JPH042189A - Surface emitting semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a surface emitting semiconductor laser having multiple stages of emitting functions in a direction perpendicular to the laminated surface of a semiconductor layer by so constructing that the end face of a first double hetero structure and the end face of a second double hetero structure formed thereon through an insulting layer have oblique surfaces of 45 degrees in a longitudinal direction of a resonator. CONSTITUTION:A window is opened in parallel with an end face over 50mum from an end face on which a first clad layer 14 to fourth clad layer 22 are grown by using a photoresist method, and so dry etched that the upper part of the end face is pushed out obliquely at 45 degrees to the longitudinal direction of a resonator. When the dry etching is executed in depth until the surface of a high resistance layer 17 is exposed, a second oblique surface 23 in which a light oscillated by a second active layer 21 is reflected perpendicularly, is formed. Then, the entire surface is covered with a resist film, and the same end face side is so dry etched that the layer 17 is arrived at a substrate in a pushing direction obliquely at 45 degrees to the longitudinal direction of the resonator. Thus, a first oblique surface 24 in which the light oscillated in a first active layer 15 is reflected perpendicularly, is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface emitting semiconductor laser used as a light source for optical switch elements, optical logic operation elements, etc. in the field of optical information processing.

[Conventional technology]

Surface-emitting devices that emit light in a direction perpendicular to the plane are used as light sources for devices with functions such as high-speed optical switches, optical logic operations, and optical image processing, and are used as basic devices such as optical information processing devices and optical computers. It has attracted wide attention as an optical functional device, and research and development is currently underway. This surface-emitting semiconductor laser has a structure with a cavity in a direction perpendicular to the laminated surface of the semiconductor layers, and a secondary grating that emits part of the light traveling in the longitudinal direction of the cavity in the vertical direction. There is a structure. Further, unlike this, there is a semiconductor laser having a structure in which a 45-degree reflecting mirror is provided on the extension of the resonator in the longitudinal direction. This semiconductor laser was developed by Liau (Z, L, Liau) and Walpole (J, N, Walpole) as an effective semiconductor laser with a simpler structure and manufacturing method than a semiconductor laser provided with a grating.
Physics Letter (Applied Physics
Letters) 1985 Volume 46 N [Li2115
Published on pages 117 to 117. This semiconductor laser has a striped laser resonator 101 as shown in FIG.
A 45-degree reflective surface 102 is formed on the extension of the resonator, and the light emitted from the resonator is reflected in the vertical direction by the 45-degree reflective surface.

[Problem to be solved by the invention]

Surface-emitting semiconductor lasers with a vertical cavity structure or a secondary grating structure have extremely complex structures. There is a risk that laser oscillation may not occur.

Further, the structure using a 45-degree mirror has the disadvantage that a clear light emission pattern cannot be obtained and reproducibility is impaired.

Furthermore, all of the above-mentioned elements are single units or prototypes within a single plane, and multi-stage integration in a direction perpendicular to the laminated plane of semiconductor layers, which is important for optical integrated circuits, has not yet been proposed. Furthermore, when performing optical information processing by combining surface-emitting devices, it is necessary to have an element structure that not only emits light from the surface but also responds to light injected from a direction perpendicular to the stacked surface of the semiconductor layers.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, stably and efficiently emit light in the vertical direction, and provide a multi-stage emission function in the direction perpendicular to the laminated surface of semiconductor layers. An object of the present invention is to provide a surface-emitting semiconductor laser that reacts even to light injected from a direction perpendicular to the surface.

