JP3127635B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a so-called surface-emitting type semiconductor laser for extracting, for example, output light from a semiconductor laser in a plane direction perpendicular to a substrate and a method of manufacturing the same.

[0002]

2. Description of the Related Art Semiconductor lasers are widely used as optical disks, light sources for optical fiber communication, etc., and are further improved in characteristics such as higher coherence and higher output, and are also monolithically integrated with functional devices such as optical modulators. Is being promoted. In particular, in recent years, realization of large-scale two-dimensional integration has been desired in consideration of application to parallel optical information processing in an optical computer or the like or large-capacity parallel optical transmission. However, it is extremely difficult to monolithically integrate a conventional semiconductor laser because performance tests cannot be performed without element isolation. On the other hand, as a semiconductor laser capable of two-dimensional integration, a surface emitting laser that emits a laser beam in a direction perpendicular to a substrate surface has attracted attention.

As such a surface emitting laser, for example, a mirror surface is formed at an angle of 45.degree. With respect to a substrate, facing a light emitting end surface of a normal semiconductor laser, and the laser light is reflected by the mirror surface so as to reflect the laser light to the substrate. A configuration for taking out in a direction perpendicular to the plane is adopted. In order to form such a surface emitting laser as a monolithic structure, RIE is generally used.
By using anisotropic dry etching such as (reactive ion etching), RIBE (reactive ion beam etching), or ion milling, for example, a semiconductor layer formed on a substrate can be removed from a direction perpendicular to the substrate. , 45
The laser light emitting end face and the mirror surface can be formed by performing anisotropic etching twice from an oblique direction of about °.

However, in the case of forming by such anisotropic dry etching, a considerable damage is caused on the etching interface, and it is difficult to form the end surface of the active layer and the mirror surface with flatness on the order of an atomic layer. In addition, when a highly reflective film is applied to the end face of the active layer, the application of the highly reflective film causes damage to the active layer, causing a change or deterioration in characteristics, and it is difficult to efficiently extract laser light in the plane direction.

For this reason, there has been proposed a configuration in which a semiconductor layer and a reflection surface are laminated on a substrate to form a resonator in a direction perpendicular to the substrate surface, and a laser beam is emitted in the vertical direction (for example, R.A. See, Applied Physics, Vol. 60, No. 1 (1991), pp. 2-13, by Gels et al. An example of this vertical cavity semiconductor laser will be described with reference to FIG.

In this case, an n-type distributed reflective multilayer film 13 doped with, for example, Si is formed on a semiconductor substrate 1 made of, for example, n-type GaAs. The distributed reflection type multilayer film 13 may have a configuration in which, for example, AlAs and GaAs are stacked for 28.5 periods. On top of this, for example, a thickness of 8 nm
The active layer 6 having a quantum well structure made of In _0.2 Ga _0.8 As or the like, and further, for example, a p-type distributed reflective multilayer film 14 doped with Be are formed. The p-type distributed reflection type multilayer film may have a configuration in which, for example, AlAs and GaAs are stacked for 28.5 periods. Further, a cap layer 15 made of GaAs or the like and having a thickness of 1/4 with respect to the wavelength of the oscillation light is applied thereon.

Each layer 1 has a predetermined width and length.
3, 6, 14 and 15 are patterned. That is, after a groove having a depth reaching the n-type distributed reflection type multilayer film 13 is formed by etching using photolithography or the like, the periphery is covered with a buried layer 16 made of polyimide or the like. An electrode 10 made of, for example, is deposited by sputtering or the like.
To reflect light oscillated from the active layer 6 by the p-type and n-type distributed reflection type multilayer films 13 and 14 as shown by the arrow L _O , and to form a resonator in the film thickness direction. Can be obtained.

