JPH0634427B2 - Semiconductor laser manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an AlGaInP-based semiconductor laser having an emission wavelength in the visible light band (600 nm band).

(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. One of the largest uses of the AlGaInP-based semiconductor laser is an optical disc, but in order 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 a gain (or loss) waveguide type to a refractive index waveguide type. , Currently,
There is no reported example of a refractive index guided laser in an AlGaInP semiconductor laser. Therefore, here, as a conventional technique, an AlGaInP-based bending-index waveguide laser, which can be analogized from a lateral mode control structure of an AlGaAs-based semiconductor laser,
And A of Japanese Patent Application No. 62-189839, which is the invention of the present inventor.
The lGaIP-based index-guided laser is taken up.

First, FIG. 3 and FIG. 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 that is usually manufactured by metalorganic pyrolysis vapor phase epitaxy (hereinafter abbreviated as MOVPE method).
After removing the clad layer 3, a clad layer 3 ′ is laminated on the entire surface to form a current injection path. In FIG. 4, contrary to FIG. 3, the clad layer 3 other than the current injection part is partially thinned. rear,
This is a laser for embedding the block layer 4. In FIGS. 3 and 4, the block layer 4 is made of Al forming a current injection portion.
AlGaInP or AlInP having an Al composition larger than that of GaInP is used, and a difference in actual refractive index is provided between the current injection portion and the non-excitation region (block layer portion). Further, in the structure of FIG. 4, room temperature continuous oscillation has been reported in a loss-guided laser in which the block layer 4 is GaAs [Reference: Exfended Abstracts of the 18th Conference on Sol.
id State Derices and Materials, Tokyo, 1986, PP, 153-
156]. However, the structural lasers shown in FIGS. 3 and 4 have the following structural or fabrication problems.

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. High resistance at the growth interface poses a problem. Further, since this regrowth interface is located very close to the active layer and has a high optical density during laser oscillation, many defects introduced into the regrowth interface significantly deteriorate the reliability of this laser. Also, the fourth
For the laser shown in the figure, the AlGaIn layer to be the block layer 4
There are the following problems when re-growing P or AlInP. That is, in FIG. 4, when AlGaInP or AlInP to be the block layer 4 is stacked by selective epitaxial growth by the MOVPE method, the deposition of polycrystalline lumps on the dielectric film to be the selective mask is
Selective embedding becomes very difficult because it increases rapidly with increasing composition.

Next, as a structure for solving the problems of the lasers shown in FIGS. 3 and 4, the laser of Japanese Patent Application No. 62-189839 mentioned above is shown in FIG. First, the structure of this laser will be described. G
The mesa 10 in the (011) direction is formed on the aAs (100) substrate 6, and then the buffer layer 7 made of GaAs is formed on the mesa 10.
Are stacked. At this time, since the growth rate depends on the plane orientation, the side surface of the stacked GaAs on the mesa 10 is (111) B.
It is known that the surface is retained, and eventually the growth on the mesa 10 ends in a triangular shape [Reference: S61 Autumn Proceedings of the Japan Society of Applied Physics 27P-T-14, PP, 160]. Next, on the GaAs mesa having the (111) B surface on its side surface, AlG
clad layer 2 made of aInP or AlInP, GaI
nP active layer 1, AlGaInP or AlInP
Then, the clad layer 3 and the current blocking layer 4 made of GaAs of the same conductivity type as the substrate 6 are sequentially grown by the MOVPE method to form a double hetero structure. At this time, paying attention to the stacking on the side surface of the mesa, the AlGaInP to be the kerad layers 2 and 3 is formed.
Then, the mesa side surface of the (111) B plane and the mesa top surface and the mesa bottom surface of the (100) plane grow at the same growth rate. This is very different from the state of stacking of AlGaAs series. In the case of the AlGaAs system, the growth to the side surface starts only after the mesa side surface is displaced to some extent from the (111) B surface due to the creeping up from the bottom surface. On the other hand, in GaInP which is the active layer 1, the growth rate on the (111) B plane is extremely slower than the growth rate on the (100) plane. Therefore, by first laminating the buffer layer 7 made of GaAs, a new mesa structure having the (111) B plane on the side surface is formed, and then by laminating the double hetero structure having GaInP as the active layer 1, GaIn at the top of the mesa
A semiconductor laser having a buried hetero (BH) structure is formed in which the P active layer 1 is buried with AlGaInP or AlInP cladding layers 2 and 3. Then, finally, the current injection path is formed by utilizing the inversion of the conductivity type by Zn diffusion.
The laser shown in FIG. 5 is a bending-index waveguide type semiconductor laser that is manufactured by skillfully utilizing the plane orientation dependence in MOVPE growth of AlGaInP-based material, which is a problem in the lasers shown in FIGS. 3 and 4. In addition, problems such as oxidation of the high Al composition layer and defective stacking have been improved.

