JPH0685389A - Semiconductor laser device and manufacturing method thereof - Google Patents

Abstract

(57) [Abstract] [Purpose] Preventing optical absorption near the laser cavity facet by making the energy band gap of the active layer near the cavity facet larger than the energy band gap inside the cavity. To do. Provided is a semiconductor laser device which has a small current spread inside an active layer of a laser device, operates at a low oscillation threshold current, and can oscillate with high efficiency, and a manufacturing method thereof. [Structure] The stress introducing layer 6 is formed above the active layer. The width W1 of the stress introducing layer 6 near the end face of the laser resonator is formed larger than the width W2 of the stress introducing layer 6 near the light emitting portion at the center of the laser resonator. Moreover, the stress introduction layer 6, the second upper cladding layer 14 and the cap layer 8 are formed in a ridge shape. Although the energy band gap of the active layer 3 located below the stress introducing layer 6 becomes narrower, the stress introducing layer 6
Since there is no change in the energy band gap of the active layer 3 which does not exist, carriers can be confined laterally. As a result, the spread of current in the active layer 3 can be reduced, and the efficiency of current injection into the active layer 3 is further improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high power semiconductor laser device used as a light source for an optical disk device, a laser beam printer, etc., and more particularly to a semiconductor laser device having an improved cavity end face structure.

[0002]

2. Description of the Related Art FIG. 8 is a sectional view of a conventional high-power semiconductor laser in which the COD level is improved by utilizing disordering due to impurity diffusion in a superlattice active layer.

This semiconductor laser includes a superlattice active layer 16 composed of an n-type GaAs substrate 1, an n-type AlGaAs lower cladding layer 2 and a GaAs quantum well / AlGaAs barrier layer.
a, p-type AlGaAs upper cladding layer 7, p ⁺ -type GaA
It has an s-cap layer 8, a laser cavity end face vicinity 17 formed into a uniform mixed crystal by Zn diffusion, a p-type electrode 9, and an n-type electrode 10.

The superlattice active layer 16 in the Zn diffused region 17 has an energy bandgap larger than that of the undisordered superlattice active layer 16a region.
It becomes an s mixed crystal layer. In this way, by mixing only the vicinity of the end face of the superlattice active layer 16 to increase the energy band gap, the light absorption loss at this portion is reduced and C
The OD level can be improved. However, in order to fabricate such a semiconductor laser, the fabrication process is complicated such as the fabrication process of a diffusion mask and the diffusion process of Zn into the superlattice, and the optical waveguide is formed near the end face of the laser resonator. There is a problem that there is no.

FIG. 9 shows a schematic view of another conventional high-power semiconductor laser.

To manufacture this semiconductor laser, p-type G
By etching on the aAs substrate 18, a ridge 23 having a narrow width in the vicinity of the end face of the laser resonator and a wide width in the central portion of the laser resonator is formed. N-type GaAs on this ridge 23
The current constriction layer 5 is grown. V-grooves 24 are formed on the wafer thus obtained by etching. This V groove 24
The p-type AlGaAs lower cladding layer 19 and AlGa are formed on the wafer on which the p-type AlGaAs has been formed by the LPE method (liquid phase epitaxial method).
As active layer 20, n-type AlGaAs upper cladding layer 2
1. The n-type GaAs cap layer 22 is sequentially grown. After that, a p-type electrode is formed on the lower surface of the substrate 18 and an n-type electrode is formed on the upper surface of the n-type GaAs cap layer 22.

According to the semiconductor laser having the above structure, the AlGaAs active layer 20 inside the laser resonator is thick due to the anisotropy of crystal growth, and the AlGaAs active layer 20 near the end facet of the laser resonator can be formed thin. The vertical emission angle of the laser light can be narrowed, and even if the vertical emission angle is narrowed, the threshold current hardly increases sharply.

[0008]

[Problems to be Solved by the Invention] However, LPE
Since each layer is grown by the method, it is difficult to reproducibly control the layer thickness of the active layer. Further, there is a problem that there is a coupling loss due to a layer thickness difference between a thick active layer inside the laser resonator and a thin active layer at an end face and a loss due to bending of the active layer.

The present invention is intended to solve the above-mentioned conventional drawbacks, and an object thereof is to spread a current in the active layer little, to operate with a low oscillation threshold current, and to oscillate with high efficiency. A semiconductor laser device and a method for manufacturing the same are provided.

Another object of the present invention is to provide a semiconductor laser device which is relatively easy to manufacture and can realize a semiconductor laser which operates at a high output and a very low threshold value, and a manufacturing method thereof.