[Means to solve the problem]

A first means provided by the present invention to solve the above-mentioned problems is a striped carrier injection method that has a convex stripe region on the surface and covers a part of the upper surface of the stripe region of the convex stripe region. A first active layer is formed on a semiconductor substrate having a current blocking layer on a region other than the convex stripe region (i.e., the side surfaces of the convex stripe region) and on a flat surface on both sides of the convex stripe region. A striped first double heterostructure sandwiched between first and second cladding layers made of a material with a wider band gap than the first double heterostructure is provided in the longitudinal direction of the resonator, including at least one end surface, and A stripe-shaped insulating layer is provided adjacent to the double heterostructure of No. 1, and the second active layer is sandwiched between third and fourth cladding layers made of a material with a wider band gap than the second active layer. A second double heterostructure is provided adjacent to the insulating layer and stacked on at least a portion of the first double heterostructure, and the second double heterostructure is also provided in the striped carrier injection region. In the adjacent state, the end face of the first double heterostructure and the end face of the second duffle heterostructure stacked on the first double heterostructure form the convex stripe in the longitudinal direction of the resonator. This is a surface-emitting semiconductor laser characterized by having a 45-degree slope cut into the longitudinal direction of the resonator with respect to the upper surface of the region.

A second means of the present invention is a surface emitting semiconductor laser characterized in that the convex stripe region in the first means is replaced with a concave stripe region.

A third means of the present invention is a surface emitting semiconductor according to the first means or the second means, characterized in that the first active layer and the second active layer have different band gaps and oscillate at different wavelengths. It's a laser.

A fourth means of the present invention is that in the third means of the present invention, the first active layer and the portion of the second active layer adjacent to the striped carrier injection region are arranged in the longitudinal direction of the resonator. A region adjacent to the substrate, which is located on the extension thereof and includes at least a part of the portion of the first active layer adjacent to the striped carrier injection region, is perpendicular to the stacked surface of the semiconductor layer. The surface emitting semiconductor laser is characterized in that a hole is made in the substrate until the surface of the first cladding layer is exposed.

〔Example〕

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a perspective view of the first embodiment of the present invention, FIG.
The figures are AA' and BB' cross-sectional views of FIG. 1, respectively.
FIG. 4 is a perspective view of the second embodiment of the present invention, FIG. 5 is a sectional view in the longitudinal direction of the resonator of the third embodiment of the present invention, and FIG. 6 is a diagram of the fourth embodiment of the present invention. FIG. 3 is a cross-sectional view in the longitudinal direction of the resonator of the embodiment.

As shown in FIG. 7, a p-type GaAs substrate 101
A 5iCh film 11 is provided on top, and a 5iOz film is left in the form of a stripe of 3 μm in width in the longitudinal direction of the resonator using a photoresist method, and a window is formed outside the film and etched to a depth of 1.0 μm. After that, use the 5if2 film 11 as a diffusion mask.
A type impurity S (sulfur) is diffused to a depth of 0.5 μm. At this time, the convex region 12 has a depth of 0 from the side surface.
．． After being diffused by 5 μm, the convex top surface of about 2 μm remains as p-type GaAs in a stripe shape, and this region becomes a stripe-shaped carrier injection region 12. S (sulfur) is also diffused to a depth of 0.5 μm in the etched planar area outside the convex area, converting both sides of the convex area and the entire planar area outside thereof into n-type, and these areas are covered with a current blocking layer. 13
becomes. Next, after removing the 5i02 film 11, the n-type A I2
0.45 Ga o, ss A s first cladding layer 1
4 to 0.8 μm, undoped A Ilo, + Ga
G, 9As first active layer 15 of 0.06 μm, n-type AA'
o4sG EL o, ss A S second cladding layer 16
0.8 μm, Fe-doped A II O, 45G ao
, ss A S high resistance layer 17 with a thickness of 0.2 μm M OV
Continuous growth using PE method.

In the above growth, the MOVPE method is a vapor phase growth method using an organic metal, so by changing the composition of the mixed gas, layers of any composition can be easily grown into any multilayer structure. Growth can be well controlled. Furthermore, in the MOVPE method, particles of each composition grow while bonding, so when multilayer growth is performed on a substrate with a convex shape as in the structure of the present invention, in the convex region, the particles of different compositions grow in a manner that follows the shape of the convex part. A thick layer grows.

