JPH04296081A - Visible beam semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a visible beam semiconductor laser which is easily manufactured, enhanced in yield, lessened in threshold value, and able to emit laser beams nearly circular in cross section. CONSTITUTION:A second conductivity type GaAs diffusion stopper layer 6, a second conductivity type AlGaInP sub-clad layer 7, and a second conductivity type GaAs contact layer 8 are successively laminated on an AlGaInP double hetero-structure, and impurities of first conductivity type are diffused into the GaAs contact layer 8 from its front side. An impurity diffusion region 9 is provided inside the GaAs contact layer 8 so as to enable a non-diffusion region inside the sub-clad layer 7 to be smaller than that inside the GaAs contact layer 8 in width taking advantage of the diffusion rate difference of impurity between GaAs and AlGaInP.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a visible light semiconductor laser, and more particularly to a visible light semiconductor laser that can be easily manufactured with good reproducibility, has a low threshold value, and can emit a nearly circular laser beam.

0002

[Prior Art] FIGS. 4(a) to 4(d) show, for example, "In
GaAlP transverse stabilized
“Visible Laser Diode Fabricated by MOCVD Selective Growth” (“InGaAlP Transverse Sta.
bilized Visible Laser Diod
es Fabricated by MOCVD Se
Lective Growth “M. Ishika
wa et, al. , Extended Abst
racts of the 18th conference
nce on SSDM, 1986, pp153-
156) are cross-sectional views showing each step of the conventional method for manufacturing a visible light semiconductor laser disclosed in Japanese Patent No. 156). In the figure, 41 is an n-type (hereinafter referred to as n-) GaAs substrate, 42 is an n-AlGaInP lower cladding layer, and 43 is an undoped G
aInP active layer, 44 is p-type (hereinafter referred to as p-) AlG
aInP upper cladding layer, 45 p-GaInP band discontinuous relaxation layer, 46 SiNx film, 47 n-GaAs
The current blocking layer 48 is a p-GaAs contact layer.

Next, the manufacturing process will be explained. Figure 4 (a
), first, n-type (hereinafter referred to as n-) GaA
n-AlGaInP lower cladding layer 42 on s-substrate 41,
Undoped GaInP layer 43, p type (hereinafter referred to as p-)
An AlGaInP upper cladding layer 44 and a p-GaInP band discontinuous relaxation layer 45 are sequentially laminated by MOCVD.

Next, as shown in FIG. 4(b), a SiNx film 46 is formed on the surface of the p-GaInP band discontinuous relaxation layer 45 using the plasma CVD method, and then a SiNx film 46 is formed using a normal photolithography technique. A photoresist is patterned, and using this resist as a mask, the above Si is etched using a hydrofluoric acid (hereinafter referred to as HF) or hydrochloric acid etching solution.
Nx film 46, p-GaInP band discontinuous relaxation layer 45
is selectively removed, and the p-AlGaInP upper cladding layer 44 is subsequently etched using a hot H2 SO4 etchant. In this case, the p-AlGaInP upper cladding layer 44 is not etched until it reaches the GaInP active layer 43, and p-AlGaInP with a desired thickness t is etched on both sides.
Stop leaving the P upper cladding layer.

Next, as shown in FIG. 4(c), the MOC
The n-GaAs current blocking layer 47 is formed using the VD method as shown in FIG.
It grows selectively on the portions removed in the etching step (b).

Next, as shown in FIG. 4(d), SiN
After removing the x film 46 using an HF-based etching solution, the p-GaAs contact layer 48 is removed using the MOCVD method again.
form. Then, the p-side electrode 4 is placed on the contact layer 48.
9, an n-side electrode 50 is formed on the back surface of the substrate 41 to complete the device.

[0007]

[Problems to be Solved by the Invention] Since the conventional visible light semiconductor laser is constructed as described above, FIG.
The three crystal growth steps shown in (c) and (d) are required, making the laser manufacturing process complicated, and the thickness t of the p-AlGaInP on both sides of the ridge structure needs to be controlled by etching. There were problems in that the thickness t varied within the wafer, poor reproducibility, and yield decreased. Furthermore, due to limitations in photolithography and etching technology, the ridge width w can only be narrowed to about 2 microns, so the light emitting region width becomes wider than 5 microns, making it difficult to lower the threshold current. Furthermore, there were other problems in that the shape of the laser beam emitted from the end facet was an ellipse that was elongated in the width direction of the active region.

