JP2005243721A - Semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser device capable of light oscillation at a long-wavelength region in which the oscillation wavelength band is 1.3 μm or longer. <P>SOLUTION: When composing the SDH-type semiconductor device, an active layer 5 is composed of GaAsSb or GaAsSbN, thus composing the semiconductor laser device having an SDH-type semiconductor laser element capable of oscillation at a long-wavelength region without decreasing the smoothness of slopes 22, 23 by a crystal surface (111). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser device.

  As a semiconductor laser device, there is a semiconductor laser device having an SDH (Separated Double Heterostructure) type semiconductor laser element (for example, Patent Document 1 and Patent Document 2).

In this SDH type semiconductor laser device, a ridge having an upper surface with a predetermined crystal plane and extending in a predetermined crystal axis direction is formed on a semiconductor substrate, and a cladding layer extending from the ridge to the ridge groove, A semiconductor layer is formed by epitaxially growing a semiconductor layer such as an active layer, and forming a semiconductor stripe portion constituting a light emitting portion sandwiched by slopes of specific crystal planes on the ridge. In this semiconductor laser element, the above-described current blocking layer is formed by epitaxial growth on both sides of the semiconductor stripe portion.
Since the semiconductor laser element in this SDH type semiconductor laser device can accurately set the width of the laser resonator by the semiconductor stripe portion and match the positional relationship with the current blocking layer, it has a low threshold current and uniform optical characteristics. Characteristics.

FIG. 3 is a schematic cross-sectional view of a main part of the conventional SDH type semiconductor laser device.
This SDH type semiconductor laser device is usually applied to an AlGaAs type semiconductor laser, and <011> or <01 on one main surface of a (100) crystal plane of a GaAs substrate 102 of a first conductivity type (for example, n type). -1> A stripe-shaped ridge 102b having a required width along the crystal axis direction is formed. Then, the first conductivity type cladding layer 104, the active layer 105, the second conductivity type, for example, the p-type second conductivity type cladding layer 106, the current blocking layer 107, and the second conductivity layer on the upper layer are entirely covered so as to cover the ridge 102b. The mold cladding layer 108 and the second conductivity type cap layer 109 are formed by continuous epitaxy by MOCVD (Metal Organic Chemical Vapor Deposition).

In this configuration, the above-described semiconductor stripe portion 121 is formed on the ridge 102b by selecting the height, width, thickness of each semiconductor layer, and the like of the ridge 102b.
The semiconductor stripe portion 121 is formed by the step between the ridge 102b and the ridge grooves on both sides thereof, that is, depending on the height of the ridge 102b, the growth of the semiconductor layer is divided into the ridge 102b and the epitaxial growth in the ridge groove. By what is done.
At this time, the growth rate of the (111) B crystal plane and the (111) A crystal plane is particularly low compared to the growth rate of the top surface of the ridge 102b and the bottom surface in the ridge groove with respect to the (100) crystal plane. When the (111) B crystal plane or (111) A crystal plane is generated from the edge of the ridge extending in the <011> direction or the <01-1> direction, almost no growth occurs on these planes. Above, slopes 122 and 123 are formed by these crystal faces, and as a result, a semiconductor stripe part 121 sandwiched between these slopes 122 and 123 and having a fault between other parts is formed.

At this time, as described above, for example, the first conductivity type cladding layer 104 and the active layer 105 sandwiched between the slopes 122 and 123 by selecting the width and height of the ridge 102b, the thickness of each semiconductor layer, etc. The semiconductor stripe part 121 which comprises a laser light emission part by the 2nd conductivity type clad layer 106 is comprised.
On the other hand, in the ridge groove, each semiconductor layer on the ridge 102b, that is, the first conductivity type clad layer 104, the active layer 105, and the second conductivity type clad layer 106 is separated and simultaneously grown by epitaxial growth. A clad layer 104a, an active layer 105a, and a second conductivity type clad layer 106a are formed.
Then, the current blocking layer 107 is divided by the semiconductor stripe portion 121 and formed on both sides of the current blocking layer 107, and the upper second-conductivity-type cladding layer 108 and the cap layer 109 are entirely formed thereon. The semiconductor laser element, that is, the SDH type semiconductor laser device 101 having the same is configured.
Japanese Patent Laid-Open No. 61-183987 JP-A-6-77590

