JP2000340883A - Multiwavelength oscillating optical semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To implement stable and simultaneous oscillation of a plurality of different wavelengths without making the structure of an element large, by arranging a semiconductor gain waveguide, which has a plurality of quantum boxes each having a different size within an active region thereof, and a reflecting mirror which has a high reflectance with respect to a plurality of discrete wavelengths, in series with each other. SOLUTION: A semiconductor gain waveguide having a number of quantum boxes 1 to 3 each having a different size within an active region 4 thereof, and a reflecting mirror 5 having a high reflectance with respect to a plurality of discrete wavelengths are arranged in series with each other. As the above-mentioned reflecting mirror 5, a distribution reflecting mirror 5 wherein diffraction gratings, each having a gradually varied pitch, are cyclically formed is used. Further, the quantum boxes 1 to 3 are either quantum boxes 1 to 3 based on a Stranski-Krastanow mode, or quantum boxes 1 to 3 which are self-structured by an atomic layer epitaxy method. The quantum boxes 1 to 3 whose diameters are not uniform are formed at a high density, whereby multiwavelength oscillation can be implemented, and the intensity of multiwavelength oscillation light 8 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-wavelength oscillating optical semiconductor device, and more particularly to a multi-wavelength oscillating optical semiconductor device used as a light source in a wavelength division multiplexing communication system and capable of oscillating simultaneously at a plurality of different wavelengths. is there.

[0002]

2. Description of the Related Art With the rapid increase in the number of Internet users in recent years, maintenance of optical communication systems has been progressing at a rapid pace. However, a new form of service, such as receiving large-scale data such as moving images from a remote location when needed, is also starting to occur, and the exponential increase in traffic is expected at present. Is believed to reach.

[0003] In order to overcome such a situation, a shift to wavelength division multiplexing communication, in which light of a plurality of different wavelengths is introduced into one optical fiber, is called out, but this is regarded as the next generation communication means. Such a wavelength division multiplexing communication system naturally requires a light source that emits light of a plurality of different wavelengths.

Conventionally, as a multi-wavelength light source meeting such a demand, a large number of semiconductor lasers are arranged in a line and driven simultaneously, and an optical coupler is used to guide these plural wavelengths of light through a single optical fiber. Array-type lasers for guiding to a wave path are known.

Further, as another multi-wavelength light source, it has been proposed to realize multi-wavelength simultaneous oscillation by laminating active layers composed of quantum boxes having different oscillation wavelengths in a multilayer (if necessary, see Japanese Patent Application Laid-Open (JP-A) no. See JP-A-63-213384). For example, by controlling deposition conditions and the like so that the size of the quantum box in each active layer is different from each other, the oscillation wavelength in each active layer is different from each other.

Incidentally, such a quantum box (QD: Quant)
um Dot) is a box of potential that is extremely fine enough to give a carrier three-dimensional quantum confinement. In this quantum box, the state function density of the carrier is discretized as a delta function, and its ground level is Two carriers, for example, only two electrons can exist in the conduction band, and a plurality of electrons can exist in the excited level according to the order of the level. is there.

As a simple method of forming such a semiconductor quantum box, a method of self-forming is known. Specifically, a three-dimensional semiconductor is obtained by vapor-phase epitaxial growth of a lattice-mismatched semiconductor under certain conditions. The microstructure of
A method of self-forming a quantum box structure has been proposed (for example, see Japanese Patent Application No. 7-217466). In addition, as these self-forming methods, Transki-Klast
a method of forming a quantum box in an anov (Stransky-Krasnov) mode, a method of forming a quantum box in a Volmer-Webber (Volmer-Webber) mode,
Alternatively, a method of forming a self-assembled quantum box by alternately supplying materials using an ALE (atomic layer epitaxy) method is known.

[0008]

However, in the case of a conventional array type laser, there is a problem that a large number of independent stripe type laser structures are required in one element, and the element becomes large. In addition, it is necessary to precisely control the oscillation wavelength of each stripe laser, and a high-precision manufacturing technique is required to manufacture such an array laser.

On the other hand, in the case of a semiconductor laser having a multi-layered quantum box active layer, multi-wavelength oscillation is possible in principle, but it is considered that the structure is practically difficult to realize. That is, first, in order to equalize the oscillation wavelength of the quantum box in each active layer, it is necessary to equalize the diameter of the quantum box in each active layer, but this is not possible with the current growth technology.

