JPS59181081A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To improve the element characteristic by forming a semiconductor multilayer layer having an active layer, a waveguide layer and a clad layer on a semiconductor substrate having a slot, forming the waveguide layer corresponding to the slot, and reversing the conductive type of the active layer. CONSTITUTION:An N type AlGaAs clad layer 43 is formed on an N type GaAs substrate 46 formed with a slot 70, and an N type AlGaAs waveguide layer 45 is further formed. The layer 45 has fast growing velocity on the slot 70, and the thickness becomes large. An N type AlGaAs active layer 1, a P type AlGaAs clad layer 2 and an N type GaAs cap layer 4 are sequentially formed thereon. A P type impurity such as Zn is selectively diffused in the regions 9, 10 in response to the position of the slot 70, the conductive type of the layer 1 is converted from N type to P type, thereby forming a striped oscillation region.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser element used as a light source for optical fiber communication, a light source for viewing information on various recording media, a light source for reading information, and the like.

In any of these applications, semiconductor devices are required to have a low threshold current, high external quantum efficiency, and long life. However, with the prior art, it has been difficult to obtain all semiconductor laser devices that are excellent in both device characteristics expressed by threshold current and external quantum efficiency, and lifetime.

First, conventionally proposed semiconductor laser devices will be explained, and which points have problems will be clarified.

The volume of the oscillation region is minute, and the device structure selectively injects current into it, allowing for efficient oscillation.

Semiconductor laser devices with excellent device characteristics such as threshold current value and external differential quantum efficiency have been realized. However, most of them have a structure in which one oscillation region is exposed on the reflective surface, and deterioration occurs due to this exposed region. There are two types of mechanisms for this deterioration. One is that the oxidation reaction progresses in the region upon optical excitation by oscillated light, and the device characteristics gradually deteriorate. This is a deterioration that occurs instantaneously when the reflective surface crystal in the area is damaged by the highly concentrated energy of the oscillation light when operated with a large optical output. The semiconductor laser elements in each building, which have a structure in which the oscillation region is exposed on the reflective surface, have a limited lifetime due to the occurrence of these deteriorations, and are also limited in the amount of optical output that can be operated. The progression of deterioration has been suppressed by reinforcing the reflective surface with a transparent electrically shielding film, and the saw table has been lengthened, but sufficient effects have not been achieved.

In response to this, a proposal has been made to fundamentally solve the problem of deterioration caused by one reflective surface by adopting a structure in which the light emitting region does not protrude on the reflective surface. FIG. 1 shows a perspective view of a window fist line type semiconductor laser element known as a typical semiconductor laser element having such a structure. FIG. 2 is a sectional view taken along the line AA' in FIG. 1. n-AtXoal-XAS active layer 1
(OkuXku1) and sandwich it from both sides I) Aty
Gal-yAs cladding layer 2 and n'AtyG
A double heterojunction is formed with the cladding layer 3 (x<y<1) and the stripe regions 9 and 10 formed by diffusing p-type impurities, for example Zn.
(In FIG. 2, the diagonal lines are placed in different directions to distinguish them.) All of the current is selectively injected into a part of the active layer 1 to realize laser oscillation. The ends of the stripe region 9 and IO are provided at a sufficient distance from the reflective surface, and the oscillation region is not exposed to the reflective surface. Further, the depth of the stripe region 10 reaches the active layer 1, and the conductivity type of the region is converted from n to p type. Therefore, this region has a narrower forbidden band width and a higher refractive index than other regions of the active layer l that remain n-type. Therefore, the protruding region on the reflective surface of the active layer and its vicinity become transparent to the oscillated light, and the oxidation of the reflection of the shield 11 and the deterioration caused by the optical lateral portion are fundamentally improved. However, in this structure9, while the oscillated light travels back and forth between the oscillation region and the reflective surface, the spatial distribution of the oscillated light, especially in the plane parallel to the active layer, expands significantly9, and the reflected light from the reflective surface It is unavoidable that the efficiency with which the light is returned to the oscillation region decreases. This is because the oscillation region, which also served as a lateral optical waveguide function, is interrupted near one reflecting surface. As a result, only devices with large threshold current values and low external differential quantum efficiency were obtained.