[0011]

A semiconductor laser device of the present invention comprises a semiconductor substrate, a lower clad layer, an active layer, a first upper clad layer, which are sequentially laminated on the semiconductor substrate.
A semiconductor laser device having a stress introduction layer, a second upper clad layer, and a cap layer, wherein a width W1 of the stress introduction layer near the end facet of the laser cavity is near the light emitting part at the center of the laser cavity. The width is larger than the width W2 of the stress introducing layer, and the stress introducing layer, the second upper clad layer and the cap layer are formed in a ridge shape, whereby the above object is achieved.

The method of manufacturing a semiconductor laser device according to the present invention comprises:
The step of forming the lower clad layer, the active layer, and the first upper clad layer on the semiconductor substrate, and the width W1 of the stress introducing layer near the end facet of the laser cavity is the stress introducing layer near the light emitting part at the center of the laser cavity. Width W2 of the
The method includes the step of forming the second upper clad layer and the cap layer so as to have a ridge shape, whereby the above object is achieved.

The semiconductor laser device includes a semiconductor substrate, a lower clad layer sequentially laminated on the semiconductor substrate,
The active layer, the first upper clad layer, the n-type current confinement layer, and the stripe shape formed on the n-type current confinement layer and reaching the first upper clad layer in a region other than the vicinity of the end facet of the laser cavity. A groove portion, a stress introduction layer laminated on the n-type current confinement layer and the groove portion, and a second upper clad layer and a cap layer sequentially laminated on the stress introduction layer,
May have.

Further, the method of manufacturing the semiconductor laser device excludes the step of sequentially laminating the lower clad layer, the active layer, the first upper clad layer and the n-type current confinement layer on the semiconductor substrate, and the vicinity of the end facet of the laser resonator. In the region, a step of forming a stripe-shaped groove portion reaching the first upper cladding layer in the n-type current confinement layer, a step of laminating a stress introduction layer on the n-type current confinement layer and the groove portion, and the stress introduction layer A step of sequentially stacking a second upper clad layer and a cap layer on the upper layer may be included.

[0015]

[Function] It has been shown that the partial burying of the InGaAs layer on the GaAs single quantum well layer causes a change in the lateral energy band gap of the GaAs single quantum well layer (reference document Appl. Phys. Lett. 59
(15), p1875-, 1991).

FIG. 1 shows the lateral Eg in a single quantum well layer.
It is a schematic diagram showing (energy band gap).

[0017] Figure 2 shows a width W dependence of the p-type In _Z Ga _1-Z As stress induced layer 6 energy band gap of the single quantum well layer.

By utilizing the above phenomenon, the width of the InGaAs layer is wide near the cavity end face of the semiconductor laser, and the width of the InGaAs layer is narrow inside the cavity so that the active layer is close to the cavity inner side and near the end face. The energy band gap can be differentiated between and.

That is, the energy band gap of the active layer near the end face of the resonator can be made larger than the energy band gap of the active layer inside the resonator.

Further, the InGaAs layer is separated from the active layer in the vicinity of the end face of the resonator of the semiconductor laser, and inside the resonator, I
By making the nGaAs layer close to the active layer, the energy band gap can be made different depending on the position of the active layer. That is, it is possible to make the energy band gap of the active layer near the cavity end face larger than the energy band gap inside the cavity.

Further, according to the present invention, the active layer is formed as a good optical waveguide without forming a step in the active layer or changing the width of the active layer. Further, according to the present invention, it is possible to couple the light reflected on the cavity end face to the active layer again efficiently, as compared with the structure having no optical waveguide in the non-absorption region near the cavity end face.

[0022]

EXAMPLES Reference examples and examples of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto. In the following examples, the molecular beam epitaxial (MBE) method was used to form each layer of the semiconductor laser device of the present invention, but metal organic chemical vapor deposition (MOCV) was used.
The method D) may be used. Also, x, y, and z are each 0
Represents a number greater than 1 and less than 1.

(Reference Example 1) FIG. 3 is a perspective view of a semiconductor laser device, and FIGS. 4a and 4b are cross-sectional views of the semiconductor laser device shown in FIG. 3 taken along broken lines A and B, respectively.

Ga, Al and In, V as group III elements
In the MBE (Molecular Beam Epitaxial) apparatus (not shown) filled with each evaporation source of As as a group element and Si and Be as a dopant, first growth is performed as follows.

