JPH0666525B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is directed to AlG having an emission wavelength in the visible light band (600 nm band).
aInP-based semiconductor laser

(Prior Art) AlGaInP-based visible light semiconductor lasers have been actively researched for several years and are about to be put to practical use soon. AlGa
One of the largest uses of InP semiconductor lasers is optical discs. To use it as an optical disc head,
It is necessary to reduce the astigmatism of the semiconductor laser itself. As a method of reducing this astigmatism, it is known from research on AlGaAs semiconductor lasers that the method of transverse mode control may be changed from gain (or loss) waveguide type to refractive index waveguide type. , At present, there is no report of the index guided laser in the AlGaInP semiconductor laser.
Therefore, here, as the prior art, an AlGaInP-based index-guided laser that can be inferred from the lateral mode control structure of an AlGaAs-based semiconductor laser, and the invention of the present inventor are disclosed.
-189839 AlGaInP-based index-guided laser.

First, FIGS. 3 and 4 show an AlGaInP-based index-guided laser, which is inferred from an AlGaAs-based transverse mode control laser. FIG. 3 shows a self-aligned laser which is usually produced by metalorganic pyrolysis vapor phase epitaxy (hereinafter abbreviated as MOVPE method). After removing the current block layer 4 only in the central current injection portion, the entire surface is shown. Is a laser in which a clad layer 3'is laminated on the above to form a current injection path. FIG. 4 shows, contrary to FIG. 3, after partially thinning the cladding layer 3 other than the current injection portion,
The laser has a structure in which the current block layer 4 is embedded. Third
In FIG. 4 and FIG. 4, the current block layer 4 has an Al composition larger than that of the AlGaInP clad layer forming the current injection portion.
lGaInP or AlInP is used, and the actual refractive index difference is provided between the current injection part and the non-excitation region (current block layer part). Further, in the structure shown in FIG. 4, room-temperature continuous-wave oscillation has been reported in a loss-guiding laser in which the block layer 4 is GaAs [Reference: Extended Abstracts of the 18th Confere
nce on Solid State Devices and Materials, Tok
yo, 1986, pp.153-156]. However, the lasers having the structures shown in FIGS. 3 and 4 have problems in structure or fabrication as described below.

First, regarding the laser shown in FIG. 3, the biggest problem with this structure is that the cladding layer 3 and the cladding layer 3'at the current injection portion.
This is a problem at the regrowth interface. That is, when the laser shown in FIG. 3 is produced, the cladding layer 3 having a high Al composition is exposed to the atmosphere and is oxidized, so that the cladding layer 3'laminated thereabove is not laminated properly and the crystal quality is deteriorated. Alternatively, increasing the resistance of the regrowth interface becomes a problem. Further, this regrowth interface is located in the immediate vicinity of the active layer 1 and has a high optical density during laser oscillation, so many defects introduced into the regrowth interface significantly deteriorate the reliability of this laser. Also,
For the laser shown in FIG. 4, AlGa is the current blocking layer 4.
There are the following problems when re-growing InP or AlInP. That is, in FIG. 4, when AlGaInP or AlInP to be the current blocking layer 4 is stacked by selective epitaxial growth by the MOVPE method, precipitation of polycrystalline lumps on the dielectric film to be the selective mask is accompanied by an increase in the Al composition of AlGaInP. Since it increases rapidly, selective embedding becomes very difficult.

Next, as a structure for solving the problems of the lasers of FIGS. 3 and 4, the laser of Japanese Patent Application No. 62-189839 previously invented by the inventor of the present application and filed by the same applicant as the present application is the fifth one. Shown in the figure. First, the structure of FIG. 5 will be described. GaAs (100)
A mesa in the (011) direction is formed on the substrate 6, and then a buffer layer 7 made of GaAs is laminated on the mesa. At this time,
Due to the plane orientation dependence of the growth rate, Ga deposited on the mesa
It is known that the side surface of As retains the (111) B plane, and eventually the growth on the mesa ends with a triangular shape [Reference: S61 Autumn Proceedings of the Japan Society of Applied Physics 27P-T- 14, p
p.160]. Next, on the GaAs mesa having the (111) B surface on its side surface, the cladding layer 2 made of AlGaInP or AlInP, GaIn
Active layer made of P 1, clad layer made of AlGaInP or AlInP
3, the current block layer 4 made of GaAs of the same conductivity type as the substrate,
MOVPE growth is performed sequentially to form a double heterostructure. At this time, focusing on the stacking on the side surface of the mesa, the clad layers 2, 3
AlGaInP or AlInP, which becomes, is the (111) B plane mesa side surface and the (100) plane mesa top surface and mesa bottom surface.
Grow at an equivalent growth rate. This is very different from the state of stacking of AlGaAs series. In the case of the AlGaAs system, the growth on the side surface starts only after the mesa side surface is deviated to some extent from the (111) B surface due to the crawl from the bottom surface. On the other hand, in GaInP that becomes the active layer 1, (111)
The growth rate on the B side is extremely slow compared to the growth rate on the (100) side. Therefore, by first laminating the buffer layer 7 made of GaAs, a new mesa structure having a (111) B plane on the side surface is formed, and then by laminating a double hetero structure having GaInP as an active layer, the mesa structure is formed. At the top, GaIn
A semiconductor laser having a buried hetero (BH) structure in which the P active layer 1 is buried with AlGaInP or AlInP cladding layers 2 and 3 is formed. Then, finally, the current injection path is formed by utilizing the inversion of the conductivity type by Zn diffusion. The laser of FIG.
Oxidation of a high Al composition layer, which was a problem in the lasers shown in FIGS. 3 and 4, in a refractive index guided semiconductor laser manufactured by skillfully utilizing the plane orientation dependence in MOVPE growth of AlGaInP-based material. , Problems such as stacking faults have been improved.

