x ″ Ga _1-x ″ As first cladding layer, 5 ... n-type GaAs layer, 6 ...
… Groove, 7 …… p-type Al _z Ga _1-z As second cladding layer, 8 …… p
Type GaAs contact layer, 9 ... p-type Al _x Ga _0.5-x In _0.5 P oxidation prevention layer, 10 ... n-type Al _y Ga _0.5-y In _0.5 P internal current confinement layer.

Claims (2)

[Claims] 1. An (AlGa) As layer as an active layer on a GaAs substrate of the first conductivity type, and the active layer has a first conductivity type (AlGa) As cladding layer and a second conductivity type (AlGa) having different composition ratios. As having a double hetero structure sandwiched by a first cladding layer, a second conductivity type (Al _x GaIn) P oxidation prevention layer and a first conductivity type (Al _y GaIn) P internal current constriction layer above the active layer. (Where 0 ≦ x
<Y ≦ 0.5) A semiconductor laser. 2. An (AlGa) As layer as an active layer on a GaAs substrate of the first conductivity type, the active layer having the first conductivity type (Al) having a different composition ratio.
Ga) As clad layer and second conductivity type (AlGa) As first clad layer sandwiched double heterostructure and second conductivity type (Al _x GaI
n) a P oxidation preventing layer and a first conductivity type (Al _y GaIn) P internal current confinement layer are sequentially formed (where 0 ≦ x <y ≦ 0.5), a first crystal growth step, and the second conductivity type. An etching step of forming a groove so that the (Al _x GaIn) P oxidation preventing layer is exposed, a step of thermally cleaning the surface in a phosphorus atmosphere, and a step of covering the second conductivity type (Al _x GaIn) P oxidation preventing layer. And a second crystal growth step for forming at least a second conductivity type (AlGa) As second cladding layer.