[0025] On the n-type GaAs substrate 1, n-type GaAs buffer layer (not shown), n-type Al _x Ga _1-x As lower cladding layer 2, an undoped -Al _y Ga _1-y As single quantum well active Layer 3, p-type Al _x Ga _1-x As upper high-concentration clad layer 4a, p-type Al _x Ga _1-x As upper low-concentration clad layer 4
A wafer is formed by sequentially stacking b and n-type GaAs current confinement layers 5.

This wafer is taken out from the MBE device,
Using a normal photolithography process, a stripe-shaped groove 30 having a constant width and length is formed in a region other than the vicinity of the end facet of the laser cavity to form the n-type GaAs current confinement layer 5 and the p-type Al _x.
It is formed on the wafer by sulfuric acid etching so as to penetrate the Ga _1-x As upper low-concentration clad layer 4b and reach the bottom of the groove 30 to the p-type Al _x Ga _1-x As upper high-concentration clad layer 4a. The width dimension of the portion near the end face of the laser resonator in which the groove 30 is not formed is typically 20 to 50 μm.
The width of the stripe-shaped groove 30 is preferably 500 angstroms to 3 μm, and the depth is 1 to 3 μm.
1.5 μm is preferred.

Next, the wafer having the groove 30 formed therein is reintroduced into the MBE apparatus, and the second growth is performed as follows.

The substrate temperature is low, and the p-type In _z Ga _1-z As stress introducing layer 6 and the p-type Al _x Ga are formed on the stripe-shaped groove.
_{The 1-x} As clad layer 7 and the p ⁺ type GaAs cap layer 8 are sequentially laminated.

Then, a p-type electrode 9 and an n-type electrode 10 are formed on the upper surface of the p ⁺ -type GaAs cap layer 8 and the lower surface of the substrate 1, respectively, through a normal semiconductor laser element process to obtain a semiconductor laser element.

In the vicinity of the cavity end face of the obtained laser device (FIG. 4b), the stress introducing layer 6 is located away from the active layer 3, and therefore the active layer 3 is not affected by the stress introducing layer 6 and is active. The energy bandgap (Eg) of the layer 3 is Eg of the original material, and the current blocking layer 5 blocks the current.

On the other hand, inside the laser resonator (FIG. 4A), the stress introducing layer 6 is close to the active layer 3 and the active layer 3 is affected by the stress introducing layer 6, so that the Eg of the active layer 3 is narrow. Has become.

That is, by making the energy bandgap of the active layer 3 near the cavity facet larger than the energy bandgap inside the cavity, an optical waveguide structure is formed in the non-absorption region near the cavity facet.

Further, the current injected into the region 11 of the non-doped Al _y Ga _1-y As single quantum well active layer 3 where the energy band gap is narrowed is efficiently confined, and the active layer 3 within the active layer 3 is confined. It is possible to reduce the spreading current. Further, the laser light is efficiently confined in the area 11. Furthermore, the bottom of the stripe-shaped groove portion 30 is p-type Al _x Ga _{1 -x} A.
Since it is formed in the upper high-concentration clad layer 4a,
The current spread in the p-type Al _x Ga _1-x As upper cladding layer 4b can be reduced, and a semiconductor laser that operates at a very low threshold with a high output can be realized.

The n-type GaAs current confinement layer 5 is an n-type A
Of course, it may be an lGaAs layer. Furthermore, in the above example, the p-type In _z Ga _1-z As stress induced layer 6 in the vicinity of the non-doped -Al _y Ga _1-y As single quantum well active layer 3 is present, the p-type In _z Since the Ga _1-z As stress introduction layer 6 is set to be very thin (for example, 10 to 60 angstrom), it has no effect on the light emitted from the active layer 3 and has no particular effect. As the stress introduction layer 6,
Other than the above, InGaAsP type may be used.

Reference Example 2 Another reference example is shown in FIGS. 5a and 5b. 5a and 5b are cross-sectional views showing the vicinity of the end face of the laser resonator and the inside of the laser resonator, respectively.

Ga, Al and In as group III elements,
In the MBE (Molecular Beam Epitaxial) apparatus (not shown) filled with As sources as group V elements and Si and Be evaporation sources as dopants, first growth is first performed as follows.

[0037] n-type GaAs buffer layer on the n-type GaAs substrate 1 (not shown), n-type Al _x Ga _1-x As lower cladding layer 2, an undoped -Al _y Ga _1-y As single quantum well active layer 3, p-type Al _x Ga _1-x As upper cladding layer 7, p-type GaAs etch stop layer 13, n-type Al _x Ga _1-x As
The current confinement layer 5a and the n-type GaAs current confinement layer 5 are sequentially laminated to form a wafer.