By the way, for example, the oscillation light in the long wavelength region of 1.3 μm band and 1.55 μm band is important because it is used as a light source of so-called optical access system and optical communication system. As a structure realized by a semiconductor laser device, a structure in which an InGaAsP-based laminated semiconductor layer is mainly formed on a substrate made of InP is used.
However, semiconductor laser devices using InGaAsP semiconductor laser elements have many problems such as weak electron confinement and low characteristic temperature.

In recent years, GaInNAs-based semiconductor laser devices, particularly semiconductor laser devices capable of optical oscillation in the 1.3 μm band, have been developed by using GaInNAs-based VCSEL (Vertical Cavity Surface Emitting Laser), which is a surface-emitting semiconductor laser device of an oxide constriction type. Has been.
However, in the semiconductor laser device of the GaInNAs system, it is difficult to grow the semiconductor layer by epitaxy in manufacturing, and in addition to the oxide layer of Al ₂ O ₃ used for current confinement and optical confinement, the semiconductor layer such as the GaInNAs active layer can be Since distortion due to a large lattice mismatch occurs, the reliability and the yield are problematic. Furthermore, since the oscillation light from such an oxide constriction type surface emitting semiconductor laser device includes light of different polarization planes TM (Transverse Magnetic) and TE (Transverse Electric), It is also extremely difficult to control the polarization plane.

Therefore, it is conceivable to obtain oscillation light in the above-mentioned long wavelength region with a GaInNAs-based SDH type semiconductor laser device. In the production of an SDH type semiconductor laser device, the temperature during crystal growth by epitaxial growth is increased. It is necessary to suppress crystal growth on the slope sandwiching the semiconductor stripe portion. However, the increase in the growth temperature makes it difficult to incorporate N into the crystal. In addition, when In coexists, this also inhibits the incorporation of N into the crystal in the production of an SDH type semiconductor laser device. End up.
That is, from the viewpoint of controlling the low threshold current and the polarization plane, a semiconductor laser device using an SDH type semiconductor laser element or the like which is a semiconductor laser element having a low threshold current is optimal. However, for the above reason, for example, conventional GaInNAs A problem in manufacturing occurs when a semiconductor laser device having a semiconductor laser element made of a system material is configured to perform light oscillation in a long wavelength region.

  An object of the present invention is to provide a long wavelength, low threshold semiconductor laser device suitable for use as a light source in an optical access system and an optical communication system.

  In the semiconductor laser device according to the present invention, a striped ridge is formed on the {100} crystal plane of a GaAs substrate, and at least a cladding layer, an active layer having GaAsSb, and a current block are formed on the main surface having the ridge. A semiconductor stripe portion formed by at least a clad layer and the active layer is formed in a cross-sectional triangular shape sandwiched by slopes of {111} crystal planes, and a semiconductor is formed along the slopes. And a semiconductor laser device in which a fault is formed between an active layer constituting a stripe portion and an active layer constituting another portion, and a current blocking layer is formed on both sides of the semiconductor stripe portion. Features.

In the semiconductor laser device described above, the active layer contains N (nitrogen).
In the semiconductor laser device described above, the active layer contains Al.
In the semiconductor laser device described above, the active layer has a multiple quantum well (MQW) structure.
According to the present invention, in the above-described semiconductor laser device, the crystal plane constituting the slope of the semiconductor stripe portion is a {111} B plane.
Further, the present invention is characterized in that a dimension of the semiconductor stripe portion in the longitudinal direction is 300 μm or more.
According to the present invention, in the above-described semiconductor laser device, the emission wavelength band varies depending on the selection of the width of the semiconductor stripe portion.