(Problems to be Solved by the Invention) However, on the other hand, the laser of FIG. 5 has the following problems. First, as a first point, in the structure of FIG.
Since the inversion of the conductivity type of the cap layer by Zn diffusion is used as the current injection mechanism, the step of forming the current injection path after forming the double hetero structure becomes complicated. In addition, characteristic deterioration is likely to occur due to mask misalignment in the Zn diffusion window opening process, and in particular, there is a concern that the kink level may decrease due to higher-order mode excitation, the threshold current may increase, and the yield may decrease and the reliability may deteriorate. The second point is that the structure of FIG. 5 has a high temperature heating step of Zn diffusion after the formation of the double hetero structure, so that there are problems such as mutual diffusion of impurities during Zn diffusion and deterioration of the crystal quality of the active layer 1. Become. Further, as a third point, in the laser structure of FIG. 5, a double hetero structure is formed on the mesa 10 formed on the GaAs substrate 6, so that the final shape is such that the upper part of the mesa having the GaInP active layer 1 is outside the mesa. Since the protrusions are larger than those in the flat portion, when the heat sink is assembled with the joint facing downward, a large stress is exerted, which may adversely affect the reliability.

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

(Means for Solving Problems) A method for manufacturing a semiconductor laser provided by the present invention in order to solve the above-mentioned problems is described in (01) on a GaAs (100) substrate.
1) The step of forming two grooves parallel to each other by etching, and the entire surface except the upper surface of the mesa formed between the two grooves is covered with a current blocking layer made of GaAs by the LPE method. A step of stacking a buffer layer made of GaAs on the substrate with the current blocking layer by MOVPE, a step of stacking a first cladding layer made of AlGaInP or AlInP on the entire surface, and
Of the active layer made of GaInP having a smaller forbidden band width than the clad layer on the top surface of the mesa, the bottom surface of the groove, and the flat portions other than the mesa and the groove, and laminating the active layer with a forbidden band width larger than that of the active layer. A step of laminating a second cladding layer made of AlGaInP or AlInP on the entire surface, and GaA
laminating a cap layer made of s on the second clad layer in this order.

(Operation) FIG. 2 shows a cross-sectional view of a refractive index guided AlGaInP based semiconductor laser manufactured by the method of one embodiment of the present invention, and FIG. 1 is a process drawing of the manufacturing method of the embodiment.
The fifth feature of the semiconductor laser manufacturing method of the present invention is as follows.
The laser shown in the figure forms a current injection path by utilizing the inversion of the conductivity type of the cap layer by Zn diffusion after the formation of the double hetero structure. In addition, by taking advantage of the buried growth characteristics of the LPE method, between two parallel grooves formed in the substrate,
It is possible to selectively bury the entire surface except the upper surface of the mesa with a current blocking layer made of GaAs to form a current injection furnace in a self-aligned manner [Reference: I. Mito etali: 'Double chan
nel planar buried heterostructire laser diode with
effective current confinement ', Electron. Lett., 198
2,18, PP.953-954] Moreover, in the laser of FIG.
Different from the laser shown in the drawing, since the flat portion having the same height as or higher than the mesa is also provided on the outer side of the mesa, the fusion stress at the time of fusion with the bonding down is the fifth. It is significantly reduced compared to the laser in the figure.