Secondly, in order to make the oscillation wavelength match the design value, it is required to manufacture the quantum box by precisely controlling the diameter and composition thereof, but this is also difficult at present. Further, even if the above first and second requirements can be satisfied, there is a limit to multilayering, and there is a problem that the number of oscillating wavelengths is limited by the limit number of layers.

Accordingly, an object of the present invention is to perform stable oscillation at a plurality of different wavelengths simultaneously without increasing the size of the element structure.

[0012]

FIG. 1 is an explanatory view of the principle configuration of the present invention. Referring to FIG. 1, means for solving the problems in the present invention will be described. FIG.
(A) is a schematic sectional view of an optical semiconductor device,
FIG. 1B is a schematic enlarged view of a reflecting mirror provided in the optical semiconductor device. In the drawing, reference numerals 6 and 7 denote a one conductivity type cladding layer and a reverse conductivity type cladding layer, respectively. . 1 (a) and 1 (b) (1) According to the present invention, in a multi-wavelength oscillation optical semiconductor device, a semiconductor gain waveguide having a large number of quantum boxes 1 to 3 having different sizes in an active region 4 is provided. And a reflecting mirror 5 having high reflectivity at a plurality of wavelengths is arranged in series.

As described above, quantum boxes 1 to 3 having different sizes are provided.
That is, by using a semiconductor gain waveguide including a large amount of quantum boxes 1 to 3 having different diameters, simultaneous stimulated emission at multiple wavelengths can be achieved by increasing the amount of injected current. That is, for example, there are two quantum boxes 1 to 3 that perform light emission transition between levels at room temperature, for example, at a sufficiently small level of about 0.5 nm at room temperature. If they are separated from each other, the two quantum boxes 1 to 3 emit light independently of each other, and do not perform stimulated absorption and stimulated emission by the other light. These are quantum boxes 1-3
Has a completely discrete level, which is a big difference from the quantum well structure of one-dimensional confinement or two-dimensional confinement.

Further, by providing the reflecting mirror 5 having a high reflectance at a plurality of discrete wavelengths, it is possible to control the wavelength interval and the absolute wavelength of the multi-wavelength oscillating light 8 oscillated at irregular multiple wavelengths. Thus, it becomes suitable as a multi-wavelength light source for a multiplex optical communication system.

(2) Further, according to the present invention, in the above (1), the reflecting mirror 5 having a high reflectance at a plurality of discrete wavelengths.
The present invention is characterized in that a distributed reflector 5 in which a diffraction grating with a gradually changed pitch is periodically formed is used.

As described above, the reflecting mirror 5 having a high reflectance at a plurality of discrete wavelengths is provided by a super-periodic diffraction grating (SSG: Su).
(per Structure Grating), that is, a diffraction grating having a gradually changed pitch can be easily formed by using a distributed reflecting mirror in which a period is set to L and formed periodically. This SSG structure realizes high reflectivity at a plurality of wavelengths by adding even greater periodicity, that is, super-periodicity, to the periodicity of a basic diffraction grating structure (if necessary, HI
shii, et. al, IEEE, J. et al. QE, Vol.
32, no. 3, pp 433, 1996).

(3) In the present invention, in the above (1) or (2), the quantum boxes 1 to 3 may use the quantum boxes 1 to 3 based on the Stransky-Krasnov mode or the atomic layer epitaxy method. Quantum boxes 1-3 by self-organization
Or any one of the following.

As described above, the quantum boxes 1 to 1 suitable for multi-wavelength oscillation
As 3, quantum boxes 1 to 3 based on the Stranky-Clusteroff mode or quantum boxes 1 to 3 based on self-organization using the atomic layer epitaxy method are preferable. That is,
These self-forming methods can form the quantum boxes 1 to 3 at a high density, but it is difficult to make the diameters of the quantum boxes 1 to 3 uniform, and therefore, the quantum dot semiconductor laser oscillating at a single wavelength It is difficult to fabricate, but conversely, by taking advantage of this drawback, quantum boxes 1 to 3 having irregular diameters are formed at a high density, thereby enabling multi-wavelength oscillation, and In addition, the intensity of the multi-wavelength oscillation light 8 can be increased.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, a first embodiment of the present invention will be described with reference to FIGS. 2 to 4. First, a first embodiment of the present invention will be described with reference to FIGS. The manufacturing process of the embodiment will be described. Each drawing is a cross-sectional view along the optical axis direction of the laser light. Referring to FIG. 2A, first, an n-type GaAs substrate 11 having a (001) plane as a main surface.
After applying a photoresist (not shown) on the top and exposing a part of the photoresist to a lattice pattern having a periodically changed pitch using an electron beam exposure apparatus,
The photoresist is developed to form a lattice resist pattern, and then the n-type GaAs substrate 11 is etched using the lattice resist pattern as a mask to form the SSG structure 12. This SSG structure 1
As described above, the diffraction grating is periodically formed by setting the period of the diffraction grating whose pitch is gradually changed to L, as described above. This SSG structure 12 is used as a DBR mirror, that is, a distributed Bragg reflector. Used.

