JPS6248918B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a buried heterostructure semiconductor laser, and particularly to an InGaAsP buried heterostructure semiconductor laser using InP as a substrate.

Buried heterostructure semiconductor laser (BH−
Abbreviated as LD. ) has excellent characteristics such as low oscillation threshold current, stabilized oscillation transverse mode, and ability to operate at high temperatures, so it is attracting attention as a light source for optical fiber communications. For example, Hirao et al. reported on pages 58 to 61 of Electronic Materials Magazine Vol. 18, No. 12, December 1979, that the shape shown in Fig.
We are producing InGaAsP BHLD. by the way,
Compared to AlGaAs-based lasers, InGaAsP-based lasers generally have a drawback in that the oscillation threshold current has greater temperature dependence. In other words, in an AlGaAs semiconductor laser, the oscillation threshold current I _+h is I _+h ocexp
The characteristic temperature T _p expressed as (T/T _p ) is 120~
While it is about 150K, it is 60~60K for InGaAsP system.
It is small at around 70K, and the temperature dependence of the oscillation threshold current is large. Furthermore, for InGaAsP BH−LD, 40
Since the leakage current flowing through the p-n junction of InP around the active layer increases at temperatures above about 40°C, the characteristic temperature in FIG. T _p decreases to 30-50K. Therefore, to prevent leakage current,
In FIG. 1, between the current block 107 and the n-type cladding layer 102, there is a p-type layer connected to the side surface of the active layer.
An InP current blocking layer 106 is provided to cover the mesa side surface.
By forming the pnpn multilayer structure, it is possible to maintain the characteristic temperature T _p at around 70K up to around 80°C.

By the way, in the manufacturing process of the BH-LD shown in FIG. 1, the p-type InP current blocking layer 106 is replaced with InGaAsP.
In order to form a layer connected to the side surface of the active layer 103, it is necessary to precisely control the etching depth when etching into an inverted mesa shape and the growth thickness of the p-type InP current blocking layer 106. The conventional liquid phase epitaxial growth method and the mesa etching method using a Br methanol-based etching solution do not necessarily provide sufficient controllability, and it is difficult to place the current blocking layer 106 at a desired position on the side surface of the active layer. It is difficult to form it with good reproducibility. Therefore, the InGaAsPBH shown in Figure 1
This results in poor LD production yields.

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned drawbacks, an object of the present invention is to provide a method for manufacturing an InGaAsPBH-LD with a high yield, which has low leakage current to portions other than the active layer, and therefore has excellent temperature characteristics.

According to the present invention, at least an n-type InP substrate having a plane orientation of (100) or near (100)
In _1-x Ga _x As _1-y P _y (0<x<1,0y1) Striped diffusion protection along the <011> direction on the surface of a multilayer structure wafer in which semiconductor layers including an active layer are laminated. After forming the mask, the p-type impurity is
A step of selectively diffusing In _{1 -x} Ga _x As _{1-y P y} deeper than the active layer _, and partially or entirely of the selectively diffused p _- type impurity region A process of chemically etching up to the active layer to form mesa stripes parallel to the <011> direction of the multilayer film structure, and an n-type
In _1-x ′Ga _x ′As _1-y ′P _y ′(0x′<x, y<y′1
)
After laminating the current blocking layer, p-type
In _1-x ″Ga _x ″As _1-y ″P _y ″(0x″＜1,0＜y″
1) A method for manufacturing a buried heterostructure semiconductor laser is obtained, which includes the following steps: 1) an epitaxial growth step in which a buried layer is continuously laminated over the entire surface.

Before explaining the examples, we will introduce InP with (100) plane orientation.
The stacked-layer shape when a mesa stripe formed on a substrate along the <011> direction is filled with an InP layer by liquid phase epitaxial growth will be briefly explained using a diagram. FIG. 2 shows a perspective view showing the growth shape of InP grown on a mesa substrate. Height 0.5μm,
InP substrate 2 with mesa stripes 2 μm wide
When growing an InP epitaxial layer 202 on 01, as described by the authors in Japanese Patent Application No. 55-123261, the growth conditions shown in FIG.
It is possible to grow as shown in b and c. That is, the InP epitaxial layer grows continuously on the mesa side surface and the flat surface, although the film thickness becomes thinner in the middle, but it is not laminated on the mesa top surface. like this
The growth shape of the InP epitaxial layer is convenient for fabricating a current confinement type InGaAsP BH-LD. By the way, if the part other than the mesa stripe of n-type InP is made into a p ⁺ layer by p-type impurity diffusion, by growing an n-InP layer using the growth method shown in Figure 2b, this part becomes an npn structure, and the forward bias can be applied. When applied, the current can be concentrated only in the mesa portion, resulting in less leakage current, and is therefore effective in producing a BH-LD with excellent temperature characteristics.