First, the semiconductor laser manufacturing method of the present invention will be described with reference to FIGS. 1 and 2. Two parallel grooves in the (011) direction are formed on the GaAs (100) substrate 6 [FIG. 1 (a)]. Next, the GaAs substrate 6 having these two grooves
Is introduced into a liquid phase growth reactor to form a current blocking layer 4 made of GaAs [FIG. 1 (b)]. At this time, if the depth of the two grooves is deepened by 10 parts and the width of the mesa is sufficiently narrowed, LP
As a characteristic of the E growth, it is possible to selectively cover only the portion other than the upper surface of the mesa with the GaAs block layer.

Next, the GaAs substrate with the block layer 4 was introduced into the MOVPE growth apparatus, and the buffer layer 7 was formed in the same manner as the laser of FIG.
A double heterostructure including is formed by the MOVPE method. First, the buffer layer 7 made of GaAs is laminated on the substrate [FIG. 1 (c)]. At this time, Ga stacked on the mesa
The side surface of As holds the (111) B surface. Next, on the GaAs mesa having the (111) B surface on its side surface, Al
GaInP or AlInP clad layer 2, Ga
Active layer 1 made of InP [Fig. 1 (d)], AlGaIn
A clad layer 3 made of P or AlInP and a cap layer 5 made of GaAs [FIG. 1 (e)] are laminated to form a duffle heterostructure. [Fig. 2].

In the above-described manufacturing method, the characteristic of the AlGaInP-based material is that AlGaInP or AlI to be the cladding layers 2 and 3 is formed.
nP is deposited on the mesa side surface of the (111) B plane at a growth rate almost equal to that on the (100) plane, whereas GaInP as the active layer 1 is hardly deposited on the (111) B plane. , MOVPE growth produces a BH structure.

This means that the AlGaAs layer serving as the clad layer and the GaAs layer serving as the active layer are not laminated on the mesa side surface of the (111) B plane [B: S laser [Reference: S
61 Autumn, Proceedings of the Japan Society of Applied Physics 27P-T-14, PP160]. The method of manufacturing the semiconductor laser of the present invention has been described above.

According to the method for manufacturing a semiconductor laser of the present invention, the three problems in the laser having the conventional structure shown in FIG. 5 are solved. First of all, in the structure of FIG. 5, the complicated process of Zn diffusion was required to form the current injection path in the structure of FIG. 5, but in the laser of FIG. 1, it was introduced into the liquid phase growth reactor to grow the GaAs layer. All you have to do is Further, the laser of FIG. 5 has problems such as a decrease in kingbell, an increase in threshold current, a decrease in yield, and a deterioration in reliability due to a mask shift in the window opening process for Zn diffusion. With the laser of
Since the block layer is formed in a self-aligned manner by utilizing the characteristics of LPE growth, there is no problem of mask misalignment and the current injection path is formed with good uniformity and reproducibility. As a second point, in the laser of FIG. 5, after the double hetero structure is formed,
Since there is a high temperature heating step called Zn diffusion, there was a concern about mutual diffusion of impurities during Zn diffusion and deterioration of the crystal quality of the active layer. However, in the laser of FIG. Since the block layer is grown for this purpose, the deterioration of the crystal quality of the double hetero structure due to the high temperature treatment does not occur. Thirdly, in the laser structure shown in FIG. 5, the upper part of the mesa having the GaInP active layer is projected larger than the flat part outside the mesa, so that a large fusion-bonding settle can be obtained when assembled with the joint down. There was a problem of receiving it, but in the laser of Figure 1, outside the mesa,
Since the flat portion has a height equal to or higher than that of the mesa portion, the fusion stress when assembled with the joint down is remarkably reduced as compared with the laser of FIG.