Next, each grown layer is etched using a photoresist method on the growth surface to leave a resist film of 250 μm from the end face of the resonator and to open a window parallel to the end face. The above etching can be easily carried out using a phosphoric acid-based etching solution. After the surface of the substrate having convex regions is roughened by etching, the surface is etched with a mixed solution of ammonia solution and hydrogen peroxide solution. With this mixed solution, GaAs is etched, but with AρGaAs, the surface is oxidized and is not etched. At this time, care must be taken to avoid etching the current blocking layer 13 converted to n-type in the GaAs substrate. In this way, a high resistance layer 17 is formed on the surface of the grown layer, and each oxidized AρGaA layer 17 is formed on the etched side surface of the grown layer.
A growth layer is formed and the entire surface of the growth layer is electrically insulated (AAGaAs oxidized side surface 18).

Next, after removing the resist film, AρGaAs and GaAs are grown alternately in several layers to form a superlattice film 19. This superlattice film can be made into a film that totally reflects laser light by adjusting the composition and film thickness. This is followed by p
Type A 40.45 Ga o, 5sAs third cladding layer 20 1.0 μm, undoped A 12 a, + G
IL 0.9 A S second active layer 21 is 0.04 μm
The n-type A no, ss Ga o, and ss AS fourth cladding layers 22 are successively grown to a thickness of 1.0 μm using the MOVPE method. These growth layers grow on the substrate with convex regions and along the high resistance layer 17 and the oxidized Aj7GaAs growth flanks 18.

Next, using a photoresist method, a window is opened parallel to the end face over a distance of 50 μm from the end face where the first cladding layer 14 to the fourth cladding layer 22 have been grown, and the upper part of the end face protrudes at an angle of 45 degrees with respect to the longitudinal direction of the resonator. Dry etching into the desired shape. At this time, the resist film serves as an etching mask. Further, when performing dry etching, it is preferable to tilt the substrate at 45 degrees with respect to the vertical dry etching beam. If the dry etching is performed to a depth such that the surface of the high-resistance layer 17 is exposed, a second slope 23 is formed on which the light oscillated by the second active layer 21 is reflected in the vertical direction.

Next, the entire surface is covered with a resist film, and the same end face side as described above is dry etched in the direction in which the high resistance layer 17 protrudes at an angle of 45 degrees with respect to the longitudinal direction of the resonator until it reaches the substrate. In this way, a first slope 24 is formed on which the light oscillated by the first active layer 15 is reflected in the vertical direction.

Next, a groove is made in the high resistance layer 17 up to the second cladding layer 16,
A first n-type ohmic contact 25 is formed in this groove. Further, by attaching a second n-type ohmic contact 26 to the surface of the fourth cladding layer 21 and attaching a p-type ohmic contact 27 to the p-type GaAs substrate 10, a surface emitting semiconductor laser according to the first embodiment of the present invention can be obtained. (Figure 1, Figure 2, Figure 3).

A concave region is formed on the substrate in place of the convex region formed on the substrate in the first embodiment. At this time, as shown in FIG. 8, an n-type GaAs layer is formed on the p-type GaAs substrate 10, and striped grooves are formed in the n-type GaAs layer in the longitudinal direction of the resonator to a depth that reaches the p-type GaAs substrate 10. Form. This n-type GaAs layer becomes the current blocking layer 13,
The current blocking effect is larger and more effective than in the first embodiment. The surface emitting semiconductor laser of the second embodiment of the present invention can be obtained by manufacturing the other components in the same manner as the first embodiment (FIG. 4).
.

In the first and second embodiments, the first active layer 15 is undoped A (la, + s Ga o, s s
When the As first active layer 28 is used, a surface emitting semiconductor laser according to the third embodiment of the present invention is obtained (FIG. 5). This third
In this embodiment, the growth layer thickness of the third cladding layer 19 is adjusted so that the first active layer 28 on the striped carrier injection region 12 and the second active layer grown on the substrate having a convex region or a concave region are formed. 21, the portion adjacent to the striped carrier injection region is placed in the same plane in the longitudinal direction of the resonator. Next, a resist film is formed from a part of the first active layer 28 grown on the substrate having a convex region or a concave region, at a point perpendicular to the substrate, which is located above the striped carrier injection region 12. By using dry etching and chemical etching as a protective film, a hole 29 is bored in the substrate IO until the surface of the first cladding layer 14 is exposed, thereby obtaining a surface emitting semiconductor laser according to a fourth embodiment of the present invention.

