JP2003060312A - Semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the high-output characteristic of a 0.7-1.2 μm semiconductor laser element formed on a GaAs substrate, by suppressing the resistance of the element. SOLUTION: The semiconductor laser element is constituted, by successively forming an n-type Alz1 Ga1-z1 As lower clad layer 3, n-type Alw Ga1-w As layer 4, n- or i-type Inx Ga1-x Asy P1-y lower optical waveguide layer 5 lattice-matched with GaAs, active layer 6, p- or i-type Inx Ga1-x Asy P1-y upper optical guide layer 7 lattice-matched with GaAs, p-type Alw Ga1-w As layer 8, p-type Alz1 Ga1-z1 As upper clad layer 9, p-type GaAs contact layer 11, and SiO2 film having a stripe-like current injection opening on an n-type GaAs substrate 1 and providing a p-side electrode 13 on the contact layer 11 and an n-side electrode 14 on the rear surface of the substrate 1. The Alw Ga1-w As layers 4 and 8 have band gaps E, which are smaller than those Ec of the clad layers 3 and 9 and larger than those Ew of the optical waveguide layers 5 and 7 (Ew<E<Ec) and have the same refractive index N as those Nw of the optical waveguide layers 5 and 7 (N=Nw).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly, to a 0.7-1.2 formed on a GaAs substrate.
The present invention relates to a μm band semiconductor laser device.

[0002]

2. Description of the Related Art Conventionally, High Reliability in 0.8- ■ m High Power InGaAsP described in SPIE Vol. 3628, pp.29-37
/ InGaP / AlGaAs Laser Diodes with A Broad Waveguide
In a semiconductor laser equipped with an InGaAsP quantum well active layer formed on a GaAs substrate,
It has been reported that high reliability can be obtained by providing an optical waveguide layer made of InGaP and making the cladding layer AlGaAs. Further, in the above document, it is also reported that by increasing the thickness of the optical waveguide layer, the peak light intensity in the active layer can be reduced and the reliability is improved.

[0003]

However, in the structure reported in the above document, the band offset at the InGaP / AlGaAs hetero interface is large, so that a substantially spike-like barrier layer exists at this interface. However, there is a problem that the element resistance is high. Therefore, optical waveguide layer thickness 0.22μm, 50μm stripe width, resonator length 750?
In the semiconductor laser device having the above structure of μm, thermal saturation occurs at an optical output near 1 W.

The present invention has been made in view of the above circumstances, and in a 0.7-1.2 μm semiconductor laser formed on a GaAs substrate, suppresses device resistance due to the presence of a spike-like barrier layer formed at the hetero interface. An object of the present invention is to provide a semiconductor laser device having improved high output characteristics.

[0005]

A semiconductor laser device of the present invention comprises an AlGaAs lower clad layer, a lower optical waveguide layer made of InGaAsP or InGaP lattice-matched to GaAs, on a GaAs substrate.
In a semiconductor laser device comprising an active layer, an upper optical waveguide layer made of InGaAsP or InGaP lattice-matched to GaAs, an AlGaAs upper cladding layer, and a GaAs contact layer in this order, the lower and upper optical waveguide layers are the active layers. A band gap larger than the band gap between the lower cladding layer and the lower optical waveguide layer. A first AlGaAs layer having a refractive index of a size between the two or a refractive index substantially the same as the refractive index of the lower optical waveguide layer is provided, and a band of both is provided between the upper cladding layer and the upper optical waveguide layer. A second AlGaAs having a band gap having a size between the gaps and having a refractive index between the refractive indices of the two or substantially the same as the refractive index of the upper optical waveguide layer. The is characterized in that it comprises.

In the above semiconductor laser device, at least a part of the first AlGaAs layer on the side of the lower clad layer has a band gap from the band gap of the lower clad layer to the band gap of the first AlGaAs layer. Is replaced with a first AlGaAs composition gradient layer that changes continuously or stepwise, and at least a part of the second AlGaAs layer on the side of the upper clad layer has a band gap of the band gap of the upper clad layer. To the bandgap of the second AlGaAs layer continuously or stepwise
The AlGaAs composition gradient layer may be replaced.