  As described above, in the semiconductor laser device according to the present invention, the semiconductor laser element constituting the semiconductor laser device is sandwiched between the {111} crystal planes, specifically the {111} B plane or the {111} A plane. A semiconductor stripe portion having a triangular cross section is formed, and a current path is limitedly formed in the semiconductor stripe portion of the semiconductor laser element by current blocking layers formed on both sides thereof.

In particular, in the present invention, the active layer constituting the semiconductor stripe portion of such a semiconductor laser device is made of GaAsSb, thereby controlling the oscillation wavelength band to a long wavelength band of 1.3 μm or more. It became possible to do.
In addition, the semiconductor laser device having an active layer made of GaAsSb has a characteristic temperature of about 80K, so that it can be made better than about 60K in an InP-based semiconductor laser device.
Furthermore, according to the semiconductor laser device of the present invention, the wavelength increase of the oscillation light is promoted by adding N to the active layer. Further, since the band gap ΔEc between the active layer and the cladding layer is increased, the characteristic temperature can be improved, and a semiconductor laser device having a characteristic temperature of, for example, about 120K to 150K can be configured.

Further, according to the semiconductor laser device of the present invention, since the slope sandwiching the semiconductor stripe portion is a {111} crystal face, for example, a {111} B crystal face, crystal growth on this slope is suppressed at the time of manufacturing the device. In the above, it is desirable to perform epitaxial growth at a high temperature. However, an increase in the growth temperature reduces the above-described introduction of N into the active layer.
However, according to the present invention, for example, by forming the active layer of the semiconductor laser device according to the present invention with Al, the introduction efficiency of N can be improved, so that the epitaxial growth temperature at the time of manufacturing the device can be increased. As a result, the crystallinity of the semiconductor stripe portion can be improved.

  As described above, the presence of In becomes a factor that inhibits the uptake of N. In the present invention, however, N can be taken in sufficiently and sufficiently by adopting a configuration that does not contain In. Even when N is introduced into the active layer for a longer wavelength, other elements constituting the active layer, such as Ga, As, and Sb, do not hinder the introduction of N into the crystal. The oscillation wavelength band can be easily controlled to the long wavelength region.

According to the semiconductor laser device of the present invention, the Al ₂ O ₃ oxidation constriction layer formed by the above-described oxidation of AlAs is not necessary, so that the semiconductor stripe portion and the current confinement layer constituting the device are made of only a material having high lattice matching. Therefore, the generation of crystal distortion is avoided, and the reliability and yield of the device are improved.
In the present invention, since the SDH type structure can be used, it is not necessary to perform epitaxial growth in a plurality of steps in the manufacture thereof. Therefore, the reliability and yield improvement by improving the lattice matching is achieved by the semiconductor. This is particularly important in laser devices.

  Further, in the semiconductor laser device according to the present invention, the main light emitting portion that becomes the gain region is limitedly narrowly formed. That is, the current confinement by the current blocking layer that defines the main current path for forming the light emitting portion and the light confinement based on this are sufficiently performed. Therefore, the occurrence of spatial hole burning is suppressed.

In the semiconductor laser device according to the present invention, when the current blocking layer is configured to face not only the active layer of the semiconductor stripe portion but also, for example, the second conductivity type cladding layer, the main current path in the semiconductor stripe portion described above. And the main light emitting portion in the active layer can be formed more limitedly.
Further, in the semiconductor laser device according to the present invention, when the current blocking layer is configured to face not only the active layer of the semiconductor stripe portion but also the first conductivity type cladding layer, for example, the main current path in the semiconductor stripe portion described above. And leakage of current from the semiconductor stripe portion to the other portion can be further suppressed.

Moreover, in the semiconductor laser device according to the present invention, the difficulty of polarization plane control in the surface emitting semiconductor laser device VCSEL described above is improved. For example, it becomes possible to oscillate light only by the TE polarization plane.
Thus, according to the configuration of the present invention, important and many effects can be brought about.