At this time, the superlattice reflective film 19 is designed to reflect 50% of the laser beam from the first active layer 28 (FIG. 6).

[Effect]

When a voltage is applied between the first n-type ohmic contact 25 and the p-type ohmic contact 27 on the substrate 10, the following operation occurs.

In the structure of the present invention, the surface of the p-type substrate 10 except for the central portion of the convex top surface is the current blocking layer 13, so that the current injected from the p-type substrate side is transmitted to the central portion of the convex top surface. through only the carrier injection region 12 of the first
It is implanted into the cladding layer 14 and into the first active layer 15 adjacent to this layer. At this time, carriers are injected into the portion of the first active layer 15 located above the convex shape. The carriers injected into the active layer diffuse in the horizontal and lateral directions of the active layer, form a gain distribution centered on the portion located above the convex region, and start laser oscillation.

In particular, in the structure of the present invention, as shown in FIG. 3, the active layer in the convex portion that becomes the active region in the horizontal direction of the active layer is sandwiched between the second crat layers 16. Therefore, light in the active layer is focused on the active region having a high refractive index in the horizontal direction of the active layer, and is mode-controlled by a positive refractive index queiding mechanism based on a positive refractive index distribution. Therefore, stable fundamental transverse mode oscillation can be maintained.

In the above laser oscillation, one of the lights emitted from the active region of the first active layer 15 in the longitudinal direction of the cavity is A I2
The superlattice reflective film 19 passes through the G a As oxidized side surface 18
reaches and is totally reflected. The totally reflected light passes through the active region and travels in the direction of the first slope 24, is reflected at right angles from the first slope 24, and travels in the vertical direction. In this way, when it reaches the high resistance layer 17, part of it is emitted and the other part is reflected and returns in the opposite direction. Finally, a resonator is formed between the high resistance layer 17 and the superlattice reflective film 19, and laser oscillation occurs. occurs (dashed line in Figure 2).

In addition, the second n-type ohmic contact 26 and the substrate 10
When a voltage is applied between the upper p-type ohmic contact 27 and the upper p-type ohmic contact 27, an operation similar to that described above occurs in the second active layer 21. That is, the current injected from the p-type substrate 10 is injected from the third cladding layer 20 into the second active layer 21 through only the carrier injection region 12 at the center of the upper surface of the convex region. Then, a gain distribution is formed centered on the portion of the second active layer 21 located above the convex region, and laser oscillation is started.

The active layer located above the convex region serving as the active region is sandwiched between the fourth cladding layers 22 at both ends thereof. Therefore, light is focused on the active region with a high refractive index and mode-controlled by a positive refractive index guiding mechanism. Therefore, stable fundamental transverse mode oscillation can be maintained.

In the longitudinal direction of the resonator, light emitted from the active region travels through a portion of the second active layer 21 located above the convex region. As shown in FIG. 2, this active layer is curved, but since the active layer has a high refractive index and the curvature of the curve is small, light is condensed within the active layer and travels. second out of light
Those traveling toward the slope 23 are reflected at right angles by the second slope 23 and proceed vertically upward. and some are fourth
It is emitted from the cladding layer 22, and a part of it is reflected and returns to the original path to reach the resonator end facet, and a resonator is formed between the fourth cladding layer and the resonator end facet, and laser oscillation occurs.

Further, in the structure of the present invention, the first cladding layer 14.degree., the first active layer 15.degree. Since the area around the double heterostructure of the second cladding layer 16 is electrically insulated, the third cladding layer 20
．． Second active layer 21. They can be operated independently of the double heterostructure of the fourth cladding layer 22. It is also possible to use a lens to focus two oscillation lights that emit light from a surface and use them as intensity changes (both oscillate, one oscillate, and neither oscillate).Also, since the oscillation points are separated by 50 μm, each surface emits independently. It can also be used as a light source.