That is, the semiconductor laser device of the present invention is
First and second layers are provided between the lower clad layer and the lower optical waveguide layer, and between the upper clad layer and the upper optical waveguide layer, respectively.
With an AlGaAs layer, a first and a second AlGaAs composition gradient layers instead of the first and the second AlGaAs layers, or a first and a second AlGaAs layers and a first and a second AlGaAs layer. Any of those provided with the AlGaAs composition gradient layer at the same time may be used.

Further, a third AlGaAs composition gradient layer having a band gap that continuously or stepwise changes from the GaAs substrate to the lower clad layer is provided between the GaAs substrate and the lower clad layer. A fourth AlGaAs composition gradient layer having a band gap that continuously or stepwise changes from the upper clad layer to the GaAs contact layer between the upper clad layer and the GaAs contact layer. desirable.

In the above semiconductor laser device, the active layer is formed of In _x1 Ga _1-x1 As with 0 ≦ x1 ≦ 0.4 and 0 ≦ y1 ≦ 0.6.
A quantum well active layer containing _1−y1 P _y1 is desirable.

The lower and upper optical waveguide layers are made of InGa.
It is desirable to provide barrier layers made of P and made of InGaAsP having a bandgap larger than that of the active layer as upper and lower layers of the active layer.

A refractive index guiding mechanism is provided, in which a current blocking layer is provided on the active layer, in which a groove is formed so as to form a current path to the active layer, that is, an internal current constriction. A semiconductor laser device having a structure may be used.

On the active layer, at least a part from both sides to the end of the passage is removed in a groove shape on both sides of a region serving as a passage of a current to the active layer, and between the removed regions. A semiconductor laser device having a refractive index guiding mechanism provided with a ridge-shaped current passage, that is, a ridge structure may be used.

The width of the current passage is 1.5 μm or more and 4 μm
If it is less than, the equivalent refractive index step is 2 × 10 ^{−3 to} 7 × 10 ^−3.
The following is desirable.

When the width of the current passage is 4 μm or more, the equivalent refractive index step is preferably 2 × 10 ⁻³ or more.

In the case of the internal current confinement structure, the equivalent refractive index step is defined as na which is the equivalent refractive index at the oscillation wavelength in the laminating direction of the region where the current constricting layer exists, and oscillation in the laminating direction in the current path. Assuming that the equivalent refractive index at the wavelength is nb, the equivalent refractive index difference Δn is defined by nb-na. In the case of a ridge structure, if the equivalent refractive index at the oscillation wavelength in the stacking direction at the bottom portions on both sides of the ridge is nA and the equivalent refractive index at the oscillation wavelength in the stacking direction at the ridge is nB, then the equivalent The refractive index step ΔN is defined by nB-nA.

[0016]

According to the semiconductor laser device of the present invention, both are provided between the cladding layer and the optical waveguide layer, that is, at the hetero interface between the AlGaAs layer and the InGaAsP layer or the InGaP layer, which has caused a large device resistance. The first or second AlGaAs layer having a bandgap of a size between the two bandgap and having a refractive index substantially the same as the refractive index of the optical waveguide layer is generated at the hetero interface. Since the spike-shaped barrier height can be reduced and the element resistance can be reduced, thermal saturation is suppressed up to a high output and reliability is high.

At the hetero interface, first and second AlGaAs are formed.
When the graded layer is provided, the AlGaAs layer has a higher refractive index when the band gap is reduced by changing the Al composition, but the composition change is caused by the band gaps of the first and second AlGaAs layers.
The composition that becomes the bandgap of the layer, that is, the maximum refractive index of this AlGaAs layer is the same as the refractive index of the optical waveguide layer so that it does not become larger than the refractive index of the optical waveguide layer made of InGaAsP or InGaP With this, it is possible to obtain a good semiconductor laser device that does not adversely affect the optical confinement.

Furthermore, a third band gap in which the band gap changes continuously between the GaAs substrate and the lower clad layer and between the upper clad layer and the GaAs contact layer, respectively.
If the AlGaAs composition gradient layer and the fourth AlGaAs composition gradient layer are provided, a semiconductor laser device having a further reduced device resistance can be obtained.

If the active layer is a quantum well active layer containing In _x1 Ga _1-x1 As _1-y1 P _y1 with 0 ≦ x1 ≦ 0.4 and 0 ≦ y1 ≦ 0.6, 700 <λ <1200 (nm) It is possible to obtain a highly reliable semiconductor laser device having a peak wavelength in the range.

