JPS6297390A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To form a semiconductor laser element having a refractive index waveguide mechanism, which can be manufactured by an MBE method, when a super-lattice structure is grown on a substrate having a stripe shaped groove, by utilizing tendency that the super-lattice structure offsets groove-shaped irregularities when the width of the groove is narrowed. CONSTITUTION:The pitch of grooves on an irregular surface 2 is made very small. The average thickness of a lightguide layer 4 directly on the irregular surface 2 is thicker than the parts of the lightguide layer 4 at the outer flat surface. Therefore, the refractive index distribution in the parallel direction with an active layer 7 is large at a part directly on the irregular surface 2. The distribution on both sides is small. Thus, a refractive index waveguide is formed within the active layer 7. In this structure, when the thicknesses of a GaAs layer 6 and AlGaAs 5, which constitute the super-lattice structure of the lightguide layer 4, are selected to be suitable values, the equivalent forbidden band width caused by the thickness of the lightguide layer 4 can be made small directly on the irregular surface 2 and can be made large at the outside other than said part. Thus carriers can be effectively confined within the region of the active layer directly on the irregular surface 2.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an index-guided semiconductor laser device that can be manufactured by molecular beam epitaxy.

<Prior art and its problems> In recent years, the application fields of semiconductor lasers such as compact disc players and video disc players have been making remarkable progress, and the demand for semiconductor lasers as signal light sources is rapidly increasing. .

For such applied equipment, semiconductor lasers have important issues of ensuring reliability and stabilizing optical characteristics.
In particular, with regard to stabilization of optical properties, extremely stable properties have been obtained by providing a refractive index waveguide mechanism as the optical waveguide mechanism. A typical type of index-guided semiconductor laser is BH (Burried-Hete).
rostructure) laser, C8P (Chan
nel! ed-8ubstrate Planer)
Laser, VS I S (V-hannej'edSu
(bstrate inner 5tripe) lasers have been proposed and put into practical use. However, most of these index-guided semiconductor lasers use liquid phase growth as a crystal growth method, and effectively utilize the characteristics of the liquid phase growth method. It is difficult to overcome drawbacks such as difficult control of thin layers, poor uniformity, and consequent poor yields.

On the other hand, molecular beam epitaxy (MBE) is attracting attention as a growth method that has a high degree of thin layer controllability and is expected to have good uniformity, in view of the drawbacks of the liquid phase growth method as described above. ing. However, since the growth mechanism of the MBE method is different from that of the liquid phase growth method, the refractive index waveguide type device structure developed by the liquid phase growth method cannot be applied as the element structure of a semiconductor laser.

<Summary of the Invention> In view of the above-mentioned problems, an object of the present invention is to provide a semiconductor laser device having a refractive index waveguide mechanism that can be manufactured by the MBE method. .

As a result of conducting detailed experiments on crystal growth using the MBE method when creating the present invention, we found that when a superlattice structure is grown on a substrate having striped grooves, the substrate has a structure as shown in FIG. If the groove width W of the groove 2 formed on the substrate l is narrow to some extent, especially less than 5oooi, the superlattice structure grown on this substrate l tends to cancel out the unevenness of the groove shape, and the superlattice structure grown on the substrate l shows a tendency to cancel out the unevenness of the groove shape. It was found that flattening occurs. The present invention utilizes this phenomenon to form a refractive index waveguide mechanism in a semiconductor laser device.

<Example> FIG. 1 is a cross-sectional configuration diagram of a semiconductor laser device schematically showing an example of the present invention.

On the growth surface of the n-GaAs substrate 1, 300 striped grooves with a width of 1500× are formed using microfabrication techniques such as etching.
Approximately 2. They are arranged in parallel over the ttm and exhibit periodic uneven surfaces 2.

On the GaAs substrate 1 including the uneven surface 2, a first cladding layer 3 consisting of 1.5 layers and 1 m thick of n-A lo, 3 Gao, . . . As is laminated by the MBE method.