  In the following, an embodiment of an example of a semiconductor laser device according to the present invention will be described with reference to the drawings together with an example of a manufacturing method thereof for easy understanding.

First, an exemplary embodiment of a semiconductor laser device according to the present invention will be described with reference to the schematic sectional view of FIG.
FIG. 1 is a schematic cross-sectional view of a semiconductor laser element which is a main part of a semiconductor laser device 1 according to the present invention.
In this embodiment, a required width along the <011> or <01-1> crystal axis direction on one principal surface of the (100) crystal plane of the substrate 2 of the first conductivity type, for example, n-type GaAs. A stripe-shaped ridge 2b having the following is formed. Then, across the ridge 2b and the ridge grooves 2d on both sides of the ridge 2b, a buffer layer 3 of a first conductivity type, for example, GaAs, and a first conductivity type, for example, an n type Al _0.45 Ga _0.55 As, Conductive clad layer 4, active layer 5 having a quantum well structure of, for example, GaAsSbN and GaAs, for example, a multi quantum well (MQW) structure such as DQW (Double Quantum Well), and a second conductive type, for example, p-type The second conductive type cladding layer 6 made of Al _0.45 Ga _0.55 As is formed by, for example, continuous epitaxy using MOCVD (Metal Organic Chemical Vapor Deposition), thereby forming the semiconductor stripe portion 21.

At this time, a semiconductor having a triangular cross-section that constitutes the laser light emitting portion, which is composed of the first conductivity type cladding layer 4, the active layer 5, and the second conductivity type cladding layer 6 sandwiched between the inclined surfaces 22 and 23. A stripe portion 21 is formed.
On the other hand, in the ridge groove 2d, each semiconductor layer on the ridge 2b, that is, the first conductivity type cladding layer 4, the active layer 5, and the second conductivity type cladding layer 6 are separated from each other, and at the same time, the first conductive layer is formed by epitaxial growth. A mold cladding layer 4a, an active layer 5a, and a second conductivity type cladding layer 6a are formed.
On this, the current blocking layer 7 is divided by the semiconductor stripe portion 21 and formed on both sides thereof, and the second conductive type cladding layer 8 and the cap layer 9 which are the upper layers are formed on the entire surface. A semiconductor laser device having the semiconductor laser element according to the present invention is configured.
In this embodiment, the active layer 5 constituting the semiconductor stripe portion 21 and others along the inclined surfaces 22 and 23 by the (111) B crystal plane or the (111) A crystal plane defining the stripe portion 21 described above. A fault with the active layer 5a constituting the part is formed.

  Subsequently, an example of a method of manufacturing a semiconductor laser device according to the present invention will be described for each process with reference to the schematic cross-sectional views of FIGS. 2A to 2C.

  First, a base body 2 of a first conductivity type, for example, an n-type GaAs substrate having a (100) crystal face is prepared. 2A, at least a pair of parallel ridge grooves 2d is formed by wet etching on one principal surface composed of the (100) crystal plane of the substrate 2 along the <011> or <01-1> crystal axis direction. As shown, a ridge 2b having a required width having a ridge upper surface 2c made of a (100) crystal plane is formed between a pair of ridge grooves 2d.

Next, over the ridge 2b and the ridge groove 2d, that is, from the ridge top surface 2c to the ridge groove bottom surface 2e, a buffer layer 3 made of, for example, GaAs of the first conductivity type is formed to a thickness of 0.5 μm, for example, by epitaxial growth. To form.
After that, on the buffer layer 3, for example, a first conductivity type cladding layer 4 of 1 μm thickness made of Al _0.45 Ga _0.55 As of the first conductivity type, for example, GaAsSbN (thickness 0.01 μm) and GaAs (thickness). Active layer 5 having a multi quantum well (MQW) structure with a thickness of 0.02 μm and a second conductivity type with a thickness of 1 μm of a second conductivity type such as p-type Al _0.45 Ga _0.55 As. The cladding layer 6 is sequentially stacked and formed by epitaxial growth to form a semiconductor stripe portion 21 as shown in FIG. 2B.
In this configuration, the width of the active layer 5 is 1 μm, but the width is not limited to this. For example, suitable oscillation characteristics can be obtained in the range of 0.5 to 2 μm. It is also possible to form a guide layer having a thickness of 0.15 μm, for example, of GaAs between the active layer and each cladding layer.