In particular, when the reflector constituting the resonator is constituted by a pair of distributed reflection type multilayer films of p-type and n-type, it is necessary to obtain p-type conduction with low resistance because it includes a large number of hetero barriers. When a multilayer reflector is used for a current injection type laser, it is difficult to reduce the resistance.
It is conceivable to use a dielectric multilayer film as the distributed reflection type multilayer film. However, in this case, not only the manufacturing process becomes complicated, but also a problem that current injection becomes difficult occurs.

In the above structure, since the resonator is formed in the vertical direction, the length of the gain region is determined by the thickness of the active layer, and it is difficult to increase the gain region, and the gain obtained is small. Therefore, in order to achieve a sufficiently low threshold,
It is necessary that the distributed reflection type multilayer film has a high reflectance of about 95% or more. However, when the emission end face has a high reflectance as described above, the amount of emitted light to the outside is small, and consequently, there is a problem that it is difficult to apply the method to a high-output laser.

On the other hand, as a structure capable of obtaining a sufficiently high output, there is a structure in which a 45 ° reflecting mirror is formed near the end face of a normal horizontal cavity laser to obtain an output perpendicular to the substrate surface (for example, “LPLee et al.”). al.Appl.Phys.Lett.57 (1990) pp2048-
2050 "). Although this configuration is simple in principle, the end face of the resonator and the 45 ° external reflection mirror are generally manufactured by using an etching technique such as RIBE, so that the manufacturing process is complicated and the end face and the external reflection mirror are required. It is difficult to control the flatness and angle accuracy of the light emitting device, which may cause a shift in the output angle and aberration.

Further, as another structure capable of obtaining a sufficiently high output, a normal horizontal cavity type laser structure is manufactured, and then a 45 ° etching is performed without forming a vertical end face, and the oblique end face is entirely exposed. There has been reported an example in which a bent mirror is formed as a reflecting mirror (for example, "N. Hamao et al. Appl. Phys.
Lett. 54 (1989) pp. 2389-2391 ") However, since this structure is manufactured by using an etching technique such as RIBE similarly to the above-mentioned external reflector type, the same problem as in the above-described example occurs. The angular accuracy of the degree mirror becomes extremely difficult.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a surface emitting type semiconductor laser for extracting a laser beam in a direction perpendicular to the main surface of a substrate. And high output.

[0013]

FIG. 1 is a schematic enlarged cross-sectional view of an example of the present invention. As shown in FIG. 1, at least distributed reflection is provided on a semiconductor substrate 1 having a {100} crystal plane as a main surface 1S. Type multilayer film 3, first cladding layer 5, active layer 6,
The second cladding layer 7 is formed by lamination, and {110}, {101}, and {1-1} of the {110} crystal plane are formed above each layer.
Slope 9 surrounded by crystal planes of {0} and {10-1}
A, 9B} are provided as reflecting mirrors.

FIG. 2 is a schematic enlarged sectional view of an example of the present invention. As shown in FIG. 2, at least a distributed reflection type multilayer film 3 is formed on a semiconductor substrate 1 having a {100} crystal plane as a main surface 1S.
And the first cladding layer 5 is formed thereon, and
{110}, {101}, {1-10},
Slope 9A, 9 surrounded by each crystal plane of {10-1}
B ‥‥ is formed as a reflecting mirror, and the slopes 9A, 9B ‥‥
, At least the active layer 6 and the second cladding layer 7 are provided in a region surrounded by.

Further, according to the present invention, in each of the above-mentioned lasers, the distributed reflection type multilayer film 3 is formed as an n-type. In addition, the present invention provides a method as described above, wherein each of the above-described lasers has a slope 9A, 9B #.
The longest side of the bottom surface of the region surrounded by is set to 10 μm or less.

[0016]

As described above, in the present invention, as shown in FIG. 1, at least the distributed reflection type multilayer film 3 and the first cladding layer 5 constituting the laser are formed on the {100} main surface 1S of the semiconductor substrate 1, A layer 6 and a second cladding layer 7 are formed,
On top of this, four slopes 9A and 9 made of {110} crystal planes
B ‥‥ is configured as a reflecting mirror, and the oscillation light of the active layer 6 is transmitted between the reflecting mirror and the distributed reflection type multilayer film 3 by arrows a
b and arrow d, is reflected as indicated by e and a resonator in a thickness direction of the semiconductor layer, the substrate as indicated by an arrow L _O 1
Oscillating light can be emitted to the back side of the substrate.

