JPS5968988A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To enable a large photo output oscillation and facilitate the manufacture by a method wherein shallow groove active regions at two parts are provided by isolation each other in the same plane in the londitudinal direction of a resonator, and a deep groove is provided in the neighborhood of reflection surfaces at both ends of the resonator. CONSTITUTION:The first shallow V-grooves 51 and 52 are formed in parallel at the center region of the resonator of a P type GaAs substrate 10, the second shallow V- groove 53 is formed on its extension, and a deep V-groove 54 is formed in continuity to this groove 53. At the region becoming the other reflection surface in opposition to the reflection surface wherein the groove 54 is formed, the deep rectangular groove 55 is formed in adjacency to the grooves 51 and 52. Next, clad layers are formed in the grooves 51-55, and then active layers, guide layers, clad layers, and cap layers are successively grown. This constitution makes it difficult to generate the chemical reaction with the outside because of no direct exposure of an excited region to the reflection surface and thus enables to block the deterioration due to the photochemical reaction of the reflection surface. Besides, since the neighborhood of the reflection surface is a layer of a band gap which is large to an oscillated light, light absorption is small, optical damages are difficult to generate, and accordingly the large photo output oscillation is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to semiconductor lasers, and more particularly to high optical output semiconductor lasers.

Visible light semiconductor lasers using crystalline materials such as AtGaAs/GaAs can perform continuous oscillation at room temperature with a low threshold and high efficiency, making them ideal as light sources for optical digital audio disks (DAD). Devices using semiconductor lasers are being put into practical use. There is an increasing demand for this visible light semiconductor laser to be used as a light source for optical writing in optical printers and the like, and in order to meet this demand, research and development of visible light semiconductor lasers that can withstand large optical output oscillations is underway.

By the way, conventional AtG with a stripe width of 10 to 20 μm
aAs/GaAs semiconductor lasers are room temperature continuous wave (CW) lasers.
) has an optical output of about 10 mW, and a pulse operation (100 ns width) optical output of 100 mW at 8 degrees is the operating limit.
There is a phenomenon in which the reflective surface is easily destroyed if more optical power is emitted. This phenomenon has long been known as optical damage, and the critical optical power density of this CW operation is IMW/d
Before and after.

Conventionally, attempts have been made to lower the optical output density at the reflective surface in order to obtain a large optical output. That is, enlargement of stripe width, enlargement of active layer thickness, double double heterostructure, etc. have been reported, but in this case.

The increase in threshold current density makes continuous excavation at room temperature difficult. In addition, when operating with a large optical output, the oscillation region expands even if the stripe width is narrow, and the horizontal transverse mode (mode parallel to the active layer) becomes a complex multi-mode. It has become a complex multimodal system. For this reason, the use of high-output semiconductor lasers is limited to obstacle detection, etc., and is not used in laser printers or the like.

On the other hand, a structure in which no current is applied to the vicinity of the reflective surface, leaving it in a non-excited state, and a current is supplied only to the stripe region in the center to make it an excitation region, and the vicinity of the reflective surface becomes a non-excited region that is transparent to the laser beam. A striped semiconductor laser was proposed by the inventors of the present invention in Japanese Patent Application No. 53-18882.

In the case of AtGaAs/GaAs double heterojunction structure,
The active layer in the non-excited region surrounding the excited region is made n-type.

When the part of the active layer that becomes the excited region is made p-type in a stripe shape by Zn diffusion, etc., the band gap of the non-excited region is about 30 to 50 meV with respect to the band gap of the excited region.
Shrink. In this case, the higher the n-type concentration and the higher the p-type concentration, the greater the relative change in bandgap, so the non-excitation region becomes almost transparent to the laser light generated in the excitation region. In this structure, no optical damage occurred even when the optical output exceeded five times the conventional limit optical output. That is, it was confirmed that if the non-excited region is longer than the diffusion length of minority carriers, sufficient effects are exhibited, and these effects are limited to the double heterojunction structure. However, in semiconductor lasers with this structure, the excitation region is impurity-compensated p-type, which not only tends to have large internal absorption losses and a high threshold current, but also shortens the diffusion length, resulting in higher-order transverse modes. The increase in gain is large, and the horizontal transverse mode becomes a high-order multi-mode during operation with a large optical output. Furthermore, when the laser light propagates through the non-excitation region, the light propagates while spreading in a Gaussian distribution, so the light that is reflected by the reflective surface and returns enters the excitation region again, increasing the gain required for laser oscillation. The ratio contributing to the increase (coupling efficiency) becomes low, resulting in disadvantages such as increased loss, increased threshold current, and decreased external differential quantum efficiency.