This wafer was taken out from the MBE device,
By a normal photolithography process, a stripe-shaped groove portion 30 having a constant width and length is formed in a region other than the vicinity of the end facet of the laser cavity by selective etching to form an n-type GaAs.
The current confinement layer 5 and the n-type Al _x Ga _{1 -x} As current confinement layer 5 a are penetrated and etched so as to stop on the p-type GaAs etch stop layer 13.

Next, the wafer on which the groove 30 is formed is MB
It is reintroduced into the E apparatus and the second growth is performed as follows.

With the substrate temperature kept relatively low, the p-type In _z Ga _{1 -z} As stress introducing layer 6 is formed on the stripe-shaped groove portion 30,
p-type Al _x Ga _1-x As second upper cladding layer 14, p ⁺
The type GaAs cap layer 8 is sequentially laminated.

Then, a p-type electrode 9 and an n-type electrode 10 are formed on the upper surface of the p ⁺ type GaAs cap layer 8 and the lower surface of the substrate 1, respectively, through a normal semiconductor laser element process to obtain a semiconductor laser element.

In the vicinity of the cavity end face of the obtained laser device (FIG. 5a), the stress introducing layer 6 is located away from the active layer 3, and the energy band gap of the active layer 3 is not affected by the stress introducing layer 6. (Eg) is E of the original material
g, and the current is blocked by the current constriction layer 5.

On the other hand, inside the laser resonator (FIG. 5b), the stress introducing layer 6 is close to the active layer 3 and the Eg of the active layer 3 is increased.
Is narrowing.

That is, by making the energy band gap of the active layer near the cavity end face larger than the energy band gap inside the cavity, an optical waveguide structure in the non-absorption region near the cavity end face is formed.

Further, the p-type AlGaAs upper cladding layer 7 is set to be very thin (for example, 200 to 200).
0 angstroms), spreading of the injected current, where most negligible, further undoped -Al _y G
a _1-y As single quantum well The current injected into the region 11 in which the energy band gap of the active layer 3 is narrowed is efficiently confined, and the spreading current in the active layer can be reduced. Since the structure is such that no current flows in the vicinity of the cavity facets, a semiconductor laser that operates at a very low threshold with a high output can be realized.

[0046] Further, the non-doped -Al _y Ga _1-y As the p-type In _z Ga _1-z As stress induced layer 6 in the vicinity of the single quantum well active layer 3 is present, the p-type an In _z Ga _{The 1-z} As stress introduction layer 6 is set to be very thin (for example,
10 to 60 angstroms), the light emitted from the active layer has no absorption effect and has no particular effect. Further, the p-type GaAs etch stop layer 13 in the vicinity of the non-doped -Al _y Ga _1-y As single quantum well active layer 3 is present, the p-type GaAs etch stop 13 is set very thin Therefore (for example, 100 to 200 angstrom), the light emitted from the active layer has no absorption effect and has no particular effect.

(Embodiment 1) Embodiments of the present invention are shown in FIGS.
A will be described with reference to FIG.

FIG. 6 is a plan view of the semiconductor laser device, and FIG.
6A and 6B respectively show the semiconductor laser device of FIG.
It is sectional drawing cut | disconnected by A'and BB '.

Using the MBE method, an n-type GaAs buffer layer (not shown) and n-type Al _x G are formed on the n-type GaAs substrate 1.
a _1-x As lower cladding layer 2, an undoped -Al _y Ga
_1-y As single quantum well active layer 3, p-type Al _x Ga _1-x As
The upper clad layer 7, the p-type In _z Ga _1-z As stress introducing layer 6, the p-type Al _x Ga _1-x As upper clad layer 14, and the p ⁺ -type GaAs cap layer 8 are sequentially laminated to form a wafer.

This wafer is taken out from the MBE device,
P-type Al _x Ga is formed by a normal photolithography process.
_1-x As etching up to the upper clad layer 7, width W1 near the end face of the laser cavity, width W at the center of the laser cavity
The stripe-shaped ridge 31 having 2 is a p-type In _z Ga _{1 -z}
The As stress introducing layer 6, the p-type Al _x Ga _{1 -x} As second upper cladding layer 14 and the p-type GaAs cap layer 8 are formed.

Next, an insulator layer 15 is vapor-deposited on this wafer, and etching for a current path is performed only in the central portion of the laser resonator by a normal photolithography process.

P-type In _z near the end face of the laser cavity
Ga _1-z As the width W1 of the stress introduction layer 6, p-type in the laser resonator central portion In _z Ga _1-z As the width W of the stress introduction layer 6
The energy bandgap of the active layer is wider near the end facet of the laser cavity and narrower at the center of the laser cavity because it is formed larger than that of FIG. 2 (FIGS. 6a and 6b). Can be prevented from being absorbed.