FIG. 2 (b) Next, MBE (Molecular Beam Epitaxy)
Using an apparatus, an n-type AlGaAs cladding layer 1 having a thickness of, for example, 0.9 μm and an Al composition ratio of, for example, 0.4 is used.
3. GaAs-SCH having a thickness of, for example, 0.1 μm
(Separate Confinment Het
erostructure) layer 14, having a thickness of, for example,
InGaAs waveguide layer 1 with 40 nm and In composition ratio of 0.1
GaAsSC having a thickness of, for example, 0.1 μm
The H layer 16 is sequentially grown.

Next, as shown in FIG. 2C, the GaAsSCH layer 16 and the InGaAs waveguide layer 15 grown on the region where the SSG structure 12 was not formed.
Is selectively removed to expose the GaAs SCH layer 14.

Next, referring to FIG. 3D, a Transski-layer is formed on the region where the GaAsSCH layer 16 and the InGaAs waveguide layer 15 are selectively removed.
After the quantum box waveguide layer 17 is formed by the Krastanov mode, the thickness is, for example, 0.1 μm GaAs.
The SCH layer 18 is grown to planarize the surface.

FIG. 3E is a diagram schematically showing, in an enlarged scale, the inside of the circle shown by the broken line in FIG. 3D, in which the quantum box waveguide layer 17 is formed. In the following, TMIn (trimethyl indium) and AsH ₃ were converted to InAs by 1 to ₃ with the growth temperature of 500 ° C. using MOVPE (metal organic chemical vapor deposition).
Simultaneous supply for 2ML (monolayer). At the beginning of this growth, two-dimensional growth occurs and InGaAs
An s wetting layer is formed, and when the thickness of the InGaAs wetting layer exceeds the elastic limit, a three-dimensional nucleus of an Angstrom order is discretely formed at a relatively high density on the surface of the InGaAs wetting layer. Further, when the growth is continued, InGa having a relatively large In composition ratio is used with the three-dimensional nucleus as a growth nucleus.
As quantum boxes 21 to 23 made of As are formed,
To 23 are InGa having a relatively small In composition ratio.
It becomes an As wetting layer. In the figure, the whole is collectively shown as an InAs layer 19.

This is because when the thickness of the InGaAs wetting layer exceeds the elastic limit, the InG composition ratio is relatively large.
By locally generating quantum boxes 21 to 23 made of aAs, the InGaAs growth layer as a whole becomes InGa
It is considered that the strain energy becomes lower than that in the case where the strain is generated on the entire surface of the As growth layer, and the crystal becomes crystallographically stable.

Next, a GaAs barrier layer 20 of, for example, 30 nm is grown, and this cycle is repeated, for example, three times to form the quantum box waveguide layer 17 having a three-layer structure. In this case, the quantum boxes 21 to 2
3 has an average diameter of about 20 nm and a surface coverage of about 10%.
Since this corresponds to an average distance between the quantum boxes 21 to 23 adjacent to each other being about 180 nm,
There is no undesired interaction between the quantum boxes 21 to 23 adjacent to each other.

Next, a p-type AlGaAs cladding layer 24 having a thickness of, for example, 1.2 μm and an Al composition ratio of, for example, 0.4, and a thickness of, for example, 0.3 μm p-type GaAs
After sequentially growing the s-contact layer 25, p-type GaAs
s contact layer 25 and p-type AlGaAs cladding layer 2
4 is etched to a depth of, for example, 1.2 μm to form a stripe-shaped mesa having a width of, for example, 2.5 μm in a direction perpendicular to the grooves of the diffraction grating constituting the SSG structure 12. The waveguide has a ridge structure.