[0008] This invention was made to solve the above-mentioned problems, and the manufacturing process is easy and the yield can be improved, and a laser beam having a shape close to a circle can be emitted with a low threshold value. The purpose is to obtain a visible light semiconductor laser.

[0009]

[Means for Solving the Problems] A visible light semiconductor laser according to the present invention includes a GaAs substrate of a first conductivity type, at least an AlGaInP lower cladding layer of a first conductivity type, an undoped GaInP active layer, and a GaInP active layer of a second conductivity type. It has a structure in which an AlGaInP upper cladding layer, a GaAs diffusion stopper layer of a second conductivity type, an AlGaInP sub-cladding layer of a second conductivity type, and a GaAs contact layer of a second conductivity type are sequentially laminated, and from the surface of the GaAs contact layer. The above GaA
An impurity diffusion region is formed by diffusing an impurity of the first conductivity type so as to leave a striped non-diffusion region in the center of each layer until reaching the s-diffusion stopper layer.

Further, in the visible light semiconductor laser according to the present invention, the sub-cladding layer has a natural superlattice structure, and the natural superlattice structure in the diffused region is disordered by diffusion of the impurity.

[0011]

[Operation] The visible light semiconductor laser in this invention has the first
At least a first conductivity type A is formed on a conductivity type GaAs substrate.
lGaInP lower cladding layer, undoped GaInP active layer, second conductivity type AlGaInP upper cladding layer, second conductivity type GaAs diffusion stopper layer, second conductivity type AlGa
It has a structure in which an InP sub-cladding layer and a GaAs contact layer of the second conductivity type are sequentially laminated, and the GaAs
This is because the structure includes an impurity diffusion region formed by diffusing an impurity of the first conductivity type so as to leave a striped non-diffusion region in the center of each layer from the surface of the contact layer to the GaAs diffusion stopper layer. Since it can be manufactured by one step of crystal growth and impurity diffusion, the manufacturing process is extremely easy and the yield can be improved. Also, compared to the GaAs contact layer, the AlGaIn
Since the diffusion rate of impurities in the P sub-cladding layer is high, the width of the non-diffusion region in the sub-cladding layer is formed narrower than the width of the non-diffusion region in the GaAs contact layer, and the current confinement is sufficiently narrowed. It is possible to emit a laser beam with a shape close to a circle at the threshold value.

Furthermore, in the present invention, the sub-cladding layer is formed under conditions where a natural superlattice structure is formed, and the natural superlattice structure of the diffusion region is disordered by the diffusion of the impurity. Since a refractive index difference can be formed in the lateral direction within the AlGaInP sub-cladding layer, an effective refractive index difference is formed in the lateral direction of the active layer, making it possible to oscillate in a single transverse mode.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the structure of a visible light semiconductor laser according to an embodiment of the present invention. In the figure, 1 is a p-GaAs substrate with a thickness of about 100 microns;
On top, a p-GaInP band discontinuous relaxation layer 2 with a thickness of about 0.1 micron, and a p-AlGaI layer 2 with a thickness of about 1.0 micron.
nP lower cladding layer 3, undoped GaInP active layer 4 with a thickness of about 0.1 micron, n-A with a thickness of about 0.3 micron
an lGaInP upper cladding layer 5, an n-GaAs diffusion stopper layer 6 with a thickness of approximately 0.02 microns, an n-AlGaInP sub-cladding layer 7 with a natural superlattice structure of approximately 0.7 microns in thickness, and a thickness of approximately 3.0 microns. Micron n-GaAs contact layers 8 are sequentially stacked. Further, 9 is a Zn diffusion region, 10 is an n-side electrode, and 11 is a p-side electrode.

Next, the manufacturing process of the visible light semiconductor laser according to this embodiment will be explained. FIG. 2 is a diagram showing the manufacturing process of the visible light semiconductor laser in FIG.
The same reference numerals are the same or equivalent parts, and 12 is SiNx
The film 13 is a SiO2:ZnO mixed film.