The formation of the semiconductor stripe portion 21 on the ridge 2b is compared to the crystal growth rate in the <100> axis direction with respect to the upper surface 2c by the (100) crystal plane of the ridge 2b, compared with the (111) B crystal plane or the (111) A crystal. Since the crystal growth rate of the surface is slow, slopes 22 and 23 are formed by (111) crystal faces along the <011> or <01-1> crystal axis direction on both side edges of the ridge 2b, and the slopes collide with each other. At this stage, as shown in FIG. 2B, the triangular shape of the cross section of the semiconductor stripe portion 21 is completely formed.
In addition, when the above-mentioned (111) crystal plane is a (111) B crystal plane, since the new crystal growth from slope 22 and 23 is suppressed especially, by the smoothness improvement of slope 22 and 23, The shape of the semiconductor stripe portion 21 is defined with better reproducibility.

  That is, the slopes 22 and 23 formed by these crystal planes are formed by the semiconductor stripe portion 21 on the ridge 2b and the first conductivity type cladding layer 4a, the active layer 5a, and the second conductivity type cladding layer 6a on the other ridge groove 2d. A fault occurs between the semiconductor layer and these are separated.

In this way, after the top portion of the second conductivity type cladding layer 6 is completely formed by the inclined surface 22 and the inclined surface 23 to form the semiconductor stripe portion 21, subsequently, that is, by continuous epitaxial growth, for example, the first conductivity type Al A current blocking layer 7 having a thickness of 0.4 μm made of _0.45 Ga _0.55 As is formed to a thickness that does not cover the top of the second conductivity type cladding layer 6.
Thereafter, an upper second conductive type cladding layer 8 made of Al _0.45 Ga _0.55 As having a thickness of 1 μm, for example, is formed to cover the top of the second conductive type cladding layer 6, as shown in FIG. 2C. As shown, a cap layer 9 having a thickness of 500 nm made of, for example, second conductivity type GaAs is formed on the upper surface of the upper second conductivity type cladding layer 8 by, for example, epitaxial growth.

After the cap layer 9 is formed, the first electrode is deposited on the back surface of the substrate 2 by, for example, vapor deposition or sputtering, and the second electrode is deposited on the upper surface of the cap layer 9 by, for example, vapor deposition or sputtering. As a result, a semiconductor laser device 1 according to the present invention as shown in FIG. 1 is obtained.
When the active layer contains Al, if the amount of Al becomes too large, the oscillation wavelength will be shortened. Therefore, the Al ratio in the active layer is desirably 10% or less.

  Although the semiconductor laser device according to the present invention and the method for manufacturing the semiconductor laser device according to the embodiments have been described above, the semiconductor laser device according to the present invention and the method for manufacturing the semiconductor laser device are limited to the above-described embodiments. It goes without saying that it is not.

For example, in this embodiment, the first conductivity type is n-type and the second conductivity type is p-type, but both may be opposite conductivity types.
In this embodiment, the ridge has a reverse mesa shape, but this shape is not limited to the reverse mesa shape.

  In addition, when a semiconductor laser device is used for oscillation of communication laser light as a so-called optical access system light source, oscillation in which the longitudinal mode is a single mode is desirable, but in general, an SDH type laser device has a small light emitting layer volume. For this reason, it tends to be multimode. However, by increasing the volume of at least a part of the main light emitting part, i.e., the semiconductor stripe part, by increasing the resonator length, i.e., the stripe length of the semiconductor stripe part, the longitudinal mode of the oscillation light can be converted to a single mode. It is possible to avoid mode.