Next, a p-side electrode 26 is provided so as to cover the p-type GaAs contact layer 25 and the side surfaces of the stripe-shaped mesas, and an n-side electrode 27 is formed on the back surface of the n-type GaAs substrate 11. Is cut to 1 μm, thereby completing a basic configuration of a multi-wavelength oscillation semiconductor laser in which a semiconductor gain waveguide including the quantum box waveguide layer 17 and a DBR mirror having the SSG structure 12 are arranged in series.

FIG. 4 is a perspective view of the multi-wavelength oscillation semiconductor laser formed in this manner. The p-side electrode 26 and the n-type GaAs substrate are provided so as to cover the side and top surfaces of the stripe-shaped mesa 28. 1
By injecting a current into the quantum box waveguide layer 17 from the n-side electrode 27 provided on the back surface of the quantum well 21, the quantum boxes 21 to 23 having different diameters have different wavelengths around 1.55 μm as center wavelengths. Stimulated emission occurs, of which only the discrete resonant wavelength of the SSG structure 12 becomes dominant, allowing multi-wavelength lasing at the lasing wavelengths and wavelength intervals defined by the SSG configuration 12. Further, in the above-described first embodiment, In which the quantum boxes 21 to 23 are formed is referred to as In.
Since the three As layers 19 are stacked, an active layer structure capable of having a sufficient gain is formed.

Next, a multi-wavelength oscillation semiconductor laser according to a second embodiment of the present invention will be described with reference to FIG. 5. In the second embodiment, the resonator is a DFB (distributed feedback) type. The other configuration is the same as that of the first embodiment. FIG. 5 is a perspective view of a multi-wavelength oscillation semiconductor laser according to a second embodiment of the present invention. As in the first embodiment, first, the (001) plane is used as a main surface. A photoresist (not shown) is applied on the n-type GaAs substrate 11, and a part of the photoresist is exposed to a lattice pattern having a periodically changed pitch using an electron beam exposure apparatus. The resist is developed to form a lattice-like resist pattern, and then the n-type GaAs substrate 11 is etched using the lattice-like resist pattern as a mask to form an SSG structure 12, and then the thickness is reduced using an MBE apparatus. For example, at 0.9 μm, the Al composition ratio is
For example, an n-type AlGaAs cladding layer 13 having a thickness of 0.4 and a GaAs SCH layer 1 having a thickness of 0.1 μm, for example.
4 is grown sequentially.

Next, using a growth method similar to that of the above-described first embodiment, a Transki-Krastan
After forming the quantum box waveguide layer 17 by the ov mode,
A GaAsSCH layer 18 having a thickness of, for example, 0.1 μm;
A p-type AlGaAs cladding layer 24 having a thickness of, for example, 1.2 μm and an Al composition ratio of, for example, 0.4;
A p-type GaAs contact layer 25 having a thickness of, for example, 0.3 μm is sequentially grown, and then a part of the p-type GaAs contact layer 25 and a part of the p-type AlGaAs cladding layer 24 are etched to a depth of, for example, 1.2 μm. Then S
In the direction perpendicular to the grooves of the diffraction grating constituting the SG structure 12,
A stripe-shaped mesa having a width of, for example, 2.5 μm is formed to form a waveguide having a ridge structure.

Next, the p-side electrode 2 is formed so as to cover the side surfaces of the p-type GaAs contact layer 25 and the stripe-shaped mesa 28.
6 and n-type GaAs substrate 11
The side electrode 27 was formed, and then cleaved so that the resonator length became 1 μm, whereby the semiconductor gain waveguide including the quantum box waveguide layer 17 and the DFB resonator including the SSG structure 12 were arranged in series. The basic configuration of the multi-wavelength oscillation semiconductor laser is completed.

In the second embodiment, the DFB
The SSG structure 12 constituting the resonator enables simultaneous oscillation at a predetermined oscillation wavelength and at multiple wavelengths at predetermined wavelength intervals. In the second embodiment, D
Unlike the case of the BR structure, since the quantum box waveguide layer 17 extends on the SSG structure 12, the step of growing the InGaAs waveguide layer and the step of selectively removing the same become unnecessary.
Thereby, the manufacturing process is further simplified.

The embodiments of the present invention have been described above. However, the present invention is not limited to the configurations and conditions described in the embodiments, and various changes can be made. For example, in the description of each of the above-described embodiments, a self-forming method by the Transki-Krastanov mode in which quantum boxes having high density and irregular diameters are easily formed is used as a method of forming quantum boxes.
-The method is not limited to the self-forming method by the Krastanov mode, and a method by self-organization using the ALE method may be used.