When grown by the MBE method, the uneven surface 2 of the GaAs substrate 1 is carried over to the first cladding layer 3, and therefore the first cladding layer 3 is formed on the GaAs substrate 1.
The surface region immediately above the substrate acid surface 2 becomes an uneven interface 15, and the interfaces on both sides thereof become a flat interface 16. First cladding layer 3
A light guide layer 4 is subsequently laminated thereon. This light guide layer 4 is made by MBE to a thickness of approximately 30 mm.
o, x G d 0. It is composed of a superlattice structure consisting of a large number of IAs layers 6 stacked alternately, and the total thickness is about 2oo.
It is set to oi. By making the light guide layer 4 have a superlattice structure in this way, the uneven shape of the uneven interface 15 existing at the interface of the first cladding layer 3 is canceled out by the superlattice structure, and as shown in FIG. As shown in , the thickness of the light guide layer 4 is thinner in the region of the uneven interface 15 of the first cladding layer 3 where there are no grooves, and thicker in the grooved portion.

An active layer 7 made of GaAs, pA
l! A second cladding layer 8 made of p-GaAs, 3sGaAs, and 6sAS is sequentially grown. After the above growth is performed successively by the MBE method, the cap layer is removed from the MBE apparatus. CVD on 9
A 5i02 film 10 is deposited to a thickness of about 300X according to the method,
By photolithography, the region directly above the uneven surface 2 of this SiO2 film 1O is removed in a stripe shape with a width of 3) tm to form a current path. Next, a P- electrode 11 is placed on the 5i02 film 2 and the cap layer 9, and an n- electrode is placed on the back surface of the GaAs substrate 1.
After forming the electrode 12 by a vapor deposition method, it is made into individual semiconductor laser elements by a sleeve opening method.

By adopting the above structure, the layer thickness in the light guide layer 4 directly above the uneven surface 2 formed on the GaAs substrate 1 changes periodically, but since the pitch of the grooves is aooooi and is very small. For light in the oscillation wavelength range, the average thickness is the thickness of the light guide layer at that portion. Therefore, the average thickness of the light guide layer 4 directly above the uneven surface 2 is thicker than that of the light guide layer 4 in the region exhibiting a flat surface on both sides, so that the refractive index distribution in the direction parallel to the active layer 7 is is large immediately above the uneven surface 2 and becomes small on both sides thereof.

As a result, a refractive index waveguide is formed within the active layer 7.

Furthermore, in this structure, since the optical guide layer 4 has a superlattice structure, each of the semiconductor layers constituting the optical guide layer 4, that is, the GaAs layer 6 and the Ar
By selecting the thickness of GaAs 5 to an appropriate value, the equivalent forbidden band width caused by the layer thickness of the light guide layer 4 directly above the uneven surface 2 and the light guide layers 4 on both sides thereof can be It is possible to be small directly above the uneven surface 2 of the guide layer 4 and to be large outside the uneven surface of the optical guide layer 4, thereby effectively confining carriers in the active layer 7 region directly above the uneven surface 2. becomes possible.

As a result of the above-mentioned effects, stable laser oscillation in the fundamental transverse mode was obtained with a threshold current of 15 mA and an optical output of 10 mW or more in the semiconductor laser device of the above-described example.

<Effects of the Invention> According to the present invention, a semiconductor laser device having a refractive index waveguide mechanism can be manufactured with a high yield using a temporary threshold current using the MBE method.
Moreover, it can be produced by one MBE growth.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the relationship between the striped groove width and the groove shape absorbed by the superlattice layer in the case of semiconductor laser axial growth according to an embodiment of the present invention. l...GaAs substrate, 2... uneven surface,
3... First cladding layer, 4... Light guide layer,
5...AI! GaAa layer, 6-GaAs layer, 7... active layer, 8... second cladding layer,
9... Cap layer, 10... 5i02 film,
11...P-electrode, 12...n-electrode.

Claims (1)

[Claims] 1. In a semiconductor laser device in which an active layer and a cladding layer are sequentially deposited via a light guide layer on a substrate partially having an uneven surface in which a plurality of parallel striped grooves are formed, the light guide layer has a superlattice structure formed by alternately stacking two or more types of semiconductor layers having different compositions, and a layer thickness distribution is imparted to the superlattice structure in the region corresponding to the uneven surface, and the layer of the light guide layer A semiconductor laser device characterized in that the refractive index of the active layer differs depending on a region provided with a thickness distribution and a region other than the region.