FIG. 3 shows a cross-sectional view showing a method of manufacturing a preferred embodiment of the present invention. _First , in FIG. 3, an n-InP buffer layer 302 (Te doped, thickness _{5 μm) is formed on an n-InP substrate 301, a non-doped In 0.70 Ga 0.30 As 0.65 P 0.35} active layer 303 ( Wavelength 1.3
As a protective mask for selective diffusion of p-type impurities, a normal InGaAsP-InP DH wafer with a p-InP cladding layer 304 (Zn doped, 0.4 μm thick) was sequentially laminated.
Deposit a SiO ₂ CVD film of approximately 0.3 μm. A photoresist stripe with a width of 4 .mu.m is formed along the <011> direction by a conventional photolithography method, and this is used as a mask for etching using hydrofluoric acid, leaving a selective diffusion protection mask 305. Next, Zn is diffused as a p-type impurity to a depth of approximately 1.2 μm to form a p-type impurity.
A shaped diffusion layer 306 is formed. At this time, as shown in the figure, the lower part of the selective diffusion protection mass 305 has a width of 2 to 3 cm.
An undiffused layer of μm will remain. Next, in FIG. 3, using the selective diffusion protective mask 305 as an etching mask, only the p-InP epitaxial layer is etched using a mixed etching solution of hydrochloric acid:H ₂ O=4:1, which is a selective etching solution for InP. Etching. After that, the S _i C ₂ mask was removed and further etching was performed using bromomethyl etching solution.
By etching 0.2 to 0.3 μm, the height including the active layer 307 of BH-LD is 0.6 μm as shown in the figure.
A mesa 308 of m is formed. At this stage, as shown in the figure, there is a p
A type impurity diffusion layer is formed. Next, Figure 3
Embedded growth is performed at As mentioned above, the buried growth is performed under the growth conditions as shown in FIG. 2b. That is, the n-InP current blocking layer 309
(Te doped flat part thickness 0.4 μm) was grown on the area other than the top surface of the mesa stripe, and then a p-InP buried layer 310 (Zn doped flat part thickness 1.5 μm) was continuously laminated on the entire surface, and n-InGaAsP Cap layer 3
11 (Te doped, 0.5 μm thick) is deposited to finish the growth. During buried growth, the p-InP impurity diffusion layer 306 and n-InP which become the current blocking layer are
The p-n junction of the current blocking layer 309 is InGaAsP.
It is formed next to the active layer 307,
It is particularly effective in preventing leakage current in InGaAsPBH-LDs and therefore improving temperature characteristics. Finally, as shown in FIG. 3, the obtained multilayer film wafer is coated with a selected Zn diffusion layer 312 with a width of 8 μm and a depth reaching the p-InP second cladding layer 310.
After forming AuZn ohmic electrode 31 on the p side
3. Form an AuGeNi ohmic electrode 314 on the n-side and cleave it so that the (110) plane becomes the Fabry-Perot cavity plane to fabricate an InGaAsP BH-LD.

FIG. 4 is a perspective view of an embodiment of the present invention manufactured in this manner. p- to n-InP substrate 401
An InP impurity diffusion layer 404 is provided in advance. As shown in the figure, the n-InP current blocking layer 405 is grown except for the upper part of the mesa.
The p-type impurity diffusion layer 408 is n-
p-InP passes through the InGaAsP cap layer 407.
By forming it so as to reach the second cladding layer 406, the current effectively flows only through the InGaAsP active layer 402 portion. The p-n junction between the p-InP diffusion layer 404 and the n-InP blocking layer 405, which serve as current blocking layers, is formed right next to the InGaAsP active layer 402, and as mentioned at the beginning, this is also the case with the InGaAsP BH-LD. This is particularly effective in preventing leakage current, that is, improving temperature characteristics. this
When a bias voltage with positive on the p side and negative on the n side is applied to the InGaAsP BH-LD, the InGaAsP active layer 402
Since the region is a forward bias of the pn junction, radiative recombination occurs in this region, but the other regions are mostly pnpn junctions and exhibit negative resistance characteristics.
Almost no current flows below the turn-on voltage. Therefore, since the current flows concentratedly in the active layer 402, a low oscillation threshold current of about 20 mA was obtained. In the manufacturing method of the present invention, the active layer 40
By selectively diffusing p-type impurities to a depth deeper than 2, and by selectively etching up to the InGaAsP active layer using a selective diffusion protection mask and growing a current blocking layer in areas other than the top of the mesa, an npn reverse bias is created right next to the active layer. Because the layers are formed automatically
The leakage current in the BH-LD is reduced, and therefore the BH-LD has excellent temperature characteristics of the oscillation threshold current.
LD was obtained with good yield.