First, as shown in FIG. 2(a), the MOC
Using the VD method, p-GaIn is deposited on the p-GaAs substrate 1.
P-band discontinuous relaxation layer 2, p-AlGaInP lower cladding layer 3, undoped GaInP active layer 4, n-AlGa
InP upper cladding layer 5, n-GaAs diffusion stopper layer 6
, n-AlGaInP sub-cladding layer 7, n-GaAs
Contact layers 8 are formed by sequentially stacking them. By appropriately setting growth conditions such as growth temperature and V/III ratio, the sub-cladding layer 7 can have a natural superlattice structure. In this example, the growth temperature is 650°C.

Next, as shown in FIG. 2(b), n-
A SiNx layer 12 is formed on the GaAs contact layer 8,
A predetermined width (~10
A stripe of SiNx layer 12 of .mu.m) is formed. Furthermore, as shown in FIG. 2(c), a SiO2:ZnO mixed film 13, which will serve as a Zn diffusion source, is formed by sputtering on the stripes of the n-GaAs contact layer 8 and the SiNx layer 12. time, perform solid-phase diffusion, and Z
n is diffused until reaching the n-GaAs diffusion stopper layer 6 to obtain a desired width w between the Zn diffusion regions.

In the conventional example, the shape of the ridge is trapezoidal, and even if it is about 2 microns at the top, it is much wider at the bottom, and in reality, the width of the active region is about 7 microns, making it difficult to Although it was difficult to realize a threshold value or a circular laser beam, by the diffusion of this example, the width w between the Zn diffusion regions can be controlled to be almost constant in the layer thickness direction.
Since the spread of the current is small, by setting the width w to about 2 microns, it is possible to realize a low threshold value and a laser beam having a shape close to a circle.

Finally, as shown in FIG. 2(d), Si
The Nx layer stripe is removed, an n-side electrode 10 is formed on the n-GaAs contact layer 8, and a p-side electrode 11 is formed on the back surface of the p-GaAs substrate 1, thereby completing a visible light semiconductor laser.

Next, the operation will be explained. Zn mentioned above
In the diffusion process, the n-GaAs contact layer 8, n-AlGaInP sub-cladding layer 7, n-
-The Zn diffusion region of the GaAs diffusion stopper layer 6 has a p-type conductivity type and functions as a current confinement layer. At this time, as shown in FIG. 3, compared to the GaAs contact layer 8 and the GaAs diffusion stopper layer 6, the AlGaInP sub-cladding layer 7
Since the diffusion rate of Zn is several tens of times higher, n
-n-AlGaIn compared to GaAs contact layer 8
In the P sub-cladding layer 6, the distance between the current confinement layers becomes narrower. Therefore, the diffusion mask width can be made wide (up to 10 μm), and current confinement can be sufficiently performed.

In addition, the Zn diffusion region of the n-AlGaInP sub-cladding layer 7 has a disordered AlGaInP natural superlattice structure, so that the cross-sectional refractive index distribution in the n-AlGaInP sub-cladding layer 7 and the Zn diffusion region 9 is n. - The refractive index of the AlGaInP sub-cladding layer 7 becomes larger than the refractive index of the Zn diffusion regions 9 on both sides. As a result, if the thickness d of the n-AlGaInP cladding layer 5 is small (~0.3 μm or less), the light emitted from the undoped GaInP active layer 4 is diffused by the Zn of the n-AlGaInP sub-cladding layer 7, which has a large refractive index. Since it is effectively confined in the vicinity of the undoped GaInP active layer 4, an effective refractive index difference is formed in the lateral direction of the undoped GaInP active layer 4, and single transverse mode oscillation is possible.

Next, the operation will be explained. When a forward bias is applied to the pn junction, the current flows through the Zn diffusion layer 9
It is constricted and implanted into the undoped GaInP active layer 4. These injected carriers are confined within the active layer by the heterojunction, recombine, and emit light. Here, since the effective refractive index distribution is formed in the horizontal direction of the active layer as described above, the light is concentrated in the portions having a high refractive index and is guided in the vertical direction in a stripe shape. The guided light reaches laser oscillation in a Fabry-Perot type resonator formed by opposing cleavage end faces perpendicular to the depth direction of the stripe. Here, as described above, since the width of the striped impurity non-diffusion region in the sub-cladding layer 7 can be formed sufficiently narrow, it is possible to obtain a laser beam with a low threshold and a nearly circular shape.