Further, when InGaP is used as the optical waveguide layer, a barrier layer made of InGaAsP having a bandgap larger than that of the active layer is provided as upper and lower layers of the active layer to precisely control the heterojunction interface, High quality crystal growth can be performed.

In the case of a semiconductor laser device having a refractive index guiding mechanism, the width of the current path is set to 1.5 μm or more and less than 4 μm, and the equivalent refractive index step is set to 2 × 10 ⁻³ or more and 7 × 10 ⁻³ or less. As a result, fundamental transverse mode oscillation can be obtained up to high output.

Further, the width of the current passage is set to 4 μm or more,
By setting the equivalent refractive index step to 2 × 10 ⁻³ or more, it is possible to obtain highly reliable laser light with low noise even in multimode.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a shape (a) in a cross section perpendicular to the waveguiding direction, a bandgap energy profile (b), and a refractive index profile (c) in the stacking direction of the semiconductor laser according to the first embodiment of the present invention. It is shown.

As shown in FIG. 1A, this semiconductor laser
The device consists of n-Al on n-GaAs substrate 1. _z1Ga_1-z1As lower club
Dead layer 3, n-Al_wGa_1-wAs layer 4, n that lattice-matches GaAs
Ruiha i-In_xGa_1-xAs_yP_1-yLower optical waveguide layer 5, active layer 6, G
p or i-In lattice matched to aAs_xGa_1-xAs_yP_1-yUpper light
Waveguide layer 7, p-Al_wGa_1-wAs layer 8, p-Al_z1Ga_1-z1As upper club
Pad layer 9, p-GaAs contact layer 11, stripe current
SiO with injection openings₂With a membrane 12 on the contact layer 11
It is equipped with a p-side electrode 13 and an n-side electrode 14 on the substrate 1 side.
is there.

As shown in FIGS. 1B and 1C, the Al _w Ga _1-w As layers 4 and 8 are the band gaps Ec of the cladding layers 3 and 9 made of Al _z1 Ga _{1- z1} As. And an optical waveguide layer 5 made of In _x Ga _1-x As _y P _1-y, having a band gap E (Ew <E <Ec) between the band gaps Ew of the optical waveguide layers 5 and 7, and , 7 which is substantially the same as the refractive index Nw (N = N
w) and the Al _w Ga _1-w As layers 4 and 8
By providing the Al _z1 Ga _1-z1 As layers 3 and 9 and In _x Ga _1-x
The device resistance can be reduced by suppressing the barrier height when the As _y P _1-y layers 5 and 7 are directly joined. For example,
When In _0.49 Ga _0.51 P with x = 0.49, y = 0 is used as the In _x Ga _1-x As _y P _1-y optical waveguide layers 5 and 7, Al _w having a refractive index substantially equal to this refractive index is used. The composition range of Ga _1-w As is 0.5 ≦ w ≦ 0.54. The refractive index of the Al _w Ga _1-w As layers 4 and 8 does not necessarily have to be substantially the same as the refractive index of the optical waveguide layer, and is larger than the refractive index Nc of the cladding layers 3 and 9, The refractive index is less than or equal to Nw, that is, Nc <N ≦ Nw.

Instead of the Al _w Ga _1-w As layer 4, the band gap of the lower optical waveguide layer 5 is changed from the band gap of the AlGaAs lower cladding layer 3 toward the band gap of the InGaAsP lower optical waveguide layer 5. Al whose composition has been changed so as to continuously decrease until the composition has a refractive index substantially the same as the refractive index Nw of
_{A w2} Ga _1-w2 As compositionally graded layer is provided, and instead of the Al _w Ga _1-w As layer 8, its band gap is from the AlGaAs upper cladding layer 9.
Al _w3 Ga _1-w3 As composition gradient in which the composition is changed toward the InGaAsP upper optical waveguide layer 7 so that the composition has a refractive index substantially equal to the refractive index Nw of the upper optical waveguide layer 7. A semiconductor laser device having layers and having a bandgap profile shown in FIG. 2A may be used.

Further, as shown in the band gap profile in FIG. 2B, the first AlGaAs layer and the second AlGa layer are formed.
Part of the As layer is Al _w2 Ga _1-w2 As composition gradient layer and Al _w3 Ga _1-w3
A semiconductor laser device in which the As composition gradient layer is replaced may be used. In addition, the band gap is not continuous and is shown in FIG.
It may be provided with a graded AlGaAs composition gradient layer as shown in FIG.