FIG. 3 is a perspective view of a cross-contact transverse junction stripe type semiconductor laser device in which the problem of deterioration caused by a reflective surface is solved by a different structure. FIG. 4 is a cross-sectional view of the same element taken along the line BB'. n-At
Xoal-Air A8 active layer 1 and two n-A
z, Ga1-y As layers 12 and 3 are insulating GaAs
A p-n junction is formed by selectively diffusing p-type impurities into a layer provided on the substrate 16. p
Among the converted regions, the region 20 with a high p concentration serves only as a current path, but the region 21 is created with the p concentration controlled, and the region intersecting with the active layer 1 becomes an oscillation region. becomes. The forbidden band width of this region is narrower than that of other regions of the active layer 1 that remain n-type, as in the case of the window stripe type semiconductor laser.

However, it bends into a crank shape near the first reflecting surface.
The bent portion does not contribute to one oscillation because the axis position is different from that of the main portion. Due to this crank-like structure,
The part that irradiates the two-oscillation light reflection surface is transparent n-AtxG.
Al-XA and the active layer 1 are located therein, so that deterioration of the reflective surface does not occur. However, as in the case of the window-fisted stripe type semiconductor laser, the spatial distribution of the 9-oscillated light expands as it travels back and forth between the oscillation region and the reflective surface, and the return efficiency of the oscillated light from the reflective surface is significantly reduced. As a result, it is inevitable that the device characteristics will deteriorate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor laser device that has ambiguous device characteristics and has a long lifetime.

According to the present invention, a semiconductor substrate having a groove, an active layer of a first conductivity type, a waveguide layer adjacent to the active layer and having a wider forbidden band width and a smaller refractive index than the active layer; a semiconductor multilayer film grown on the grooved side of the semiconductor substrate, comprising first and second cladding layers sandwiching these layers from both sides and having a smaller refractive index than any of these layers; means for selectively injecting a current into an oscillation region of the active layer, the waveguide layer being thicker at least at a position corresponding to the groove; The active layer in a region located at a position corresponding to , excluding the vicinity of a pair of reflective surfaces forming a resonator, is converted to the second conductivity type, and the oscillation region is mainly of the second conductivity type. There is obtained a semiconductor laser device characterized in that the region is converted to .

Next, the present invention will be described in detail with reference to the drawings.

FIG. 5 is a perspective view of the first embodiment of the present invention, and FIG. 6 is a sectional view taken along the line c-c' in FIG. To create this layered structure, an n5 groove with a 7° groove formed in advance is required.
GaA, substrate 46i is used, and n-AtyG is first deposited on it.
43 ax-y As two-layer layers were formed, followed by '
-"ZGal-Z As waveguide layer 45 is formed. Since the growth rate is faster in the recessed portion, a waveguide layer with a thicker layer is obtained at the position above the groove 70. Furthermore, n"XGa
1-XAs active layer 1. p-A/! , yG, 1-yAs2 bond layer 2, and nG2As cap layer 4 are sequentially formed (0(x<1.x<Z(y). 9 and 9 in FIG. A p-type impurity, for example Z
Selectively diffuse n.

The IO region reaches the active layer 1 and changes the conductivity type from n type to p type.
Convert to type. The striped region of the active layer 1 converted to p-type becomes an oscillation region. Since the forbidden band width of this oscillation region is υ smaller than that of the active layer which remains n-type, the portion of the active layer exposed to the reflective surface is not transparent to the oscillation light.
No deterioration occurs due to oxidation of the reflective surface or optical damage. In other words, the saw table is improved to the same extent as the window stripe type semiconductor laser. Not only that, but the semiconductor laser device of this embodiment achieves all of the following excellent device characteristics due to the function of the waveguide layer 45.

Since the active layer 1 is made thin, with a layer thickness of about 0.2 μm or less, the oscillated light seeps out in the layer thickness direction, and the waveguide layer 45. The average refractive index including the double layer 43 is felt. Since the refractive index of the waveguide layer 45 is larger than that of the cladding layer 43, the thicker portion of the waveguide layer 45 has a larger effective refractive index perceived by the oscillation light. Therefore, the oscillated light is guided so as to be focused on the central portion of the groove where the cladding layer 43 has the largest layer thickness. This waveguide structure exists continuously throughout the entire region of the resonator, and also guides the oscillated light between the oscillation region and the reflection surface.