Furthermore, a structure has been proposed in which the vicinity of the reflective surface is buried with a cladding layer having a larger band gap than the active layer. but,
In this case as well, as with the above structure, when the laser light propagates through the cladding layer, the light spreads and the coupling efficiency decreases, so it has the disadvantage of increasing the threshold current and decreasing the external differential quantum efficiency. In addition, the manufacturing method is complicated, such as etching after crystal growth and burying the region that will become the reflective surface with a cladding layer, and crystal defects also occur at the interface between the buried cladding layer region and the active layer. It had various drawbacks, such as being easy to use and having problems with reliability.

On the other hand, in this structure, if the area near the reflective surface is made transparent, the limit of the large optical output that can operate reliably is 20 ~
It is about 30mW, which is necessary as a light source for optical writing.
It has been difficult to operate reliably and stably with a large optical output of 0 to 60 mW.

The purpose of the present invention is to eliminate these drawbacks, to enable oscillation with a much higher optical power than conventional methods, and to produce not only fundamental transverse mode oscillation but also single-axis mode oscillation, which can be manufactured and reproduced in one growth process. The purpose of the present invention is to provide a semiconductor laser that is excellent in terms of performance and reliability.

The structure of the semiconductor laser of the present invention has a plurality of first grooves parallel to each other in the central portion in the longitudinal direction of the cavity, and a second shallow groove in a part of the extension in the longitudinal direction of the cavity. a semiconductor substrate having deep grooves formed near both incident surfaces at both ends of the resonator;
An active layer and a guide layer having a refractive index lower than that of this active layer are formed on this semiconductor substrate.
．． a multilayer structure sandwiched between second cladding layers, wherein the active regions of the plurality of first shallow trench regions and the active regions of the second shallow trench regions are provided on the same plane and separated from each other. , Ml, 82, a step is provided between the active layer in the shallow trench region and the active layer in the deep trench, and the active layer in the deep trench is made into a non-excited region.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a perspective view of an embodiment of the present invention, No. 21"l) d
3 and 4 are sectional views taken along lines hh: 13-B' and c-c' in FIG. 1, and FIG. 5 is a perspective view of the substrate in FIG. 1.

First, a 5iOz film is applied on a p-type GaAs substrate 10 whose plane is the (100) plane, and a (01
1) Stripe-shaped first windows (51, 52) with a width of 2 μm are placed in the central region in the direction of 200 μm with an interval of 15 μm.
A second window (53) with a width of 2 μm and a length of 50 μm is made, and a second window (53) with a width of 2 μm and a length of 50 μm is located at the center of both in the length direction of the resonator and separated by 10 μm from both, and a second window (53) with a width of 4 μm is made continuously.
A window (54) with a length of 50 μm is formed. Next, when etching is performed using a mixed solution of Br2 and methyl alcohol, the (111)A surface is converted to a side slope (54 degrees 4 degrees with respect to the plane).
4) Grooves 51 to 54 are formed. ■Two first V grooves 51 and 52 with a depth of 1.4 μm are formed in the central region of the resonator in parallel, corresponding to the width of the window made in the 5iQ2 film used as an etching mask. 2 by extension
Book first groove 51. , 52 is formed with a V-groove 53 having a depth of 1.4 μm and a V-groove 54 with a depth of 2.8 μm is formed in the vicinity of the reflecting surface. After removing the 8i02 film, a 3iQ2 film is applied to the entire surface again, and a groove with a width of 30 mm is formed adjacent to the first groove 51, 52 in the area that will become the other reflective surface with respect to the reflective surface on which the V groove is formed.
A stripe-shaped window (55) with a length of 50 μm is opened. At this time, both of the first grooves 51 and 52 are made to be included within the stripe width in the resonator [011] direction. Next, H3PO4, H2O2, CH30H is 1:1
: When etching is performed to a depth of 2.8 μm using a mixed solution of 3, a rectangular groove 55 is formed, and when the SiO2 film is removed,
A substrate 10 necessary for the configuration of the present invention as shown in FIG. 5 is formed.