Such a {110} crystal plane is formed by forming a mesa projection or a growth inhibiting layer having a side along the <001> crystal axis direction on a semiconductor substrate, and performing MOCVD (chemical vapor deposition using an organic metal). It is obtained spontaneously by growing a semiconductor layer by an epitaxial growth method such as that described above.

That is, Japanese Patent Application No. Hei.
As described in the -262259 application, the <00
1> When a {110} crystal plane is generated from a mesa protrusion extending in the crystal axis direction or a side portion of the growth inhibition layer, the {11}
Since the epitaxial growth rate is extremely slow on the 0 crystal plane, the growth side surface of the semiconductor layer is restricted by the {110} crystal plane and grows. By growing this slope until the four slopes intersect, a quadrangular pyramid-shaped 45 ° reflecting mirror can be formed with high accuracy, and the light from the active layer 6 can be efficiently reflected. it can.

According to the present invention, as shown in FIG. 2, at least a distributed reflection type multilayer film 3 and a first cladding layer 5 are formed on a {100} main surface 1S of a semiconductor substrate 1, and Active layer 6 in a region surrounded by {110} crystal planes of
Is provided, the side surface of the active layer 6 is regulated by the naturally generated slopes 9A and 9B #, and the oscillation light is reflected toward the base 1 by the slopes, and arrows c and d in FIG. And e, a so-called downward U-shaped bent resonator is formed, and the base 1 is formed as shown by an arrow L _O.
Laser light can be emitted to the back side of the.

Also in this case, a quadrangular pyramid-shaped 45 ° reflecting mirror can be formed with high precision by growing until the slopes intersect, and the light reflected upward from the distributed reflection type multilayer film 3 can be efficiently reflected. It can reflect well.

Further, when an active layer is provided in a region surrounded by the slopes 9A and 9B #, especially the side surface of the active layer is formed by RI.
Since the structure can be formed without applying dry etching such as E, the active layer can be prevented from being damaged, and an accurate 45 ° mirror surface can be obtained.

According to the present invention, since the resonator is formed in the film thickness direction, the distributed reflection type multilayer film 3 is
The resonator can be constituted only by providing between the semiconductor substrate 1 and the semiconductor substrate 1. That is, by configuring the distributed reflection type multilayer film 3 as n-type, it is possible to avoid an increase in resistance due to the p-type distributed reflection type multilayer film, and to lower the threshold value.

Furthermore, in the present invention, the slope 9
A, 9B}, the longest side of the bottom of the area surrounded by
By setting the thickness to 0 μm or less, the absorption of the oscillation light in this region is suppressed, the loss is reduced, and the laser light can be emitted to the back surface side of the base 1 with higher output.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the semiconductor laser of the present invention will be described below in detail with reference to the drawings. In each example, a case is shown in which n-type GaAs is used as the material of the semiconductor 1 and an n-type distributed reflective multilayer film 3 is provided thereon.

Example 1 In this case, as shown in FIG.
On a main surface 1S composed of, for example, a (100) crystal plane, n-type AlAs and GaAs doped with, for example, Si are provided.
A distributed reflection type multilayer film 3 in which s is alternately laminated at a period of 28.5 is formed by MOCVD or the like. Further on this, n
A first cladding layer 5 made of Al _0.2 Ga _0.8 As or the like, an active layer 6 of a quantum well structure made of In _0.2 Ga _0.8 As or the like having a thickness of 8 nm, a p-type Al _0.2 Ga _0.8
The second cladding layer 7 made of As
The epitaxial growth is performed by the method described above.