As the active layer 6, In _x1 Ga _1−x1 As
_{By using 1−y1} P _y1 (0 ≦ x1 ≦ 0.4, 0 ≦ y1 ≦ 0.6) and controlling the composition ratio, a semiconductor laser device having a peak oscillation wavelength in the range of 700 <λ <1200 (nm) is obtained. can do. Further, the active layer 6 may be composed of any of lattice matching system, one having a compressive strain, and one having a tensile strain.

Further, as shown in FIG. 3, as a layer above and below the active layer 6, InGa having a band gap larger than that of the active layer 6 is used.
A semiconductor laser device including the barrier layers 16 and 17 made of AsP may be used. At this time, the barrier layer may be lattice-matched, compressively strained, or tensilely strained.

FIG. 4 shows a semiconductor laser device according to the second embodiment.
Cross-sectional view of child (a) and energy gap in stacking direction
A profile (b) is shown. As shown in FIG.
The body laser element is similar to the semiconductor laser element shown in FIG.
N-GaAs substrate 1 and n-Al_z1Ga _1-z1As lower clad layer 3
The band gap of the GaAs substrate 1 is
Up to the band gap of the lower cladding layer 3
N-Al changing to_w1Ga_{1- w1}Equipped with As composition graded layer 2, p-Al_z1
Ga_1-z1As upper clad layer 9 and p-GaAs contact layer 11
The band gap of the GaAs contact layer 11 is
From the gap to the band gap of the upper clad layer 9
N-Al that changes continuously_w4Ga_1-w4With As composition graded layer 10
It is a thing. Thus, the layers 3 and 9 made of AlGaAs and Ga
Providing a composition gradient layer between the layers 1 and 11 made of As
The element resistance can be further reduced, and the element
Reliability can be improved.

Next, a method of manufacturing the semiconductor laser device according to the second embodiment of the present invention shown in FIG. 3A will be described.

First, the n-Al _w1 Ga _1-w1 As composition gradient layer 2 and the n-Al _z1 Ga _{1-z1 are formed} on the n-GaAs substrate 1 by the metal organic chemical vapor deposition method.
As lower clad layer 3 (0.57 ≦ z1 ≦ 0.8), n-Al _w2 Ga _1-w2 As
Compositionally graded layer 4, n or i-In _0.49 Ga _0.51 P lower optical waveguide layer 5, In _x1 Ga _1-x1 As _1-y1 P _y1 quantum well active layer 6 (0 ≦ x1 ≦ 0.
4,0 ≦ y1 ≦ 0.6, thickness: 3 to 20 nm), p or iI
n _0.49 Ga _0.51 P upper optical waveguide layer 7, p-Al _w3 Ga _1-w3 As composition gradient layer 8, p-Al _z1 Ga _1-z1 As upper cladding layer 9, p-Al _w4 Ga _1-w4
An As composition gradient layer 10 and a p-GaAs contact layer 11 are laminated. Subsequently, forming a SiO ₂ film 12 by conventional lithography, <011> direction to remove the SiO ₂ film 12 of stripe area having a width of about 50 [mu] m, to form a p-side electrode 13, the subsequent polishing of the substrate 1 Then, the n-side electrode 14 is formed on the polished surface.
Then, one of the resonator surfaces formed by cleaving the sample is coated with a high reflectance and the other is coated with a low reflectance, and the semiconductor laser element is formed into chips.

As shown in FIG. 3B, p-Al _w4 Ga _1-w4 As
The compositionally graded layer 10 and the n-Al _w1 Ga _1-w1 As compositionally graded layer 2 are configured so that the band gap is continuously equal to the band band gap of the GaAs layer from the cladding layer, and the thickness is within 0.3 μm. And Further, in place of Al _w2 Ga _1-w2 As gradient composition layer 4 and the Al _w3 Ga _1-w3 As composition gradient layer 8, an In _{0. 49}
Al _z2 G whose refractive index is almost the same as that of the optical waveguide layer made of Ga _0.51 P
An a _{1-z 2} As optical waveguide layer (0.5 ≦ z 2 ≦ 0.54) may be provided instead. Also in this case, there is an effect of reducing the element resistance.