(Problems to be Solved by the Invention) However, on the other hand, the structure of FIG. 5 has the following problems as a current injection mechanism.

First, as a first point, the structure of FIG. 5 uses the inversion of the conductivity type by a complicated Zn diffusion process as a current injection mechanism, so that a mask shift is likely to occur in the window process for Zn diffusion, There is concern that the kink level may decrease due to higher-order mode excitation, the threshold current may increase, and eventually the yield may decrease and the reliability may deteriorate. In addition, as a second point, in the structure of FIG. 5, a high temperature treatment called a Zn diffusion step is performed after the double hetero structure is formed.
The deterioration of the crystal quality of the active layer becomes a problem.

Therefore, an object of the present invention is to solve the above problems, and to provide a high-quality AlGaInP-based index-guided semiconductor laser that is easy to manufacture, has high reproducibility, and is highly reliable.

(Means for Solving the Problems) The means provided by the present invention for solving the above-mentioned problems is that Ga on a GaAs (100) substrate having a (011) direction mesa.
GaAs having a buffer layer made of As and laminated on the mesa
The side surface of the buffer layer is a (111) B surface, and is a clad layer that is connected and laminated to the upper surface of the mesa and the lower surface of the mesa. The clad layer sandwiches the active layer that is separated into the upper surface of the mesa and the lower surface of the mesa. A multi-layer heterostructure including a double heterostructure formed by imprinting is formed on the buffer layer, the clad layer has a larger band gap than the active layer, and the clad layer is made of AlGa
InP or AlInP, the active layer is a semiconductor laser comprising a GaInP layer formed by NOVPE method, between the substrate and the buffer layer, GaAs that covers only the mesa side surface and the mesa bottom surface of the substrate. And a current blocking layer, the current blocking layer being a layer formed in a self-aligned manner by a selective epitaxial growth method.

(Operation) While the laser of FIG. 5 has a structure in which a current injection path is formed by Zn diffusion after the formation of the double hetero structure, the laser of the present invention forms the current blocking layer before forming the double hetero structure. In this structure, a block layer is formed by a selective epitaxial growth method. Therefore, in the structure of the laser of the present invention, the current injection path is formed in a self-aligned manner, and the problem in the conventional laser of FIG. 5 is solved.

(Example) Next, an Example is given and this invention is demonstrated in more detail. FIG. 1 is a sectional view showing the structure of an embodiment of the present invention, and FIG. 2 is a drawing showing the manufacturing process of this embodiment. In the manufacture of this embodiment, first, a mesa in the (011) direction is formed on a GaAs (100) substrate [FIG. 2 (a)]. Next, using the dielectric mask 8 used at the time of forming the mesa as a mask for the selective epitaxial growth method, the current blocking layer 4 made of GaAs is formed so as to cover only the mesa side surface and the mesa bottom surface [second
Figure (b)]. Then, after removing the dielectric mask 8 used for the mesa formation and the selective epitaxial growth, a double hetero structure including a buffer layer is formed as in the laser of FIG.
It is formed by the MOVPE method. First, after removing the dielectric mask 8, a buffer layer 7 made of GaAs is laminated on the entire surface [FIG. 2 (c)]. At this time, the side surface of GaAs stacked on the mesa holds the (111) B surface. Next, this (111) B
A clad layer 2 made of AlGaInP or AlInP and an active layer 1 made of GaInP are laminated on a GaAs mesa having a face as a side face [second
(D)], and subsequently, the cladding layer 3 made of AlGaInP or AlInP and the cap layer 5 made of GaAs [FIG. 2 (e)] are laminated to form a double hetero structure. The semiconductor laser of FIG. 1 can be manufactured by the above steps.

The characteristic of AlGaInP-based materials is that the AlGa that forms the cladding layers 2 and 3
InP or AlInP is (1
00) is stacked at almost the same growth rate as on the plane,
Since GaInP that becomes the active layer 1 is hardly laminated on the (111) B plane, a BH structure is produced only by MOVPE growth. This means that neither the AlGaAs layer that becomes the cladding layers 2 and 3 nor the GaAs layer that becomes the active layer 1 is laminated on the mesa side surface of the (111) B plane [Reference: S61 Autumn Applied Physics Society] Lecture Proceedings 27P-T-14, pp160].

