JP2000196193A - Semiconductor device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the structure of a semiconductor device having a quantum dot for controlling the luminous wavelength of the quantum dot, and its manufacturing method. SOLUTION: A semiconductor device is composed of a semiconductor substrate 10, a buffer layer 12 that is formed on the semiconductor substrate 10 while a lattice constant near the surface differs from that near the interface with the semiconductor substrate 10, and a quantum dot that is formed on the buffer layer 12 while a luminous wavelength is stipulated by a lattice constant near the surface of the buffer layer 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor device and a method for manufacturing the same, and more particularly, to a semiconductor device having quantum dots and a method for manufacturing the same.

[0002]

2. Description of the Related Art With the progress of semiconductor processes, nano-scale film formation technology and fine processing technology have been used for manufacturing semiconductor devices. With the progress of such film formation technology and microfabrication technology, the degree of integration of a semiconductor integrated circuit has been improved, and an element utilizing a quantum mechanical effect, for example, an HBT (hetero bipolar transistor: He
Tero Bipolar Transistors) and quantum well lasers have also been put to practical use.

In recent years, quantum dots have been attracting attention as the ultimate material utilizing the quantum mechanical effect. Quantum dots are potential boxes that are extremely fine enough to give three-dimensional quantum confinement to carriers. A quantum dot has a state density of a delta function, and only two carriers can enter the ground level of one quantum dot.

As one of the methods utilizing such characteristics of the quantum dot, it has been proposed to use the quantum dot for an active region of a semiconductor laser. That is, in the semiconductor laser having the quantum well structure, the limit of the characteristic improvement in the oscillation threshold and the temperature characteristic of the threshold has been pointed out. However, by applying the quantum dots to the active layer, electrons, holes, and light are reduced. And the interaction with
The oscillation threshold and the temperature characteristics of the threshold can be improved. In addition, quantum dot memories using blue chirp modulators and wavelength conversion elements, single electron transistors and hole burning effects have been proposed, and research on creating next-generation elements using quantum dots has been actively conducted. .

As a technique for forming such a quantum dot, there is a technique using a fine processing technique. For example,
Lithography using an electron beam, a method of forming a quantum dot structure at the bottom of a tetrahedral hole etched on a mask pattern, a method of utilizing the initial lateral growth on a fine inclined substrate, an STM (scanning tunnel) A method using atomic manipulation that applies a microscope (Scanning Tunneling Microscope) technology has been proposed. These methods have an advantage that the position at which the quantum dot is formed can be arbitrarily controlled because of the common feature of artificial processing. However, the number density cannot exceed the precision limit of the fine processing technology, and the uniformity was also extremely low.

[0006] As a new technology that is a breakthrough for producing quantum dots, a technology for self-forming quantum dots has recently been found. This is because a lattice-mismatched semiconductor is grown by vapor phase epitaxy under certain conditions.
This uses a phenomenon in which a three-dimensional fine structure (quantum dot) is self-formed. This method is extremely easy to implement compared to microfabrication, and the resulting quantum dots have extremely high uniformity beyond the precision limits of artificial processing techniques, high number density, and high quality. is there. Devices such as semiconductor lasers have actually been reported using such self-formed quantum dots, and the possibility of quantum dot elements has become a reality.

[0007] Several modes of formation of quantum dots are known. The most well-known formation mode is the Stranski-Krastanov mode (hereinafter “S
-K mode ". ) Mode. This is a mode in which a semiconductor crystal to be epitaxially grown grows two-dimensionally (film growth) at the beginning of the growth, but grows three-dimensionally when the elastic limit of the film is exceeded. This mode is the easiest of the self-forming modes and is commonly used. According to this mode, quantum dots can be formed with a high number density.

Further, as another forming mode, Volmer-W
A mode called an ebber mode is known. In this mode, three-dimensional growth is performed from the beginning without initial two-dimensional growth. This mode is generally said to occur at a lower temperature than the SK mode, but it is difficult to obtain high quality dots, and practically little research has been done.

As a new method for producing quantum dots using the self-assembly mode, the proximity lamination method has attracted attention. Proximity lamination is a process in which several three-dimensional structures created by the method described above are laminated in the growth direction via a thin intermediate layer that is small enough to allow carriers to tunnel, and these are united to form tall quantum dots. How to According to this method, quantum dots with high uniformity can be formed.