The stripe width of the above structure is 50 μm, and the resonator length is 7
An element having a thickness of 50 μm was compared with an element having the same structure but having no composition gradient layer. The device resistance of the device without composition gradient layer
While it was 0.6Ω, the element resistance of the element of the present embodiment having the composition gradient layer was 0.4Ω, and it is clear that the element resistance was obviously reduced by providing the composition gradient layer. Became.

In the above embodiment, In _x1 Ga _1-x1
As _1-y1 P _y1 quantum well An In _x3 Ga _1-x3 As _1-y3 P _y3 barrier layer (about 20 nm or less) having a band gap larger than that of the active layer may be provided adjacent to the active layer 6 above and below. The barrier layer may be lattice matched, compressive strain, tensile strain. By forming InGaAsP-based quantum wells from the InGaP-based optical waveguide layer through the InGaAsP-based barrier layer, the source gas switching time at the heterojunction interface can be shortened and the source gas can be controlled with high accuracy. Therefore, high quality crystal growth can be performed.

In the above embodiments, the structure having the oxide film stripe structure is shown, but a semiconductor laser device having a refractive index guiding mechanism such as an internal current constriction structure or a ridge structure may be used. A refractive index guided semiconductor laser device will be described below as another embodiment of the present invention.

FIG. 5 shows a shape of a semiconductor laser device according to another embodiment of the present invention in a cross section perpendicular to the waveguide direction. This semiconductor laser device is of a refractive index guiding type having an internal current confinement structure, and a specific method for manufacturing the device will be described below.

On the n-GaAs substrate 21, n-Al_w1Ga_1-w1As composition
Graded layer 22, n-Al_z1Ga_1-z1As lower clad layer 23 (0.57 ≦ z1
≤0.8), n-Al_w2Ga_1-w2As composition graded layer 24, n or i-In
_0.49Ga _0.51P Lower optical waveguide layer 25, In_x1Ga_1-x1As_1-y1P_y1quantum
Well active layer 26 (0≤x1≤0.4, 0≤y1≤0.6, thickness: 3 to 20n
m), p or i-In_0.49Ga_0.51P upper optical waveguide layer 27,
p-Al_w3Ga_1-w3As composition graded layer 28, p-Al_z1Ga_1-z1As top first
Clad layer 29, p-GaAs first etching stop layer 30, p-In
_0.49Ga_0.51P 2nd etching stop layer 31 (thickness: 5 to 20 nm
Degree), n-Al_z3Ga_1-z3As current constriction layer 32 (z1 <z3 ≦ 0.8:
1 μm) and n-GaAs cap layer 33 (10 nm) are sequentially stacked.
To do.

SiO (not shown)₂Form a film, <0
11-4> 1.5-4μ by normal lithography
Striped SiO with a width of about m₂Remove the membrane. next,
This SiO₂N-Ga with sulfuric acid etchant using the film as a mask
As cap layer 33, n-Al_z3Ga_{1-z 3}As current confinement layer 32 is etched
And then p-In with hydrochloric acid based etchant_0.49Ga_{0.5 1}
P by etching the second etching stop layer 31
-Exposing the GaAs first etch stop layer 30. Then S
iO₂Remove the film with a hydrofluoric acid-based etchant and remove p-Al. _z1Ga
_1-z1As upper second cladding layer 35, p-Al_w4Ga_1-w4As composition gradient
A layer 36 and a p-GaAs contact layer 37 are formed.

The p-side electrode 38 is formed, the substrate 21 is polished, and the n-side electrode 39 is formed on the polished surface. After that, one of the cavity surfaces formed by cleaving the sample is coated with a high reflectance and the other is coated with a low reflectance, and thereafter, a semiconductor laser element is formed into chips.

P or i-In _0.49 Ga _0.51 P Upper optical waveguide layer 2
7. The total thickness of the p-Al _w3 Ga _1-w3 As compositionally graded layer 28 and the p-Al _z1 Ga _1-z1 As upper first cladding layer 29 is such that fundamental transverse mode oscillation can be maintained up to high output. That is, the equivalent refractive index step ΔN perpendicular to the stripes of the light emitting portion and parallel to the active layer is set within the range of 2 × 10 ^{−3 to} 7 × 10 ⁻³ .

In the semiconductor laser device having such an internal current constriction structure, since the current passage is formed inside, the contact resistance with the electrode can be reduced and the stripe width can be controlled and the refractive index can be reduced. The wave mechanism can be built in with high precision. Therefore, it is possible to form a highly reliable semiconductor laser device capable of performing fundamental transverse mode oscillation up to high output with good reproducibility.