The laser of FIG. 1 of the present invention solves the two problems in the conventional structure of FIG. First, the first point is the problem of the structure of FIG. 5 such as higher-order mode excitation, lower kink level, higher threshold current, lower yield, and lower reliability due to mask misalignment in the Zn diffusion process. ,
In the laser of FIG. 1, since the current block layer is formed in a self-aligned manner by the selective epitaxial growth method, there is no problem of mask misalignment, the current injection path is formed with good uniformity and reproducibility, the yield is high, and the reliability is high. Laser can be manufactured. Secondly, in the laser shown in FIG. 5, since the wafer after the double hetero structure is subjected to a high temperature treatment called Zn diffusion step, mutual diffusion of impurities during Zn diffusion, deterioration of crystal quality of the active layer, etc. However, in the laser of FIG. 1, the current injection mechanism was already formed before the formation of the double heterostructure.
That is, since the block layer is formed, the problem worried about the laser in FIG. 5 is improved.

Next, the manufacturing method of the embodiment shown in FIG. 1 will be described more specifically with reference to FIG. On the p-type Zn-doped GaAs (100) substrate 6, a 0.2 μm-thick SiO ₂ film stripe (011)
Direction, and using this as a mask, H ₂ SO ₄ and H ₂
Etching with a mixed solution of ₂ O ₂ and H ₂ O,
A (011) direction mesa was formed. The height of the mesa was 4.0 μm. Next, the SiO ₂ mask 8 used for the mesa etching
As a mask for the selective epitaxial growth method.
By the VPE method, a current blocking layer made of Se-doped GaAs having a thickness of 1.0 μm was laminated so as to cover only the side surface and the bottom surface of the mesa. Once taken out from the MOVPE device, HF
The SiO ₂ mask 8 was removed with and the sample was again introduced into the MOVPE apparatus. Then, a buffer layer 7 made of Zn-doped GaAs having a thickness of 2.5 μm is laminated on the mesa substrate by a low pressure MOVPE method to form a new mesa having a (111) B surface on the side surface of the mesa, and then a thickness of 1.0 is formed. μm Zn-doped (Al _0.4 Ga _0.6 ) _0.5 I
n _0.5 P clad layer 2, 0.1 μm thick undoped Ga
_0.5 In _0.5 P active layer 1, 1.0 μm thick Se-doped (A
l _0.4 Ga _0.6 ) _0.5 In _0.5 P clad layer 3, thickness 0.1
The cap layer 5 made of Se-doped GaAs having a thickness of μm was laminated in this order to form the laser structure of the present invention.

Although the above-mentioned embodiment was manufactured by using the low pressure MOVPE method as the selective epitaxial growth method, the semiconductor laser of the present invention can be any crystal as long as the GaAs block layer can be selectively laminated on the portion other than the dielectric mask. It can be produced by the growth method without any problems.

(Effects of the Invention) As described above, according to the present invention, the current blocking layer can be formed by the selective epitaxial growth method. Therefore, the drawbacks of the conventional structure as shown in FIG. , A reliable and high quality AlGaInP index guided laser can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a refractive index guided laser which is an embodiment of the present invention, FIG. 2 is a manufacturing process drawing of the laser of FIG. 1 embodiment, FIGS. 3 and 4 are FIG. 5 is a schematic cross-sectional view of a conventional index-guided laser which is inferred from an AlGaAs laser, and FIG. 5 is a schematic cross-sectional view showing a conventional index-guided laser having another structure. 1 ... Active layer, 2,3,3 '... cladding layer, 4 ... Current blocking layer (GaAs in FIGS. 1, 2, and 5 and current injection portion in FIGS. 3 and 4) AlGaInP or AlInP having a larger Al composition than AlGaInP), 5 ... cap layer, 6 ...
... GaAs substrate, 7 ... buffer layer, 8 ... dielectric mask,
9 ... Zn diffusion region.

Claims (1)

[Claims] 1. A GaAs (100) substrate having a mesa in the (011) direction has a buffer layer made of GaAs, and a side surface of the GaAs buffer layer laminated on the mesa has a (111) B plane. A multi-layered heterostructure including a double heterostructure in which an active layer, which is a clad layer that is connected to the upper surface of the mesa and a lower surface of the mesa and is stacked, is sandwiched between the upper surface of the mesa and the lower surface of the mesa is sandwiched. In the semiconductor laser formed on the buffer layer, the clad layer has a larger band gap than the active layer, the clad layer is made of AlGaInP or AlInP, and the active layer is a GaInP layer formed by the MOVPE method. ,
Between the substrate and the buffer layer, there is a current blocking layer made of GaAs that covers only the mesa side surface and the mesa bottom surface of the substrate, and the current blocking layer is a layer formed in a self-aligned manner by a selective epitaxial growth method. A semiconductor laser characterized in that there is.