Next, a p-type AtO, 4GaO, SAs cladding layer 11 is grown to completely fill the shallow grooves 51 to 53 in the central portion and to have a thickness of 0.1 μm at the shoulder portion outside the groove. A flat growth surface can be obtained. Then undoped At011sGaO1B, As activity)v112 is 0
．． Grow to 08 μm. At this time, p-type rad layers 11 are also formed inside the deep grooves near both reflective surfaces. Active, I! i12 grows, and the growth surface of the active layer 12 is located at a depth of 0.5 μm with respect to the flat substrate surface. Next, n-type kto, xt
oao, As guide layer 13 with a thickness of 1.0 μm.

n-type kto, 4 Ga 6.6 As cladding layer 14 at 1.5/Am.

A p-type GaAs cap layer 15 is continuously grown to a thickness of 0.5 μm. At this time, the deep grooves 54 and 55 near both reflective surfaces are completely filled with the guide layer 13.
are the first V groove region 51, 52 or the second V groove region 51, 52, respectively.
A portion of the p-type rad layer 11 grown in the groove region 53, the active layer 12. Adjacent to a portion of the guide layer 13 .

Next, an 8fo2 film 16 is applied to the growth surface, and the first
Windows are formed in the cap layer 15 of the (1) groove regions 51, 52 and the second V-groove region 53 using a photoresist method, and n-type impurity sulfur is added to the cap layer 15 by n-type hto, 4G a 6.6 A s.
Diffusion is performed so that the diffusion front reaches a part of the cladding layer 14. At this time, the diffusion region 17 in the first groove region 51 and 52 and the diffusion region 18 in the groove region 53 of WJ2 are made not to contact each other. After that, an n-type ohmic contact 19. The semiconductor laser of the present invention can be constructed by forming a p-type ohmic contact 20 on the substrate side.

In this embodiment, the first shallow groove 5 in the central part of the resonator
A part of the light that seeps into the first cladding layer 11 from the active layer 12 in the 1.52 part is absorbed by G, which becomes an absorber for the oscillation wavelength.
It reaches the aAs substrate and suffers a large absorption loss. This results in steps of loss and gain, and at the same time each shallow groove 5
The refractive index of the active layer 12 above 1.52 is increased, and a positive effective refractive index difference is formed within the active layer 12, and a refractive index guiding mechanism is formed on each shallow groove, resulting in stable fundamental transverse mode oscillation. I do.

In particular, in this structure, a 14 i shallow groove 51.
In the region 52, a portion of the light leaks from the active layer 12 into the adjacent guide layer 13 and causes laser oscillation, which significantly increases the level of optical damage caused. That is,
A part of the light that seeps out from the active layer 12 during laser oscillation passes through the guide layer 13, which has a wide bandgap relative to the oscillation wavelength, so it is transmitted without suffering any absorption loss, and the light passing through the active layer 12 causes optical damage. However, by reducing the amount of light within the active layer 12, the level at which optical damage occurs can be increased. In this structure, the level of optical damage in each laser oscillation region increases, so the total output power increases in proportion to the i of the first shallow groove 51, 52 which serves as the laser oscillation region. It can be raised to The amount of light that seeps into the guide layer 13 can be changed by changing the refractive index of the guide layer, but in the structure of this embodiment that has an absorption effect, the amount of light that seeps into the guide layer 13 is adjusted and the amount of light that seeps into the guide layer 13 is adjusted. It is also necessary to create a light seepage effect. For this purpose, the first growth on the external flat part of the shallow groove is necessary.
It is desirable to reduce the layer thickness of the cladding layer 11.