FIG. 6 shows a shape of a semiconductor laser device according to still another embodiment of the present invention in a cross section perpendicular to the waveguide direction. This semiconductor laser device is of a refractive index waveguide type having a ridge structure, and a specific method for manufacturing this device will be described below.

On the n-GaAs substrate 41, an n-Al _w1 Ga _1-w1 As composition gradient layer 42, an n-Al _z1 Ga _1-z1 As lower cladding layer 43 (0.57 ≦ z1 ≦
0.8), n-Al _w2 Ga _1-w2 As composition gradient layer 44, n or i-In
_0.49 Ga _{0. 51} P lower optical waveguide layer _{45, In x1 Ga 1-x1} As 1-y1 P y1 quantum well active layer 46 (0 ≦ x1 ≦ 0.4,0 ≦ y1 ≦ 0.6, Thickness: 3～20N
m), p or i-In _0.49 Ga _0.51 P upper optical waveguide layer 47,
_{p-Al w3 Ga 1-w3} As graded composition layer _{48, p-Al z1 Ga 1} -z1 As first upper cladding layer _{49, p-In 0.49 Ga 0} .51 P etching stop layer 50
(Thickness: about 5 to 20 nm), p-Al _z1 Ga _1-z1 As upper second cladding layer 51, p-Al _w4 Ga _1-w4 As composition gradient layer 52, and p-GaAs contact layer 53 are formed.

Successively, a contact layer 53, a composition gradient layer 52, and an upper second clad layer are formed by applying a resist and etching by using ordinary lithography and a sulfuric acid type etching solution so as to leave a region of 1.5 to 4 μm in a ridge shape. Remove 51. At this time, the etching automatically stops on the upper surface of the etching stopper layer 50. Subsequently, an insulating film 54 is formed on the laminated surface so as to cover the ridge portion, and the insulating film 54 on the upper surface of the ridge is removed by a normal lithography technique to expose the contact layer 53 and cover the contact layer 53. P
The side electrode 55 is formed, the substrate 41 is polished, and n is applied to the polished surface.
The side electrode 56 is formed. After that, one of the cavity surfaces formed by cleaving the sample is coated with a high reflectance and the other is coated with a low reflectance, and thereafter, a semiconductor laser element is formed into chips.

The p or i-In _0.49 Ga _0.51 P upper optical waveguide layer 47, p-Al _w3 Ga _1-w3 As composition gradient layer 48, p-Al _z1 Ga _1-z1 As
The total thickness of the upper first cladding layer 49 is set so that the fundamental transverse mode oscillation can be maintained up to high output. That is, the equivalent refractive index step ΔN perpendicular to the stripes of the light emitting portion and parallel to the active layer is set within the range of 2 × 10 ^{−3 to} 7 × 10 ⁻³ .

In the above description, the method of manufacturing a semiconductor laser device that oscillates in the fundamental transverse mode as a refraction waveguide type semiconductor laser device having an internal current confinement structure or a ridge structure is described, but a stripe width of 4 μm or more is used. A refractive index guided semiconductor laser device having a multimode oscillation may be used. In a semiconductor laser device having a stripe width of 4 μm or more, the equivalent refractive index step ΔN is 2 × 10 ⁻³ or more. The semiconductor laser device having a wide stripe having such a structure has low noise characteristics and can be used as a high-power semiconductor laser device required for solid-state laser excitation and the like.

The semiconductor laser device structure of the present invention is
Not only the semiconductor laser device with a refractive index guiding mechanism but also a semiconductor laser with a diffraction grating or an optical integrated circuit can be manufactured.

In each of the above embodiments, the GaAs substrate is described as an n-type conductive substrate, but a p-type conductive substrate may be used, and in this case, all of the above-mentioned conductivity is reversed. You can do this.

In the production of each semiconductor laser device, a molecular beam epitaxial growth method using solid or gas as a raw material may be used as a growth method of each semiconductor layer.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to a first embodiment of the present invention, a band gap profile and a refractive index profile.

FIG. 2 is a diagram for explaining a modified example of the semiconductor laser according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view of a modified example of the semiconductor laser device according to the first embodiment of the present invention.

FIG. 4 is a sectional view and band gap profile of a semiconductor laser device according to a second embodiment of the present invention.

