JPS6393184A - Manufacture of buried semiconductor laser element - Google Patents

Abstract

PURPOSE:To execute the growth process of a BH-VSIS semiconductor laser twice by forming an n-i-p-n junction when a substrate takes a p type and a p-i-n-p junction when the substrate takes an n type during a buried growth process and blocking currents by a reverse bias junction. CONSTITUTION:A V-shaped striped groove is notched to the crystal growth surface of a substrate 1, a p<-> GaAlAs clad layer 2, a p or n-GaAlAs (GaAs) active layer 3, an n-GaAlAs clad layer 4 and an n+-GaAs cap layer 5 are laminated in succession, and multilayer crystal structure for laser oscillation operation in which the active layer 3 is held by double hetero-junction surfaces is liquid-phase-epitaxial-grown. A first buried layer 7 having a conductivity type reverse to the substrate 1 is grown so as not to go beyond the active layer 3 on the side surface of a mesa on the substrate 1 first by the buried growth process of mesa type crystal structure through a liquid-phase epitaxial method as a second crystal growth process, and a high resistance layer is grown as a second buried layer 8. A third buried layer 9 having the same conductivity type as the substrate 1 and a fourth buried layer 10 having the conductivity type reverse to the substrate 1 are laminated in succession and grown.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for manufacturing a low-threshold buried semiconductor laser device with a small leakage current flowing through a buried region.

<Prior art> In conventional semiconductor laser devices, BH (Burn
A semiconductor laser having an iED (heterostructure) structure is optimal. The BH type semiconductor laser shown in FIG. 2 has a mesa-shaped double heterojunction structure in which a laser oscillation active layer 3 is sandwiched between cladding layers 2 and 4 from both sides on a substrate 1. Both the left and right sides are filled with crystals that have a lower refractive index and a larger forbidden band width than the active layer,
Furthermore, since the oxide film 14 is interposed at the interface with the electrode 11 to constrict the current, light and carriers are completely confined in the mesa active layer 3, and as a result, the laser beam supplied via the electrodes 11 and 12 Oscillation threshold current is 10-20mA
It becomes a low value.

However, the conventional BH type semiconductor laser device has a drawback that it oscillates in a high-order transverse mode unless the refractive index of the buried layer 13 and the waveguide width W corresponding to the mesa width are controlled to optimum values. Therefore, there are many restrictions on manufacturing conditions, and the waveguide width W is as narrow as 2 μm or less, so the laser resonant end face is easily destroyed even at a relatively low output.

In order to improve the drawbacks of the conventional BH laser mentioned above,
In a VSIS type semiconductor laser as shown in FIG.
A semiconductor laser called an H-VSIS laser has been proposed. This semiconductor laser takes advantage of the VSIS semiconductor laser's characteristic of stable fundamental transverse mode oscillation, and has a distance of 20m.
It has the great advantage of having a low threshold current of less than A. However, the conventional BH-VSIS type semiconductor laser as shown in FIG.
Since the current blocking layer 6 is grown, three crystal growth steps are required including the growth of the double heterojunction structure and the buried growth. Incidentally, it is desirable from the viewpoint of reproducibility and mass production that the number of times of this crystal growth is as small as possible.

<Object of the Invention> In view of the above-mentioned problems, the present invention eliminates the need for the growth of an n-GaAs current blocking layer in the first crystal growth step, thereby improving the H-VS.
An object of the present invention is to provide a method for manufacturing an IS type laser device.

<Example> In the present invention, when the substrate is p-type during the buried growth process, n1p
If the substrate is n-type, create a pinp junction.
The current is blocked by a reverse bias junction of IP or PIN, and will be explained in detail below according to an embodiment. FIG. 1 is a schematic structural diagram of a BH-VSIS laser for explaining one embodiment of the present invention.

After V-shaped stripe grooves are carved on the crystal growth surface of the p-GaAs substrate 1, p-GaA/As is formed on the crystal growth surface.
Cladding layer 2, p or n-G a A I A 5 (
GaAs) active layer 3, n GaAlA3 cladding layer 4
, n+-GaAs cap layer 5 are sequentially stacked to form the active layer 3.
A multilayer crystal structure with laser oscillation action is grown by liquid phase epitaxial growth, in which the crystals are sandwiched between double heterojunction surfaces. The above is the first crystal growth process. Next, the left and right sides of this multilayer crystal are etched to remove the GaAs substrate 1 as well, resulting in a mesa-type crystal structure centered on the stripe groove. Furthermore, as a second crystal growth process, a first buried layer 7 with a conductivity opposite to that of the substrate 1 is placed on the mesa side surface of the active layer 3 in a buried growth process of a mesa type crystal structure using the LPEC (liquid phase epitaxial) method. will grow so as not to exceed.

This is achieved by appropriately reducing the degree of supersaturation of the solution. Next, a high resistance (i) layer is grown as the second buried layer 8. This high resistance layer can be easily realized using undoped GaAJAs having a sufficiently large k1 composition ratio.

Subsequently, a third buried layer 9 of the same conductivity type as the substrate 1 and the substrate 1 are formed.
A fourth buried layer 10 of the opposite conductivity type is sequentially stacked and grown. The first to third buried layers 7 to 9 do not grow on the cap layer 5 because the growth time is short. The fourth buried layer 10 is grown for a long time so that it is also grown on the cap layer 5 so that the entire surface becomes flat. The first buried layer 7 is preferably made of GaAA'As, which does not absorb laser light.

This is because turn-on of the pnipn (or npinp) structure is less likely to occur. The third buried layer 9 is made of GaAs.
But Ga/'l! Either As may be used. Fourth buried layer 1
0 is preferably GaAs in order to lower the ohmic resistance.

When the BH-VSIS laser of the present invention was actually manufactured, the threshold current was 20 mA, the same as the conventional BH-VSIS laser with the current blocking layer 6, at an oscillation wavelength of 830 nm.

<Effects of the Invention> According to the present invention, only two growth steps are required for a BH-VS IS semiconductor laser, and the substrate conductivity type can be either p-type or n-type.

Note that the semiconductor laser device obtained by the present invention is not limited to the above-mentioned BH-VSIS laser, but can also be applied to other BH lasers. In addition to GaAA'As-based BH, InGaAsP-type, InGaAsP-based, etc.
It can also be applied to lasers.

The growth method is LPE (liquid phase epitaxial).
MOCVD (metal organic pyrolysis) method, VPE (vapor phase epitaxial) method, MBE (molecular beam epitaxial) method, etc. may be used.

[Brief explanation of the drawing]

FIG. 1 shows a BH-VSI for explaining one embodiment of the present invention.
It is a structural diagram of an S laser. FIG. 2 is a structural diagram of a conventional BH laser. FIG. 3 is a structural diagram of a conventional BH-VS IS laser. DESCRIPTION OF SYMBOLS 1... Substrate, 2.4... Clad layer, 3... Active layer, 5... Cavity layer, 6... Current blocking layer, 7...
・First buried layer, 8... Second buried layer, 9... Third buried layer, 10... Fourth buried layer, 11.12... Electrode, 1
3... Conventional buried layer, 14... Oxide film.

Claims (1)

[Claims] 1. A step of epitaxially growing a multilayer crystal structure having an active layer for laser oscillation on a crystal growth surface including stripe grooves carved on a substrate, and epitaxially growing a buried layer on both sides of the multilayer crystal structure, 1. A method of manufacturing a buried semiconductor laser device, comprising the steps of: forming a reverse bias junction in a buried layer in contact with the active layer, and making the buried layer in contact with the active layer a high-resistance layer.