Further, since the current does not flow in the vicinity of the end face of the laser resonator, the temperature rise of the end face can be suppressed and the deterioration occurring on the end face can be prevented, so that high output operation is possible and reliable. It is possible to realize a semiconductor laser that operates with a very high threshold and a very low threshold.

Further, the p-type In _z Ga _1-z As stress introducing layer 6 exists near the non-doped-Al _y Ga _1-y As single quantum well active layer 3, and this p-type In _z Ga is present. _{The 1-z} As stress introduction layer 6 is set to be very thin (for example,
10 to 60 angstroms), the light emitted from the active layer has no absorption effect and has no particular effect.

As the stress introducing layer 6, other than the above, InG
It may be an aAsP system.

Needless to say, a semiconductor laser can be manufactured within the scope of the claims using materials other than those used in the above example.

[0057]

As described above, according to the present invention,
Since the energy bandgap in the active layer near the end facet of the laser cavity is larger than the energy bandgap in the central part of the laser cavity, it is possible to prevent optical absorption of laser light near the end facet of the laser cavity. . Further, since the structure is such that no current flows near the end face of the laser resonator, the temperature rise of the end face can be suppressed and the deterioration occurring on the end face can be prevented, so that high output operation is possible and the reliability is high. It is possible to realize a semiconductor laser that operates at a high output and an extremely low threshold.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an energy band gap in a lateral direction of an active layer.

FIG. 2 p-type In of the energy band gap of the active layer
It is a figure which shows the width dependence of a GaAs layer.

FIG. 3 is a perspective view of a semiconductor laser device of a reference example of the present invention.

4a and 4b are cross-sectional views of the semiconductor laser device of FIG. 3 taken along the broken lines A and B, respectively.

5A and 5B are cross-sectional views of a semiconductor laser device according to another reference example of the present invention.

FIG. 6 is a plan view of a semiconductor laser device according to an embodiment of the present invention.

7a and 7b are cross-sectional views of the semiconductor laser device of FIG. 6 taken along the broken lines AA 'and BB', respectively.

FIG. 8 is a sectional view of a conventional semiconductor laser.

FIG. 9 is a schematic view of a conventional semiconductor laser.

[Explanation of symbols]

1 n-type GaAs substrate 2 n-type Al _x Ga _1-x As lower cladding layer 3 doped -Al _y Ga _1-y As single quantum well active layer 4a p-type Al _x Ga _1-x As upper high concentration clad layer 4b p-type Al _x Ga _1-x As upper low-concentration clad layer 5 n-type GaAs current confinement layer 5a n-type Al _x Ga _1-x As current confinement layer 6 p-type In _z Ga _1-z As stress introduction layer 7 p-type Al _x Ga _1-x As upper cladding layer 8 p-type GaAs cap layer 9 p-type electrode 10 n-type electrode 11 region where the energy band gap is narrowed 12 energy band gap is the original region 13 p-type GaAs etch stop layer 14 p-type AlGaAs second clad layer 15 insulator layer 16 GaAs quantum well / AlGaAs barrier layer superlattice active layer 17 Zn Rays formed into a uniform mixed crystal by diffusion Resonator facet vicinity 18 p-type GaAs substrate 19 p-type AlGaAs lower cladding layer 20 AlGaAs active layer 21 n-type AlGaAs upper cladding layer 22 n-type GaAs cap layer 30 groove 31 Ridge

Claims (2)

[Claims] 1. A semiconductor substrate, and a lower clad layer, an active layer, a first upper clad layer, a stress introducing layer, a second upper clad layer, and a cap layer, which are sequentially laminated on the semiconductor substrate. In the semiconductor laser device having, the width W1 of the stress introducing layer near the end face of the laser resonator is formed larger than the width W2 of the stress introducing layer near the light emitting portion at the center of the laser resonator, and the stress introducing layer, A semiconductor laser device in which the second upper cladding layer and the cap layer are formed in a ridge shape. 2. A step of forming a lower clad layer, an active layer, and a first upper clad layer on a semiconductor substrate, and a width W1 of the stress introducing layer near the end facet of the laser cavity are such that a light emitting portion at the center of the laser cavity. A method of manufacturing a semiconductor laser device, comprising the step of forming the stress introduction layer, the second upper clad layer and the cap layer so as to have a ridge shape, the width being larger than a width W2 of the stress introduction layer in the vicinity thereof.