FIG. 5 is a sectional view of a semiconductor laser device having an internal current confinement structure according to an embodiment of the present invention.

FIG. 6 is a sectional view of a semiconductor laser device having a ridge structure according to an embodiment of the present invention.

[Explanation of symbols]

1 n-GaAs substrate 2 n-Al _w1 Ga _1-w1 As composition gradient layer 3 n-Al _z1 Ga _1-z1 As lower cladding layer 4 n-Al _w2 Ga _1-w2 As composition gradient layer 5 n or i-In _0.49 Ga _0.51 P lower optical waveguide layer 6 In _x1 Ga _1-x1 As _1-y1 P _y1 quantum well active layer 7 p or i-In _0.49 Ga _0.51 P upper optical waveguide layer 8 p-Al _w3 Ga _1-w3 As composition Graded layer 9 p-Al _z1 Ga _1-z1 As Upper cladding layer 10 p-Al _w4 Ga _1-w4 As Composition graded layer 11 p-GaAs contact layer 12 SiO ₂ film 13 p-side electrode 14 n-side electrode

Claims (9)

[Claims] 1. An AlGaAs lower clad layer on a GaAs substrate,
Lower optical waveguide layer made of InGaAsP or InGaP lattice-matched to GaAs, active layer, InGaAsP or InG lattice-matched to GaAs
A semiconductor laser device comprising an upper optical waveguide layer made of aP, an AlGaAs upper cladding layer, and a GaAs contact layer in this order, wherein the lower and upper optical waveguide layers have a bandgap larger than that of the active layer. Between the lower cladding layer and the lower optical waveguide layer, a band gap having a size between the two band gaps, and a refractive index between the two refractive index or the lower First having a refractive index substantially the same as that of the optical waveguide layer
Of AlGaAs layer, between the upper cladding layer and the upper optical waveguide layer has a bandgap of a size between the two bandgap, and a refractive index of a size between the two. Or a second index having a refractive index substantially the same as that of the upper optical waveguide layer
A semiconductor laser device having the AlGaAs layer of. 2. The band gap of at least a part of the first AlGaAs layer on the lower clad layer side is continuous or steps from the band gap of the lower clad layer to the band gap of the first AlGaAs layer. Change first
Of the second AlGaAs layer, at least a part of the second AlGaAs layer on the side of the upper clad layer has a bandgap from the bandgap of the upper clad layer to the bandgap of the second AlGaAs layer. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is replaced with a second AlGaAs compositionally graded layer that changes continuously or stepwise. 3. A third AlGaAs having a band gap between the GaAs substrate and the lower clad layer which continuously or stepwise changes from the GaAs substrate to the lower clad layer.
A fourth composition comprising a compositionally graded layer, wherein a band gap between the upper clad layer and the GaAs contact layer changes continuously or stepwise from the upper clad layer to the GaAs contact layer.
3. The semiconductor laser device according to claim 1, further comprising an AlGaAs composition gradient layer. 4. The active layer is 0 ≦ x1 ≦ 0.4, 0 ≦ y1 ≦ 0.
_4. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is a quantum well active layer containing In _x1 Ga _1-x1 As _1-y1 P _y1 of 6. 5. The lower and upper optical waveguide layers are made of InGaP, and barrier layers made of InGaAsP having a band gap larger than that of the active layer are provided as upper and lower layers of the active layer. 4. The semiconductor laser device according to any one of 4 above. 6. A refractive index guiding mechanism comprising a current blocking layer provided on the active layer, the current blocking layer having a groove partially formed to serve as a current path to the active layer. The semiconductor laser device according to any one of claims 1 to 5. 7. On the active layer, at least a part from both sides to the end of the passage is removed in a groove shape on both sides of a region serving as a passage of a current to the active layer, and the removed region is formed. 6. The semiconductor laser device according to claim 1, further comprising a refractive index guiding mechanism having a ridge-shaped current path provided therebetween. 8. The width of the electric current passage is 1.5 μm or more and 4 μm or more.
8. The semiconductor laser element according to claim 6, wherein the semiconductor laser element has a refractive index difference of less than m and an equivalent refractive index step difference of 2 × 10 ^{−3 to} 7 × 10 ⁻³ . 9. The semiconductor laser device according to claim 6, wherein the width of the current passage is 4 μm or more, and the equivalent refractive index step is 2 × 10 ⁻³ or more.