[0010]

As described above, various methods have been found for techniques for forming quantum dots. However, considering the application of quantum dots to devices, it is essential to control the energy of the quantum dots. For example, in consideration of applying a semiconductor laser using quantum dots as a laser light source for optical communication, a laser having an emission wavelength of 1.3 μm (0.95 eV) or 1.55 μm (0.8 eV) must be created. Must be formed of InAs formed on a GaAs substrate.
Alternatively, in the case of an InGaAs quantum dot, its band gap energy is about 1.1 to 1.3 eV, and this quantum dot could not be used for optical communication.

Also, in the case of a quantum dot formed by the close-stacking method, as in the case of a single SK mode, Ga
In the case where quantum dots of InAs or InGaAs were formed on an As substrate, it was about 1.1 to 1.3 eV, and could not be used for optical communication. An object of the present invention is to provide a structure of a semiconductor device capable of controlling the emission wavelength of a quantum dot and a method of manufacturing the same.

[0012]

The object of the present invention is to provide a semiconductor substrate, a buffer layer formed on the semiconductor substrate, and having a lattice constant near a surface different from a lattice constant near an interface with the semiconductor substrate; And a quantum dot layer formed on the layer.

In the above-mentioned semiconductor device, the quantum dot layer may have an emission wavelength defined by a lattice constant near the surface of the buffer layer. In the above-described semiconductor device, a lattice constant near the surface of the buffer layer may be larger than a lattice constant near an interface with the semiconductor substrate.

In the above-mentioned semiconductor device, the quantum dots may be constituted by three-dimensionally grown islands self-formed in SK mode. In the above-described semiconductor device, the quantum dots may be stacked in plural with an intermediate layer interposed therebetween. In the above-described semiconductor device, the thickness of the intermediate layer may be smaller than the height of the quantum dots.

In the above-mentioned semiconductor device, the quantum dots may be made of InAs or InGaAs. In the above-described semiconductor device, the semiconductor substrate may be a GaAs substrate, and the buffer layer may be an InGaAs layer. Also,
In the above semiconductor device, the quantum dot may constitute an active layer of a semiconductor laser.

The object of the present invention is to form a buffer layer having a lattice constant near the surface different from the lattice constant near the interface with the semiconductor substrate on the semiconductor substrate; Forming a quantum dot defined by a lattice constant near the surface of the buffer layer.

In the method of manufacturing a semiconductor device described above, in the step of forming the quantum dot, the quantum dot formed of a three-dimensionally grown island may be self-formed in an SK mode. In the method of manufacturing a semiconductor device described above, in the step of forming the quantum dots, the quantum dots formed by agglomerating into a dot shape in a film may be formed.

In the method of manufacturing a semiconductor device, in the step of forming the quantum dots, a plurality of quantum dots may be stacked with an intermediate layer interposed therebetween. In the method of manufacturing a semiconductor device described above, in the step of forming the buffer layer, a lattice constant in the vicinity of the surface may be controlled so that an emission wavelength of the quantum dot has a desired wavelength.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Principle of the Present Invention] First, the principle of the present invention will be described with reference to FIGS. FIG.
FIG. 2 is a schematic sectional view showing the structure and manufacturing method of a conventional semiconductor device, FIG. 2 is a schematic sectional view showing the principle of the semiconductor device of the present invention, and FIG.
5 is a graph showing the relationship between the n composition and the emission wavelength of a quantum dot.

In describing the principle of the present invention, a case where quantum dots made of InAs are formed on a GaAs substrate will be described as an example. However, the present invention can be similarly applied to other material systems. In a conventional method for manufacturing a semiconductor device, as shown in FIG. 1, a GaAs buffer layer is formed on a GaAs substrate, and then several atomic layers of I
By supplying nAs, quantum dots made of InAs were self-formed on the GaAs buffer layer. Ga
When several atomic layers of InAs are supplied on the As buffer layer,
Since the lattice constants of InAs and GaAs are different, a thin I
In terms of energy, nAs is more energy stable when InAs or InGaAs in which some Ga is taken in from GaAs of the substrate are formed and aggregated, rather than being uniformly distributed on the GaAs buffer layer. Therefore, quantum dots made of InAs are formed on the GaAs buffer layer.

Here, in order to obtain a quantum dot having a long emission wavelength, the growth condition is adjusted to increase the size of the quantum dot, or the quantum dots are effectively stacked by laminating the quantum dots in close proximity. It is effective to increase. On the other hand, increasing the size of the quantum dot narrows the energy level interval of the quantum dot, and from the original purpose of the quantum dot, which concentrates carriers only at the ground level and improves the performance of the laser or nonlinear element. There is a risk of deviation. For this reason, when forming a quantum dot by the above-mentioned conventional method of manufacturing a semiconductor device, it has been a limit to control the emission wavelength within a range of about 1.1 to 1.2 μm at room temperature.