Further, in the first shallow groove region 51° 52 at the center of the resonator, a stripe-shaped second shallow groove 53 is formed on the extension of the resonator length.
It has the following features. That is, the active layer 12 corresponding to this striped second shallow groove 53
Carriers are injected into the grooves 51 and 52 to form excitation regions independent of the first shallow grooves 51 and 52. These first shallow grooves 51
．． When the light excited by 52 propagates in the resonator length direction, if there is an excitation region, the light is focused on the excitation region. Therefore, in the structure of the present invention, the excitation light from the laser resonators in the first shallow groove regions 51 and 52 passes through the second excitation region (53) in the light propagation direction, overlaps each other, and forms a single beam. Laser oscillation output can be extracted as the fundamental transverse mode from the reflective surface of the deep groove region adjacent to the second excitation region. At this time, since the laser beams corresponding to the number of laser resonators in the first shallow groove regions 51 and 52 are overlapped with each other, an oscillation light output obtained by multiplying them can be obtained, and large optical output laser oscillation is possible. For example, if the maximum optical output from one first groove is 50 mW, this embodiment allows a large optical output of 100+nW.

When the laser beams from different resonators overlap in the excitation region in this way, the axial modes formed by these resonators also couple, but only the time-axis modes mutually reinforce each other, resulting in a single strong axial mode. become. This axial mode has slight fluctuations within the same active layer, and the axial mode formed by each resonator changes slightly, but the number of mutually reinforcing axial modes is about one, so Single axial mode oscillation can be obtained.

The structure of the deep grooves near both reflecting surfaces in this embodiment has the following characteristics. Namely.

In this case, during crystal growth, the active layer is formed not only in the shallow groove region but also in the deep groove regions 54 and 52 near both reflective surfaces, but a step is created due to the difference in the depth of the groove in the resonator length direction. If the active layer is large, the active layer tends to break off at that part and grow easily. Note that even if the active layers are connected, the active layer 12 inside the deep groove is a non-excited region, so the light passing from the shallow groove to the active layer in the deep groove is from 150cm'' to 200c=
In order to undergo absorption loss over a period of 30 minutes, the laser oscillation is emitted by traveling straight through the deep groove guide layer, rather than as a path for the laser oscillation.

In particular, in this structure, there is a deep groove 54 adjacent to the second shallow groove 53 near one reflecting surface, and a plurality of shallow grooves 54 adjacent to the plurality of first shallow grooves 51 and 52 near the other reflecting surface. 55 deep grooves are formed with a width that includes all of them. 1st. The active layer 12 in each of the second shallow groove regions 51 to 53 has a guide layer 13 in the deep groove region at the boundary with the deep groove.
Adjacent to part of. Therefore, the laser oscillation light travels straight through the guide layer 13 in the vicinity of both reflective surfaces, but this guide layer is transparent to the laser oscillation light and the absorption loss of the light can be completely ignored. For example, at the oscillation wavelength λ=0.78 fim, when Ato, zy Gao, and ys AS guide layers are used, the energy difference is 17011 eV or more, making it possible to oscillate with a low threshold.

In addition, in the structure of the present invention, there is a guide J@13 that serves as a light guide mechanism near the reflecting surface, and the light travels while being confined within this guide layer, and this light guide mechanism prevents the effect of light overlapping. This facilitates single transverse mode oscillation. As this laser light travels through the guide layer in the deep groove region, it also spreads in the vertical direction, and the spread angles of the laser oscillation light in the vertical and horizontal directions become almost circular, resulting in a nearly circular oscillation light that is coupled to the optical system. Efficiency also increases.

Furthermore, the structure in which the laser oscillation light passes through the vicinity of the internal reflection surface can dramatically increase the level of damage to the reflection surface (COD). In other words, in a normal semiconductor laser, the end face of the active layer, which becomes the excitation region due to carrier injection, is exposed as a reflective surface, where surface recombination occurs, forming a depletion layer and reducing the band gap, resulting in large optical output oscillation. When this occurs, light absorption occurs due to the reduced bandgap, which generates heat and rises in temperature to near the melting point, eventually causing optical damage. On the other hand, in the structure of the present invention, the laser oscillation light passes through the guide layer with a band gap difference of 170 meV or more in the vicinity of both end faces, which are the light reflecting surfaces. Therefore, optical damage is less likely to occur and high optical output oscillation is possible. Furthermore, the light at the center of the resonator length penetrates into the guide layer and oscillates as a laser, so
f Quantum Elec-tronics,
The destruction phenomenon occurring inside the active layer due to large optical output oscillation, as reported by Yonezu et al. in Vol.

