JPS6237914B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a buried heterostructure semiconductor laser in which the active layer is surrounded by a semiconductor material having a larger energy gap and a smaller refractive index.

Buried heterostructure semiconductor laser (BH-LD)
Because it has excellent properties such as a low oscillation threshold current, a stabilized oscillation transverse mode, and the ability to operate at high temperatures, it is attracting attention as a light source for optical fiber communications. As shown in Japanese Patent Application No. 56-166666, the inventors of the present application have reliably developed a method other than a mesa stripe that includes an active layer that recombines light and is sandwiched between two substantially parallel grooves. In _1-x Ga _x As y P _1-y /InP BH-LD, which can form a current blocking layer, has excellent temperature characteristics, is less susceptible to damage during various _substrate processing processes, and has improved manufacturing yields. invented. However, in a BH-LD with this structure, if the grooves between the mesa stripes containing the active layer that undergoes light emission recombination are narrow, the growth rate of the current blocking layer is fast in that part, and the p-InP current blocking layer, n- When stacking the InP current blocking layer, the n-InP current blocking layer may grow continuously on the mesa stripe, resulting in a decrease in yield.

An object of the present invention is to eliminate the above-mentioned drawbacks by forming a current blocking layer in advance in areas other than mesa stripes, so that only one current blocking layer needs to be grown, and the manufacturing yield can be greatly improved. The objective is to provide a method for manufacturing BH-LD.

According to the present invention, a multilayer structure semiconductor wafer in which a semiconductor multilayer film including at least an active layer is grown on a first conductivity type semiconductor substrate has two parallel grooves and a mesa stripe sandwiched between them. In a method of manufacturing a buried heterostructure semiconductor laser which is formed and then buried and grown, the method includes a step of etching up to the upper surface of an active layer by a selective etching method to form two parallel grooves; An active layer in two parallel groove portions is formed by a selective etching process and a step of diffusing a second conductivity type impurity into the exposed surface of the groove so that the impurity is diffused deeper than the active layer at the bottom surface of the groove. A method for manufacturing a buried heterostructure semiconductor laser is obtained, which includes the step of melt-backing the semiconductor laser and then depositing a semiconductor current blocking layer of the first conductivity type except on the upper surface of the mesa stripe.

The present invention will be explained below using drawings showing examples.

FIG. 1 shows step-by-step cross-sectional views showing a method for manufacturing a BH-LD according to an embodiment of the present invention. As shown in FIG.
SiO ₂ is applied to _{a multilayer semiconductor laser wafer in which a non-doped In 0.72 Ga 0.28 As 0.61 P 0.39 active layer 103 and a} p-InP cladding layer 104 _of μm composition are laminated in sequence _.
The CVD film 105 is stacked, etched windows are etched flat in the <011> direction using ordinary photolithography, and two windows with a width of 5 μm are etched using a mixed solution of hydrochloric acid and water, which is a selective etching solution for InP. Parallel etching grooves 106 and 107 are formed, and a mesa stripe 108 having a width of 2 to 3 μm is formed between them. Next, as shown in Figure 1b,
SiO ₂ film 105 used as an etching mask
Diffusion of Zn, which is a p-type impurity, while leaving Zn
After forming the diffusion layer 109, it was used as a mask.
The SiO ₂ film 105 is removed. Next, as shown in FIG. 1c, buried growth is performed. An InP melt with extremely low supersaturation was used to expose the grooves.
In _0.72 Ga _{0.28 As 0.61 P 0.39 Only the} active layer is melted back _. It is difficult to form epitaxial growth layers neatly on the surface of the Zn diffusion layer, especially in the case of InP, but in this way Zn was diffused into the In _1-x Ga _x As _y P _1-y layer and then melted back. Later, the epitaxially grown layers can be neatly stacked.
Next, an n-InP current blocking layer 110 is deposited except on the top surface of the mesa stripe 108. If the degree of supersaturation of the melt _{of this n-InP current blocking layer 110 is made sufficiently small, only the In 0.72 Ga 0.28 As 0.61 P 0.39 layer exposed in the groove can be} melted back before lamination. In this way, there is no need to prepare melt for meltback. Next _, over the entire p-InP buried layer 111, a p-In _{0.85 Ga 0.15 As 0.33 P 0.67 electrode} layer 112 having a composition with an emission wavelength of 1.1 μm is laminated to form the desired BH. - Get LD.

In the embodiment of the present invention, a Zn diffusion layer 1 which is a current blocking layer is formed in advance before the buried growth.
By forming 08, it is not necessary to stack two layers, a p-InP current blocking layer and an n-InP current blocking layer, except on the top surface of the mesa, as in the conventional example, and the current blocking layer is made of n-InP. Since only one layer is required, it is unlikely that the current blocking layer will cover the mesa stripe. Also, In _1-x Ga _x As _y P _1-y was thermally damaged before Zn diffusion and buried growth.
By melt-backing the active layer, the effect of thermal damage on the active layer is reduced, and buried growth on the diffusion layer can be performed well, resulting in BH-
The manufacturing yield of LDs has been significantly improved. like this
In the In _1-x Ga _x As _y P _1-y /InP BH-LD, a device with an oscillation threshold current of 10 to 20 mA at room temperature and a differential quantum efficiency of about 60% was obtained with good reproducibility.

The feature of the present invention is that a Zn diffusion layer, which serves as a current blocking layer, is formed in advance before the buried growth of the BH-LD.
In _1-x Ga _x A _sy P _1-y Selectively etched up to the surface of the active layer, and etched the exposed part in the groove during buried growth.
In _1-x Ga _x As _y P _1-y The active layer is melt-backed. Therefore, the current blocking layer deposited during buried growth only needs to be an n-InP layer, so the growth rate in the two trenches sandwiching the mesa stripe is fast, but the current blocking layer is not deposited on the top surface of the mesa. There is less storage, and the manufacturing yield of BH-LD has been greatly improved.

[Brief explanation of the drawing]

FIGS. 1a to 1c are cross-sectional views for explaining one embodiment of the BH-LD manufacturing method of the present invention. In the figure, 101...n-InP substrate, 102...n-
InP _buffer layer, 103 _{... In 0.72 Ga 0.28 As 0.61} P _0.39
Active layer, 104... p-InP clad layer, 105...
SiO ₂ film, 106, 107...etching groove, 10
8...Mesa stripe, 109...Zn diffusion layer, 11
0...n-InP current blocking layer, 111...p-InP
_Buried layer, 112...p _{-In 0.85 Ga 0.15 As 0.33 P 0.67}
Electrode layer 113 is a p-type ohmic electrode, and 114 is an n-type ohmic electrode.

Claims (1)

[Claims] 1 After forming two substantially parallel grooves and a mesa stripe sandwiched between them on a multilayer structure semiconductor wafer in which a semiconductor multilayer film including at least an active layer is grown on a first conductivity type semiconductor substrate. In the method of manufacturing a buried heterostructure semiconductor laser formed by buried growth, the steps include: etching up to the upper surface of the active layer by a selective etching method to form the two parallel grooves; a step of diffusing a second conductivity type impurity into the exposed surface of the etching layer so that the impurity is diffused deeper than the active layer at the bottom surface of the etching layer; 1. A method for manufacturing a buried heterostructure semiconductor laser, comprising the step of melt-backing an active layer and then depositing a first conductivity type semiconductor current blocking layer except for the upper surface of the mesa stripe.