In this part, the spatial distribution of the oscillated light does not spread significantly, and the reflected light is efficiently returned to the oscillation region. As a result, a semiconductor device with a low threshold current value, high external differential quantum efficiency, and excellent device characteristics can be obtained.

FIG. 7 is a perspective view of a second embodiment of the present invention, and FIG. 8 is a sectional view taken along line DD' in FIG. The crystal growth method and impurity diffusion method are generally the same as in the first embodiment described above.

G 2 A s substrate 56 is insulating, substrate 56
The main difference is that each layer that is grown on top of Evita is of n-type, and that the shape of the p-type impurity diffusion region is crank-shaped. The diffusion region 21, except for the region where the bend near the reflecting surface crosses the active layer 1 at a position corresponding to the thicker part of the waveguide layer 45, and the conductivity type of that region is from n-type to n-type. Converted to p-type. The active layer in the region whose conductivity type has been changed becomes the oscillation region. The energy of the oscillation light is smaller than the forbidden band width of the other regions of the active layer 1 that remain n-type, and the part where one oscillation light irradiates the reflective surface has a transparent n -AtxGa, -xA, active layer. 1 is located, no deterioration of the reflective surface occurs.

In addition, the oscillation light is well guided by the function of the waveguide layer 45, and the spatial distribution does not widen even when it travels back and forth between the 9 oscillation region and the reflection surface, resulting in a low threshold current value.

A device with high differential quantum efficiency can be obtained.

Although the present invention has been described above in detail based on two embodiments, the present invention is not limited to these embodiments. In the examples, the case where the thickness of the active layer is uniform and average has been explained, but the layer thickness of the active layer may be thicker at the position corresponding to the groove, or bent, similar to the waveguide layer. The same effect can be obtained even if In addition, for the purpose of setting the 9 reflectance to an arbitrary value and for the purpose of preventing gradual erosion of crystal surfaces due to the atmosphere, 9 reflective surfaces k Sl 0
A similar effect can be obtained by protecting with a dielectric film such as 2 rAt2 oa I s i 3 N 4 . In addition to AtGaA3, the present invention also applies to InGaA, P, InGaP
The present invention can also be applied to semiconductor laser electrons whose active layers are various compound semiconductors composed of a combination of Group III elements and Group II elements, such as .

As described in detail above, according to the present invention, a semiconductor device with excellent device characteristics and a long life can be provided.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a conventional window stripe type semiconductor laser device, and FIG. 2 is a sectional view taken along the line A-A' in FIG.
FIG. 3 is a perspective view of a conventional crank transverse junction stripe type semiconductor laser device, FIG. 4 is a sectional view taken along the line B-B' in FIG. 3, and FIG.
6 is a sectional view taken along the line CC' in FIG. 5, FIG. 7 is a perspective view of the second embodiment of the present invention, and FIG. FIG. 3 is a cross-sectional view taken along arrow D' (in these figures, the shaded area indicates a p-type impurity diffusion region). 1... n-AtxGBl-z As active layer, 2
......p-AtyGa 1-y As cladding layer, 3, 12, 43...-n-AtyGal-y
A6 cladding layer, 4.14-・-・-・n-Ga aA
3 cap layer, 6146--n OBh s substrate, 16.56...Insulating G21 As s substrate,
7.18...N-side ohmic electrode, 8.19
...N-side ohmic electrode, 9.20...
...High concentration p-type region, 10°21...'p-type region 45 □......n AtzOB 1-2 A
s waveguide layer. '-1 -・' Agent Patent attorney Yo Uchihara.

Claims (1)

[Claims] A semiconductor substrate having a groove, an active layer of a first conductivity type, a waveguide layer adjacent to the active layer and having a wider forbidden band width and a lower refractive index than the active layer, and a waveguide layer sandwiched from both sides of these layers 2. Each of these layers consists of a first and second glue layer having a small refractive index, a semiconductor multilayer film grown on the side of the semiconductor substrate with the groove, and one of the active layers. means for selectively injecting all of the current into the oscillation region, the waveguide layer is formed thicker at least at a position corresponding to the groove, and the waveguide layer is formed thicker at least at a position corresponding to the groove in the active layer; The active layer in a region excluding the vicinity of a pair of reflective surfaces forming a resonator is converted to the second conductivity type, and the oscillation region is mainly converted to the second conductivity type. A semiconductor laser device characterized in that it is a region.