Then, the mesa projection 20 composed of each of the layers 3 to 7 is etched by applying photolithography or the like. In this case, a groove having a depth reaching an intermediate position of the thickness of the distributed reflection type multilayer film 3 is formed by anisotropic etching such as RIE, and each side surface of the mesa projection 20 has a <001> crystal indicated by arrows x and y. Patterning is performed, for example, in a plane square shape so as to be a plane along the axial direction, <0-10> crystal axis direction.

Next, a high-reflection protective film 4 is formed on each side surface of the mesa projection 20 by patterning so that its upper part protrudes from the upper surface of the second cladding layer 7. This patterning is performed, for example, by forming the second clad layer 7 on the second clad layer 7.
After forming a semiconductor layer having etching selectivity, patterning for forming the mesa protrusion 20 is performed, and a high-reflection protective layer is further entirely deposited by vapor phase growth or the like, and then anisotropically, such as RIE, is entirely deposited. Etching is performed, and the mesa protrusion 20
The upper semiconductor layer is removed by etching to form the second clad layer 7.
Can be formed by exposing them.

Further, a semiconductor layer 8 of p-type Al _0.3 Ga _0.7 As or the like is epitaxially grown thereon by MOCVD or the like. At this time, the growth condition is normal pressure or reduced pressure, for example, normal pressure MOCVD, and the growth rate is 0.4 n.
m / s or less, V / III ratio of 200 or more, growth temperature of 800
℃ or more, for example, trimethylgallium (TMG),
It is formed of a methyl-based material such as trimethylaluminum (TMA).

The side portions 21A and 21B where the upper surface and the side surface of the mesa projection 20 intersect are sides along the <001> crystal axis direction, and once {110} from the side portions 21A and 21B}.
When the crystal plane grows, the epitaxial growth rate is extremely slow on this {110} crystal plane, so that semiconductor layer 8 has slopes 9A, 9B composed of this {110} crystal plane.
Grow while composing.

FIG. 3 is a schematic enlarged plan view of the mesa projection 20. In FIG. 3, arrow x is the <001> crystal axis direction, arrow y is the <0-10> crystal axis direction, and arrow z is the base 1
Shows the <100> crystal axis direction orthogonal to the main surface 1S. In this case, the length Lt of each side of the mesa protrusion 20 is formed to be 10 μm or less, for example, 5 μm. The slopes 9A, 9B, 9C and 9D extending from each side are respectively (110),
Each of the crystal planes (1-10), (101), and (10-1) is epitaxially grown until each of the slopes 9A to 9D intersect to form a quadrangular pyramid-shaped reflecting mirror.

Further, as shown in FIG. 1, electrodes 10 and 11 are attached to the top of a quadrangular pyramid surrounded by each of the slopes 9A to 9D and the back side of the base 1, thereby obtaining a semiconductor laser according to the present invention. be able to. In this case, as the electrode material, for example, AlGaAs or GaAs forming the semiconductor layer 8 and a material forming an ohmic electrode such as Ti / Pt / Au are used.
Can be used. The shape is, for example, a slope 9A to obtain a high reflectance at a portion where the oscillation light is reflected.
For example, a pattern is formed in a substantially hollow rectangular space pattern so as to cover only the lower side of 9B #. In this case, in a portion where the electrode 10 is not attached, a relatively high reflectance can be obtained due to a difference in refractive index between the semiconductor layer and air. For example, in the case of GaAs and air, a relatively large refractive index difference of about 3.62: 1 can be obtained, and a sufficient reflectance as a reflecting mirror can be obtained.

With this configuration, the oscillating light from the active layer 6 can be accurately reflected vertically downward as shown by arrows a and b. As shown by (e) and (e), light is reflected upward, and a vertical resonator in the film thickness direction can be formed by the reflecting mirror formed by the slopes 9A and 9B and the distributed reflection type multilayer film 3. In this case, the reflecting mirror is formed with high accuracy because it is constituted by a naturally occurring crystal plane.
The outgoing light can be emitted with high output as shown by the arrow L _O on the back side of the light emitting element.