As explained above, the semiconductor laser according to the present invention has
Compared to a normal semiconductor laser in which the excitation region is directly exposed to the reflective surface, chemical reactions with the outside are less likely to occur, and deterioration due to optical reactions on the reflective surface can be prevented. In addition, since the area near this reflective surface is a layer with an extremely large bandgap relative to the oscillated light, light absorption is low and optical damage is less likely to occur, allowing for large optical output oscillation, making the overall optical output much lower than before. Compared to the laser array of Further, this structure can be manufactured by one continuous crystal growth on a substrate in which grooves have been formed, and since the formation of the grooves is relatively simple, this laser fabrication can be easily performed with good reproducibility.

By the way, for the laser excitation light λ = 0.78 μm in the first shallow groove region 51.52, the p-type Ga As
Since the substrate has an absorption loss of several thousand ci1 to 10,000 cm, the laser beam suffers a large absorption loss in the flat area outside the first shallow groove 51, 52. Most of the laser beam is absorbed into the active layer. It has become clear that a positive effective refractive index difference is generated in the first shallow groove portion simply by absorbing some of the light that leaks into the adjacent guide layer but leaks toward the substrate side and undergoes absorption loss. On the other hand, since the increase in gain in the primary transverse mode is suppressed by absorption loss outside the first shallow groove, fundamental transverse mode oscillation is maintained in large optical output oscillation.

Although this embodiment shows the case where there are two first shallow grooves, any number of excitation regions can be formed. Also,
Although an embodiment using a p-type substrate will be described, it is also possible to invert pn and use an n-type substrate. Furthermore, although this embodiment has been described with respect to the AtGaAs/GaAs double heterojunction crystal material, other than the AtGaAs/GaAs double heterojunction crystal material, for example, In
GaAsP/InGaP.

InGaAsP/InP, InGaP/AtGaP, A
It can be applied to many crystal materials such as 7GaAsSb/GaAs8b.

[Brief explanation of the drawing]

Figure 1 is a perspective view of an embodiment of the present invention, and Figure 2 is A of Figure 1.
- A sectional view taken at part A, Figure 3 is B in Figure 1, -
4 is a cross-sectional view taken along the line C--C in FIG. 1, and FIG. 5 is a perspective view of the substrate in FIG. 1. In the figure, 10... p-type Ga As
Substrate, 11...p-type At6.4Ga 0.6
A s cladding layer, 12... Undoped A t
6.15GaO,B5As active layer, 13...
- n-type Ato, 27 Ga O, 73 As guide layer, 14------- n-type A 16.4 Ga g,
6 A B cladding layer, 15...p-type G
a As cap layer, 16...SiO2 film,
17... Diffusion region in the first V groove region, 18.
...Diffusion region in the second V-groove region, 19...
...N-type ohmic contact, 2o...P-type ohmic contact, 51.52...Track first groove (region), 53°...Second groove (region), 54.・・・
... ■Groove, 55... Curved groove. JP-A-59-68988 (6) f) 4 Figure C

Claims (1)

[Claims] It has a plurality of first grooves parallel to each other in the central part in the longitudinal direction of the resonator, and has a second shallow groove in a part of the extension in the longitudinal direction of the resonator, and has internal reflections at both ends of the resonator. A semiconductor substrate having a deep groove formed near its surface, an active layer and a guide layer having a refractive index lower than that of the active layer on this semiconductor substrate, and a first layer having a refractive index lower than that of this guide layer. a multilayer structure sandwiched between second cladding layers, wherein the active regions of the plurality of first shallow trench regions and the active regions of the second shallow trench regions are provided on the same plane and separated from each other. , these first. A semiconductor laser characterized in that a step is provided between the active layer in the second shallow groove region and the active layer in the deep groove, and the active layer in the deep groove is made into a non-excitation region.