In the case of using the self-assembly method by the ALE method, for example, after forming a GaAsSCH layer 14, an In material such as TMIn is supplied alone to form an In metal island on the surface of the GaAsSCH layer 14. It is formed discretely. Next, when a Ga raw material such as TMGa (trimethylgallium) is supplied alone, GaAsS
Ga metal islands are discretely formed on the surface of the CH layer 14, and In and Ga are mixed on the In metal island to form I metal.
An n + Ga metal island is formed.

Next, when As material such as AsH ₃ is supplied alone, restructuring (Reconstruct) is performed on the surface.
) occurs, and an InGaAs quantum box having a relatively large In composition ratio is formed in the In + Ga metal island,
In the Ga metal island and its vicinity, an InGaAs layer having a relatively small In composition ratio is formed. By repeating such a cycle several times, a final quantum box waveguide layer is formed.

As described above, even when the method based on self-organization using the ALE method is used, the Transki-Kra
Similar to the self-forming method by the Stanov mode, a quantum box having a high density and an irregular diameter is easily formed, thereby enabling multi-wavelength oscillation.

In the description of each of the above embodiments, the SSG structure 12 is formed directly on the n-type GaAs substrate. However, an n-type GaAs buffer layer is provided on the n-type GaAs layer 11 and the n-type GaAs buffer layer is provided. It may be provided on the GaAs buffer layer 11, or may be formed on the n-type AlGaAs cladding layer 13 if measures are taken against the formation of a self-oxidized film.

In the above embodiments, the ridge structure is formed by forming the stripe-shaped mesas 28, but the stripe-shaped structure is a BH (buried heterojunction).
It goes without saying that other known stripe-shaped structures such as a structure may be used.

In the description of each embodiment of the present invention, the quantum box is described as an InGaAs quantum box, but it is in principle self-evident that the quantum box may be made of another III-V compound semiconductor. It is apparent that the present invention can be applied to other compound semiconductors such as II-VI compound semiconductors or IV-VI compound semiconductors.

[0040]

According to the present invention, a quantum box waveguide is constructed using quantum boxes having high density and irregular diameters, and a plurality of discretes such as SSG are serially connected to the quantum box waveguide. Since a reflector with high reflectivity at wavelength is arranged, the simple structure enables stable simultaneous oscillation at multiple wavelengths with controlled oscillation wavelength and wavelength interval, thereby increasing the size of the element. Therefore, it is possible to obtain a stable multi-wavelength light source without any need, and thus greatly contribute to the realization of a wavelength multiplex communication system.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of the present invention.

FIG. 2 is an explanatory diagram of a manufacturing process partway through the first embodiment of the present invention.

FIG. 3 is an explanatory view of a manufacturing process of the first embodiment of the present invention after FIG. 2;

FIG. 4 is a perspective view of the multi-wavelength oscillation semiconductor laser according to the first embodiment of the present invention.

FIG. 5 is a perspective view of a multi-wavelength oscillation semiconductor laser according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Quantum box 2 Quantum box 3 Quantum box 4 Active region 5 Reflector 6 One conductivity type cladding layer 7 Reverse conductivity type cladding layer 8 Multi-wavelength oscillation light 11 n-type GaAs substrate 12 SSG structure 13 n-type AlGaAs cladding layer 14 GaAsSCH layer 15 InGaAs waveguide layer 16 GaAsSCH layer 17 quantum box waveguide layer 18 GaAsSCH layer 19 InAs layer 20 GaAs barrier layer 21 quantum box 22 quantum box 23 quantum box 24 p-type AlGaAs cladding layer 25 p-type GaAs contact layer 26 p-side electrode 27 n Side electrode 28 Striped mesa

Claims (3)

[Claims] 1. A semiconductor gain waveguide having a large number of quantum boxes having different sizes in an active region, and a reflector having a high reflectance at a plurality of discrete wavelengths are arranged in series. Multi-wavelength oscillation optical semiconductor device. 2. A distributed mirror in which a diffraction grating whose pitch is gradually changed is formed periodically as said reflecting mirror having a high reflectance at a plurality of discrete wavelengths. Item 2. The multi-wavelength oscillation optical semiconductor device according to Item 1. 3. The quantum box according to claim 1, wherein the quantum box is any one of a quantum box based on a Stranky-Krasnov mode and a quantum box based on self-organization using an atomic layer epitaxy method. 2. The multi-wavelength oscillation optical semiconductor device according to 1.