In this case, the n-type distributed reflection type multilayer film 3
Since only a resonator can be configured,
It is possible to avoid the increase in resistance due to the p-type distributed reflection type multilayer film and reduce the threshold value. Furthermore, by setting the length of the bottom side of the region constituting the reflecting mirror to 10 μm or less, loss of light output can be suppressed.

Embodiment 2 Next, another embodiment of the present invention will be described in detail with reference to FIG. In this case, for example, an n-type GaAs buffer layer 2 and an n-type distributed reflection type multilayer film 3 are epitaxially grown on a semiconductor substrate 1 made of n-type GaAs or the like by MOCVD or the like. The mesa protrusion 20 is formed by a method. Also in this case, arrows x and y
Are formed in a substantially square shape having side surfaces extending in the <001> crystal axis direction and the <0-10> crystal axis direction, and the length of each side is 10 μm or less, for example, 10 μm.

After the high reflection protective film 4 is formed around the mesa projection 20 by the same forming method as in the first embodiment, a first cladding layer made of n-type Al _0.2 Ga _0.8 As or the like is formed. 5, for example, 8 nm thick In _0.2 Ga
Active layer 6 of quantum well structure made of _0.8 As or the like, p-type A
A second cladding layer 7 of l _0.2 Ga _0.8 As or the like, and a semiconductor layer 8 of p-type GaAs or the like are epitaxially grown.

At this time, the growth conditions are set to the values in the first embodiment.
The growth rate is 0.4 nm or less and the V / III ratio is 200
As described above, when the growth temperature is set to 800 ° C. or more and the layers are formed by normal pressure or reduced pressure, for example, normal pressure MOCVD or the like, each layer grows while forming the slopes 9A and 9B composed of {110} crystal planes. The growth is performed until 9A, 9B} intersect to form a quadrangular pyramid-shaped reflecting mirror.

Then, the electrodes 10 and 11 are applied to the top of the cap layer 8 and the back side of the substrate 1 to obtain the semiconductor laser according to the present invention. In this case, for example, Ti / Pt / Au can be used as the electrode material in the same manner as in the first embodiment, and the shape thereof is such that the oscillating light from the active layer 6 has high reflectivity on the slopes 9A and 9B #. It is formed so as to be reflected. That is, in this case, only the top is adhered.

With such a configuration, the oscillating light in the active layer indicated by the arrow c is reflected downward by the end surface of the active layer 6 regulated by the slopes 9A and 9B, and the distributed reflection type multilayer film 3 is used. Light is reflected upward as indicated by arrows d and e, and further reflected downward by a reflecting mirror formed by the inclined surfaces 9A and 9B. A vertical resonator can be configured.

Also in this case, since the reflecting mirror is constituted by a crystal plane which grows spontaneously, it can be formed with high precision, can emit a laser beam with high output, and has an n-type distributed reflection type. Since the resonator can be constituted only by the multilayer film 3, it is possible to avoid the increase in resistance by the p-type distributed reflection type multilayer film. Furthermore,
By setting the length of the base of the region constituting the reflecting mirror to 10 μm or less, loss of light output can be suppressed.

Further, in this case, since the active layer 6 is provided in a region surrounded by the slopes 9A and 9B #, the end face of the active layer 6 is spontaneously generated without being processed by etching such as RIE. , And a laser having good crystallinity can be formed.

Embodiment 3 Next, another embodiment of the present invention will be described in detail with reference to FIG. 3, parts corresponding to those in FIGS. 1 and 2 are denoted by the same reference numerals, and redundant description will be omitted.