In the embodiment of the present invention, In _{0.70 Ga 0.30 As 0.65} P _0.35 with a composition of 1.3 μm is used as the active layer, but the invention _is not limited to this _;
In _1-x Ga _x As _1-y P _y mixed crystal (0<x<1,0y
As for the emission wavelength range of 1), the crystal may have any wavelength between 1.1 μm and 1.7 μm. In addition, an n-InP layer (x'=0, y'=
1) was used, but this layer only needs to have the function of concentrating current in the active layer, so an n- layer with a larger energy gap than the active layer is used.
In _1-x ′Ga _x ′As _1-y ′P _y ′ layer, i.e. active layer
In _1-x Ga _x As _{1-y P} 0x′<x, y<y′ for y
1 or a semi-insulating In _{1 -x} ′Ga _{x ′} As 1 _{- y} ′P _{y ′} layer. I can't help it. The p-type InP buried layer is p-type regardless of the energy gap of the active layer.
In _1-x ″Ga _x ″As _1-y ″P _y ″(0x″＜1,0＜y″
1) It is okay to use layers.

The present invention is a manufacturing method that can obtain a current blocking layer with good reproducibility to improve the temperature characteristics of InGaAsP BH-LD.
It has the characteristic that the manufacturing yield of LDs can be significantly improved.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a conventional InGaAsP BH-LD, Figure 2 is a diagram showing the growth shape when a mesa-shaped substrate is filled with an InP layer, and Figure 3 is a cross-sectional view showing the manufacturing method according to the present invention. , FIG. 4 is a perspective view of a BH-LD obtained by the manufacturing method of the present invention. In the figure, 101 is an n-InP substrate, 102 is an n-
InP buffer layer, 103 is InGaAsP active layer, 10
4 is p-InP cladding layer, 105 is p-InGaAsP
Electrode layer, 106, p-InP current blocking layer, 10
7 is an n-InP current blocking layer, and 108 is an n-InP current blocking layer.
InGaAsP layer, 109 is S _i O ₂ film, 110 is p-type ohmic electrode, 111 is n-type ohmic electrode, 2
01 is (100) InP substrate, 202 is InP epitaxial growth layer, 308 is mesa stripe, 310 is p-InP second clad layer, 311 is n-GaInAsP
312 is a p-type impurity selective diffusion layer; 313 is a p-type impurity selective diffusion layer;
AuZn ohmic electrode, 314 is _{AuGe-Ni ohmic electrode, 402 is In 0.70 Ga 0.30 As 0.65 P 0.35 active layer , 404 is p -} InP impurity diffusion layer, 405 is n
-InP current blocking layer.

Claims (1)

[Claims] 1 At least an InP substrate of the first conductivity type whose plane orientation is (100) or near (100)
In _1-x Ga _x As _1-y P _y (0<x<1,0y1) Striped diffusion protection along the <011> direction on the surface of a multilayer structure wafer in which semiconductor layers including an active layer are laminated. After forming the mask, a step of selectively diffusing the second conductivity type impurity deeper than the In _1-x Ga _x As _1-y P _y active layer, and partially or whole of the selectively diffused p-type impurity region are performed. A step of etching up to the In _1-x Ga _x As _1-y P _y active layer to form a mesa stripe parallel to the <011> direction of the multilayer film structure, and a step of etching the In 1-x Ga x As 1-y P y active layer to form a mesa stripe parallel to the <011> direction of the multilayer film structure; In _1-x ′Ga _x ′As _1-y ′P _y ′ (0x′<x, y<
y′1) P-type after laminating the current blocking layer
In _1-x ″Ga _x ″As _1-y ″P _y ″(0x″＜1,0＜y″
1) A method for manufacturing a buried heterostructure semiconductor laser, comprising the step of: 1) a growth step of continuously stacking a buried layer over the entire surface;