In the semiconductor laser device according to the present invention, when the light emitting layer volume is increased by increasing the resonator length, for example, by selecting the stripe length of the semiconductor stripe portion to be 300 μm or more, the oscillation light can be converted into a single mode. It becomes possible. The stripe length can be appropriately selected according to the scale of the apparatus.
For example, the stripe length (resonator length) is 300 μm to 500 μm unless an extremely high output is required depending on the oscillation mode required for the semiconductor laser device according to the present invention and the material constituting the stripe portion. It is considered that suitable oscillation characteristics can be obtained within a range.

In addition, the semiconductor laser device according to the present invention can be integrated, including a configuration using an SDH type semiconductor laser element. Therefore, a multi-wavelength light source for WDM (Wavelength Division Multiplexing) communication in a communication system application. Can also be used.
Further, in the SDH laser, the active layer width can be changed and the wavelength can be changed by changing the ridge width of the substrate. Therefore, the semiconductor laser device according to the present invention can be variously modified and changed, such as an array device of a multi-wavelength light source can be constituted by the semiconductor laser device according to the present invention.

It is a schematic sectional drawing of an example of the semiconductor laser apparatus by this invention. 2A to 2C are schematic cross-sectional views showing one process of a manufacturing method used for explaining a semiconductor laser device according to the present invention. It is a schematic sectional drawing of the conventional SDH type semiconductor laser apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser element (main part of semiconductor laser apparatus), 2 ... Base | substrate (substrate), 2b ... Ridge, 2c ... Ridge upper surface, 2d ... Ridge groove, 2e ... Ridge groove Bottom surface, 2f ... Ridge side surface, 3 ... Buffer layer, 3a ... Buffer layer, 4 ... First conductivity type cladding layer, 4a ... First conductivity type cladding layer, 5 ... Active Layer, 5a ... active layer, 6 ... second conductivity type cladding layer, 6a ... second conductivity type cladding layer, 7 ... current blocking layer, 8 ... second conductivity type cladding layer, DESCRIPTION OF SYMBOLS 9 ... Cap layer, 11 ... Electrode, 12 ... Electrode, 21 ... Semiconductor stripe part, 22 ... Slope, 23 ... Slope, 101 ... Conventional semiconductor laser apparatus, 102 ... Substrate (substrate), 102b ... ridge, 104 ... first conductivity type cladding layer, 104 ... 1st conductivity type cladding layer, 105 ... Active layer, 105a ... Active layer, 106 ... 2nd conductivity type cladding layer, 106a ... 2nd conductivity type cladding layer, 107 ... Current blocking layer, 108 ... second conductivity type cladding layer, 109 ... cap layer, 121 ... semiconductor stripe portion, 122 ... slope, 123 ... slope

Claims (7)

Striped ridges are formed on the {100} crystal plane of the GaAs substrate,
On the main surface having the ridge, at least a cladding layer, an active layer having GaAsSb, and a current blocking layer are formed,
A semiconductor stripe portion composed of at least the cladding layer and the active layer is formed on the ridge so as to have a triangular cross section sandwiched between slopes of {111} crystal planes,
A fault is formed between the active layer constituting the semiconductor stripe portion and the active layer constituting the other portion along the slope,
A semiconductor laser device comprising: a semiconductor laser element having a current blocking layer formed on both sides of the semiconductor stripe portion.   The semiconductor laser device according to claim 1, wherein the active layer contains N (nitrogen).   3. The semiconductor laser device according to claim 1, wherein the active layer contains Al.   The semiconductor laser device according to claim 1, wherein the active layer has a multi quantum well (MQW) structure.   2. The semiconductor laser device according to claim 1, wherein the crystal plane constituting the slope of the semiconductor stripe portion is a {111} B plane.   2. The semiconductor laser device according to claim 1, wherein a dimension in a longitudinal direction of the semiconductor stripe portion is 300 [mu] m or more.   2. The semiconductor laser device according to claim 1, wherein the emission wavelength band is changed by selecting the width of the semiconductor stripe portion.

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