In the second structure of the present invention, the above-mentioned convex region is made into a concave region. It operates on the same principle as the first embodiment and has the same effect, but by making it concave, it has the following effect. First, when forming the current injection region in the concave region, as described in the embodiment, an n-type GaAs layer is grown on the p-type GaAs substrate 10, and then a striped groove is formed on the p-type GaAs substrate 10.
Open until you reach the aAs substrate. At this time, n-type Ga
The As layer becomes the current blocking layer 13, and the current blocking effect is greater than that in the first embodiment. Therefore, p-type Ga
Since the carriers injected from the As substrate IO more effectively enter the active layer and contribute to laser oscillation, lower threshold oscillation is possible than in the first embodiment.

Furthermore, in the case of this second structure, both ends of the active region of the first active layer 15 are sandwiched between the first cladding layers 14, and both sides of the second active layer 21 are sandwiched between the third cladding layers 20, each having a positive refractive index. Although the second active layer has a guiding mechanism, the width of both sides of the second active layer is such that in the region where it overlaps the first active layer 15, strip-shaped carriers formed apart from each other in the longitudinal direction of the resonator of the first active layer 15 are formed. It is narrower than the portion of the second active layer 21 adjacent to the implanted region. The second active layer 21 in this wide region becomes an active region, whereas when the laser oscillation light travels in the direction of the second slope 23, the second active layer acts as a narrow optical waveguide, so the second active layer 21 becomes an active region. The light reflected by the slope 23 and emitted vertically is concentrated. On the other hand, in the first embodiment, the width of the second active layer near the reflected region tends to become wider, and the light condensing property deteriorates.

In the third structure of the present invention, the first active layer 28 and the second active layer 21 have different laser oscillation wavelengths. Therefore, the first slope 24
The laser oscillation light that is bent at a right angle and emitted vertically has a wavelength of λ
1, whereas the wavelength of the laser oscillation light that is bent at a right angle at the second slope 23 and emitted vertically is λ2, making it a two-wavelength surface emitting laser.

In the fourth structure of the present invention, the first active layer 28 and the active region of the second active layer 21 are continuous in the stripe length direction, and further include a part of the active region of the first active layer 28. A hole 29 is placed in the vertical substrate. At this time, as in the embodiment, the band gap of the first active layer 28 (laser oscillation wavelength λ
1) is made wider than the bandgap (laser oscillation wavelength length 2) of the second active Jli 121. In this structure, the first active layer 28 and the second active layer 21 are excited just before each laser oscillates. In this state, a laser beam having a wavelength longer than λ is injected from the hole 29. The first active layer absorbs this light, and carriers in this region are excited, and as a result, laser oscillation is started by optical pumping. Of this laser oscillation light, A 12 G a A
50% of the light that passes through the s-oxide side surface 18 and reaches the superlattice reflective film 19 is reflected and retraces its original path, and the remaining light passes through and travels within the third cladding layer 20. Since there is a second active layer 21 with a high refractive index in the longitudinal direction of the resonator, the light is focused on this and travels. As a result, the second active layer 2
1 also starts laser oscillation using an optical pump. On the other hand, the wavelength λ of the laser injected light from the hole 29.

is λ. When λ1 is small, the first active layer does not absorb the injected light, so no optical pumping occurs and no laser oscillation occurs.

As described above, in the fourth embodiment, the first and second active layers are oscillated by optical pumping due to vertically injected light, and two wavelengths can be emitted in the vertical direction.

Generally, in optical logic circuits and the like which are important for optical information processing, a method of integrating optical functional elements and stacking them in multiple stages has been considered, and the present invention is a key element thereof.

〔Effect of the invention〕

The structure of the present invention does not simply emit surface light like the surface emitting laser prototyped by Liu et al., but has the following advantages.

(1) It has a structure in which two vertical laser oscillation light sources are stacked, and not only can it be used as an independent surface emitting light source, but if the two oscillation lights are focused with a lens, three types of intensity changes (double oscillation (1) One side oscillates (2) Both do not oscillate) Can be used as a light source.

(2) By changing the band gap between the two, it can be used as a two-wavelength surface emitting laser.