In this example, a distributed reflection type multilayer film 3, an n-type first cladding layer 5, and an active layer 6 are formed on a semiconductor substrate 1.
After the epitaxial growth of the p-type second cladding layer 7, impurities are implanted so as to regulate the region constituting the resonator to form a diffusion region 23, and thereafter, a growth blocking layer 24 made of a dielectric or the like is formed. Is formed as a pattern having an inner surface extending in the <001> crystal axis and <0-10> crystal axis directions indicated by arrows x and y, in particular, the length of each side surface is 10 μm or less, for example, 10 μm. Then, a cap layer 8 made of GaAs or the like is further epitaxially grown thereon under the same growth conditions as those of the above-described first and second embodiments, and the slopes 9A, 9 made of {110} crystal planes are formed.
A quadrangular pyramid-shaped reflecting mirror constituted by B ‥‥ is formed.

Then, as shown by arrows a and b, the laser beam is reflected by the reflecting mirror.
Thus, information can be reflected as indicated by arrows d and e to form a resonator, and laser light can be emitted from the back surface of the base 1 as indicated by an arrow L _O.

Also in this case, the vertical resonator can be constituted by a reflecting mirror made of a crystal plane, so that a laser beam can be emitted with high output, and the resonator is formed only by the n-type distributed reflection type multilayer film 3. , It is possible to avoid an increase in resistance due to the p-type distributed reflection type multilayer film. Furthermore, by setting the length of the bottom side of the region constituting the reflecting mirror to 10 μm or less, loss of light output can be suppressed.

In each of the above examples, a GaAs-based semiconductor substrate is used, and an AlGaAs-based distributed reflection multilayer film, a cladding layer, and an InGaAs-based active layer are provided thereon. InP-based, GaAlIn
The present invention can be applied to various compound semiconductor lasers such as As-based and InGaAsP-based, and it goes without saying that various modifications and changes other than the above-described embodiments are possible in the configuration.

[0046]

As described above, according to the present invention, a vertical cavity surface emitting laser can be formed with high accuracy, and high output can be achieved.

Further, by forming the active layer in the region constituting the reflecting mirror, epitaxial growth can be performed with good crystallinity.

Further, since the resonator can be formed without forming the p-type distributed reflection type multilayer film, it is possible to avoid the increase in the resistance due to the p-type distributed reflection type multilayer film, thereby reducing the threshold value. be able to.

Further, by setting the length of the base of the region constituting the reflecting mirror to 10 μm or less, the loss of the optical output can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged cross-sectional view of a first embodiment of the present invention.

FIG. 2 is a schematic enlarged cross-sectional view of a second embodiment of the present invention.

FIG. 3 is a schematic enlarged plan view of a main part of each embodiment of the present invention.

FIG. 4 is an enlarged schematic sectional view of a third embodiment of the present invention.

FIG. 5 is a schematic enlarged sectional view of an example of a conventional semiconductor laser.

DESCRIPTION OF SYMBOLS 1 semiconductor substrate 2 buffer layer 3 distributed reflection type multilayer film 4 high reflection protective film 5 first clad layer 6 active layer 7 second clad layer 8 semiconductor layer 9A slope 9B slope 9C slope 9D slope 20 mesa Protrusion

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-61187 (JP, A) JP-A-4-296082 (JP, A) JP-A-4-216691 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01S 5/00-5/50

Claims (4)

(57) [Claims] At least a distributed reflection multilayer film, a first clad layer, an active layer, and a second clad layer are formed on a semiconductor substrate having a {100} crystal plane as a principal surface, The {110} crystal planes {110} and {1}
A semiconductor laser characterized in that a slope surrounded by each crystal plane of {01}, {1-10} and {10-1} is provided as a reflecting mirror. 2. At least a distributed reflection multilayer film and a first cladding layer are formed on a semiconductor substrate having a {100} crystal plane as a main surface, and a {110} crystal plane of {110} is formed thereon. {101},
A slope surrounded by each crystal plane of {1-10} and {10-1} is formed as a reflector, and at least an active layer and a second cladding layer are provided in a region surrounded by the slope. A semiconductor laser characterized by the above-mentioned. 3. The semiconductor laser according to claim 1, wherein said distributed reflection type multilayer film is an n-type. 4. The semiconductor laser according to claim 1, wherein the longest side of the bottom surface of the region surrounded by the slope is 10 μm.
m or less.