Note that in the above embodiment, the sub-cladding layer 7
has a natural superlattice structure, but even if the subcladding layer does not have a natural superlattice structure, a current confinement structure is achieved by impurity diffusion, so lateral confinement of light is achieved by the current intensity distribution in the active layer. It is possible.

Further, in the above embodiment, solid phase diffusion was used as a method for forming the Zn diffusion region, but vapor phase diffusion may also be used, and in some cases, n-A may be formed by thermal drive.
It is also possible to further narrow the stripe width by promoting Zn diffusion in the lateral direction of the lGaInP sub-cladding layer.

[0024]

As described above, in the visible light semiconductor laser according to the present invention, at least the AlGaInP lower cladding layer of the first conductivity type, the undoped GaInP active layer, and the second conductivity type are formed on the GaAs substrate of the first conductivity type. shape of AlGa
It has a structure in which an InP upper cladding layer, a GaAs diffusion stopper layer of a second conductivity type, an AlGaInP sub-cladding layer of a second conductivity type, and a GaAs contact layer of a second conductivity type are sequentially laminated, and from the surface of the GaAs contact layer. Since the structure includes an impurity diffusion region formed by diffusing impurities of the first conductivity type so as to leave a striped non-diffusion region in the center of each layer until reaching the GaAs diffusion stopper layer, one crystallization Since it can be manufactured through the steps of growth and impurity diffusion, the manufacturing process is extremely easy and the yield can be improved. Also, GaAs
Since the diffusion rate of impurities in the AlGaInP sub-cladding layer is higher than that in the contact layer, the width of the non-diffusion region in the sub-cladding layer is formed narrower than the width of the non-diffusion region in the GaAs contact layer. This has the effect of realizing a semiconductor laser that can emit laser light in a shape close to a circle with a low threshold due to sufficient current confinement.

Further, according to the present invention, the sub-cladding layer is formed under conditions where a natural superlattice structure is formed, and the natural superlattice structure of the diffusion region is disordered by diffusion of the impurity. Since a refractive index difference can be formed in the lateral direction within the AlGaInP sub-cladding layer, an effective refractive index difference is formed in the lateral direction of the active layer, which has the effect of enabling single transverse mode oscillation.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the structure of a visible light semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the manufacturing process of the visible light semiconductor laser shown in FIG. 1;

FIG. 3 is a diagram showing the diffusion rate of Zn in GaAs and AlGaInP.

FIG. 4 is a cross-sectional view showing the manufacturing process of a conventional visible light semiconductor laser.

[Explanation of symbols]

1 p-GaAs substrate 2 p-GaInP band discontinuous relaxation layer 3
p-AlGaInP lower cladding layer 4 undoped GaInP active layer 5 n-AlGaInP upper cladding layer 6 n-GaAs diffusion stopper layer 7
n-AlGaInP sub-cladding layer 8 n-
GaAs contact layer 9 Zn diffusion region 10 n-side electrode 11 p-side electrode

Claims (2)

[Claims] [Claim 1] A first conductivity type GaAs substrate is provided with a first conductivity type GaAs substrate.
Conductive type AlGaInP lower cladding layer, undoped Ga
InP active layer, second conductivity type AlGaInP upper cladding layer, second conductivity type GaAs diffusion stopper layer, second conductivity type AlGaInP sub-cladding layer, and second conductivity type G
A laminated structure in which aAs contact layers are sequentially arranged, and an impurity of a first conductivity type is diffused so as to leave a non-diffused region in a stripe shape at the center of each layer from the surface of the GaAs contact layer to the GaAs diffusion stopper layer. an impurity diffusion region formed in GaAs and AlGaIn.
A visible light semiconductor characterized in that the width of the non-diffused region in the sub-cladding layer is narrower than the width of the non-diffused region in the GaAs contact layer due to the difference in diffusion rate of impurities in P. laser. 2. The sub-cladding layer is formed under conditions that form a natural superlattice structure, and the region where the impurity is diffused has a disordered natural superlattice structure. 1. The visible light semiconductor laser according to 1.