(3) Furthermore, by injecting laser light vertically through the hole, it is also possible to perform laser bombing on the laser oscillation region and emit two-wavelength plane light according to the injected laser light.

In addition, the example is AρG a As / G a A
Although double heterojunction crystal materials have been described, other crystal materials such as GaIgP/Aj2Ga IzMP.

The present invention can also be applied to semiconductor lasers made of many crystal materials such as GaAsP/lmGaP, IzGaAsP/lmGaP, and Aj2GaAsSb/GaAsSb.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the first embodiment of the present invention, FIG.
The figures are AA' and BB' cross-sectional views of FIG. 1, respectively.
FIG. 4 is a perspective view of a second embodiment of the present invention, FIG. 5 is a cross-sectional view in the longitudinal direction of the resonator of a third embodiment of the present invention, and FIG. 6 is a fourth embodiment of the present invention. Cross-sectional view in the longitudinal direction of the resonator, No. 7
The figure is a cross-sectional view when a current blocking layer is formed on the substrate in the manufacturing process of the first embodiment, and FIG. 8 is a schematic diagram of a conventional surface emitting laser. In the figure, 10...p-type GaAs substrate, 11...
5IO2 film, 12... Convex region, 13...
・・Current blocking layer, 14-- p-type A n Q, 45
G a a, ss A S first cladding layer, 15...
...Undoped A 42 olG a a, A s
First active layer, 16-・-n type A 120.450 a
os5A S second cladding layer, 17-Fe doped A
12 G, 45 Gao, ss As high resistance layer, 18...AAGaAs oxidized side surface, 19...
...Superlattice reflective film, 20...p-type A II O
, 450a a, 5sAs third cladding layer, 21...
... Undoped Apo, 1G ao, e As second active layer, 22- = -n type A 40.45G&o
, ss A S fourth cladding layer, 23... second slope, 24... first slope, 25...
1st n-type ohmic contact, 26...2nd
N-type ohmic contact, 27...P-type ohmic contact, 28...Undoped A n
o, +s G a o, ms A s first active layer, 2
9...hole, 101...laser resonator,
102... each shows a 45 degree reflective surface. Agent Patent Attorney Oto Uchihara 17-Superlattice reflective surface diagram No. 1? Figure No. 1 Wa - Super Ne each (te anti-shin 1゛Mako? 3... 2nd m1 curved area - No. 1'& No. 2

Claims (1)

[Scope of Claims] 1. On a semiconductor substrate having a convex stripe region on the surface and a current blocking layer on the side surfaces of the convex stripe region and the flat surfaces on both sides of the convex stripe region,
A striped first double heterostructure in which a first active layer is sandwiched between first and second cladding layers made of a material with a wider band gap than the first active layer is arranged in the longitudinal direction of the resonator. an insulating layer is provided adjacent to the first double heterostructure; A striped second double heterostructure sandwiched between fourth cladding layers is provided adjacent to the insulating layer and stacked on at least a portion of the first double heterostructure; The double heterostructure is also adjacent to the striped carrier injection region on the upper surface of the convex stripe region, and the end face of the first double heterostructure and the end face of a second double heterostructure stacked on the first double heterostructure. 1. A surface-emitting semiconductor laser characterized in that, in the longitudinal direction of the resonator, the surface-emitting semiconductor laser has a 45-degree slope cut into the upper surface of the convex stripe region in the longitudinal direction of the resonator. 2. A surface emitting semiconductor laser, characterized in that the convex stripe region of the surface emitting semiconductor laser according to claim 1 is replaced with a concave stripe region. 3. The surface emitting semiconductor laser according to claim 1 or 2, wherein the first active layer and the second active layer have different band gaps. 4. In the surface emitting semiconductor laser according to claim 3, a region of the second active layer adjacent to the striped carrier injection region is located on a longitudinal extension of the resonator of the first active layer. , the first active layer adjacent to the substrate so as to be perpendicular to the lamination plane of the semiconductor layer from a region including at least a part of the first active layer adjacent to the striped carrier injection region; A surface emitting semiconductor laser characterized in that a hole is bored in the substrate until the surface of the cladding layer is exposed.