(Example) Hereinafter, the laser manufacturing method of the present invention will be described in more detail with reference to examples. The first is a laser manufacturing process diagram of the present embodiment.
Shown in the figure. In the method of this example, first, parallel grooves in the (011) direction were formed on the P-type Zn-doped GAs (100) substrate 6. The depth of the groove was 4.0 μm. Next, the substrate 6
Was introduced into a liquid phase growth reactor, and a current block layer 4 made of Se-doped GaAs was laminated on the entire surface except the upper surface of the mesa. The thickness of the current blocking layer 4 was 0.8 μm in the flat portion outside the groove. Next, the GaAs substrate 6 with the block layer 4 is attached to the MO
Installed in VPE equipment. Then, a Zn-doped GaA film having a thickness of 2.5 μm was formed on the substrate by a low pressure MOVPE method of 70 Torr.
The buffer layer 7 made of s is laminated and (111) B is formed on the side surface of the mesa.
After forming a new mesa having a surface, Zn-doped (Al _0.4 Ga _0.6 ) _0.5 In _0.5 having a thickness of 1.0 μm is formed.
C cladding layer 2 made of P, 0.1 μm thick non-doped G
a _0.5 In _0.5 P active layer 1, thickness 1.0 μm
Se-doped (Al _0.4 Ga _0.6 ) _0.5 In
_A cladding layer 3 made of _0.5 P and a cap layer 5 made of Se-doped GaAs having a thickness of 1.0 μm were laminated in this order.
The above is the embodiment of the laser manufacturing method of the present invention.

(Effects of the Invention) As described above, in the laser manufacturing method of the present invention, a refractive index guided laser can be obtained by a single MOVPE growth.
A current injection path is formed in a self-aligned manner by introducing selective growth of a block layer, which makes use of the characteristics of the LPE method, prior to MOVE growth into the method of manufacturing an InP-based semiconductor laser, and further, two parallel grooves are formed. By using the substrate that has
Significantly improved fusion stress. Therefore, by adopting the method of the present invention, high quality and high reliability of AlGaIn
It is possible to easily manufacture a P-based bending-waveguide semiconductor laser with good reproducibility.

[Brief description of drawings]

FIG. 1 is a diagram showing a process of manufacturing a refractive index guided semiconductor laser according to an embodiment of the present invention, and FIG. 2 is a schematic sectional view showing a semiconductor laser manufactured according to the embodiment of FIG. FIGS. 3 and 4 are schematic cross-sectional views of a conventional index-guided semiconductor laser, which is inferred from an AlGaAs laser.
FIG. 5 is a sectional view schematically showing a conventional index guided semiconductor laser formed by the MOVPE method. 1 ... Active layer, 2, 3, 3 '... Cladding layer, 4 ... Current blocking layer (GaA in FIGS. 1, 2 and 5)
s, in FIGS. 3 and 4, AlGaI in the current injection portion
AlGaInP or Al whose Al composition is larger than nP
InP), 5 ... cap layer, 6 ... GaAs substrate, 7
...... Buffer layer, 8 ...... Zn diffusion region.

Claims (1)

[Claims] 1. A process of forming two parallel grooves in the (011) direction on a GaAs (100) substrate by etching, and the entire surface other than the upper surface of the mesa formed between the two grooves. ,
The step of coating the current blocking layer made of GaAs by the liquid phase epitaxy method and the Ga by the organometallic pyrolysis vapor phase epitaxy method.
Stacking a buffer layer of As on the substrate with the current blocking layer, and AlGaInP or AlI
a step of laminating a first clad layer made of nP on the entire surface,
GaInP having a band gap smaller than that of the first cladding layer
A step of stacking an active layer consisting of the above on the top surface of the mesa, the bottom surface of the groove, and the flat portion other than the mesa and the groove separately from each other;
A method of manufacturing a semiconductor laser, comprising a step of laminating a second clad layer made of InP on the entire surface and a step of laminating a cap layer made of GaAs on the second clad layer in this order.