As a result of the inventor's intensive studies in such a background, the size and composition of the quantum dots are determined by the difference in surface energy due to the lattice mismatch with the underlayer, and the lattice mismatch with the underlayer is determined. It has been clarified for the first time that the emission wavelength (energy band gap) of a quantum dot can be controlled by controlling the amount. The amount of lattice mismatch can be controlled by forming a buffer layer having a different lattice constant from the substrate between the substrate and the quantum dots. For example, in the above example, as shown in FIG.
An InGaAs buffer layer 1 made of InGaAs having a lattice constant larger than that of GaAs instead of the As buffer layer
2, the amount of lattice mismatch can be controlled by appropriately controlling the composition of the InGaAs buffer layer 12.

The effect of providing the InGaAs buffer layer 12 is to increase the in-plane lattice constant on the surface of the buffer layer 12. That is, the In film having a thickness greater than the critical film thickness for strain relaxation is used.
By depositing the GaAs buffer layer 12 on the GaAs substrate 10, the amount of strain caused by the generation of dislocations is reduced, and the in-plane lattice constant on the surface of the buffer layer 12 increases (see FIG. 2). On the other hand, GaAs is
When a buffer layer is deposited, no distortion or change in lattice constant occurs (see FIG. 1).

Therefore, the InGaAs buffer layer 12
By depositing, the in-plane lattice constant on the surface of the buffer layer 12 can be controlled, and as a result, the emission wavelength of the quantum dots 14 can be controlled. FIG.
In a sample in which a quantum dot layer including InGaAs quantum dots is formed on an InGaAs buffer layer by alternately supplying InAs and GaAs at the atomic layer level using a MOVPE apparatus, the In composition of the InGaAs buffer layer and the quantum This shows the relationship with the emission wavelength of the dot. As shown in the figure, the emission wavelength of the quantum dot increases as the In composition of the InGaAs buffer layer increases, and it can be seen that the emission wavelength can be shifted to a longer wavelength side than the conventional quantum dot by providing the InGaAs buffer layer. Was. Although not shown, InGa
Similar results were obtained when quantum dots were formed on the As buffer layer in the normal SK mode.

Hereinafter, the present invention will be described in detail with reference to embodiments. [First Embodiment] The semiconductor device and the method for fabricating the same according to a first embodiment of the present invention will be explained with reference to FIGS. FIG. 4 is a schematic sectional view showing the structure of the semiconductor device according to the present embodiment, and FIGS. 5 and 6 are process sectional views showing the method for manufacturing the semiconductor device according to the present embodiment.

First, the structure of the semiconductor device according to the present embodiment will be explained. On the GaAs substrate 10, a buffer layer 12 of In _0.2 Ga _0.8 As with a thickness of about 500 nm is formed. On the buffer layer 12, InA
The quantum dot layer 18 is formed by repeatedly stacking the quantum dots 14 made of s and the intermediate layer 16 made of a GaAs layer. On the quantum dot layer 18, InGaAs
s is formed. Thus, the quantum dots 14 made of InAs are formed on the GaAs substrate 10.

As described above, in the semiconductor device according to the present embodiment, the buffer layer 12 provided between the GaAs substrate 10 and the quantum dot layer 18 is composed of In _0.2 Ga _0.8 As having a larger lattice constant than GaAs. And the lattice constant on the surface of the buffer layer 12 is larger than that of the GaAs substrate 10. Thereby, the emission wavelength of the quantum dots 14 formed on the buffer layer 12 can be shifted to the longer wavelength side.

Photoluminescence measurement of the semiconductor device shown in FIG. 4 at room temperature showed that the emission wavelength of the quantum dot was about 1.3 μm. In contrast, In _0.2 G
In the sample in which the quantum dots were formed using the GaAs buffer layer instead of the a _0.8 As buffer layer, the emission wavelength of the quantum dots was about 1.2 μm. Therefore, GaAs
It has been clarified that the emission wavelength of the quantum dot can be shifted to a longer wavelength side by using an In _0.2 Ga _0.8 As buffer layer instead of the buffer layer.

Next, the method for fabricating the semiconductor device according to the present embodiment will be explained with reference to FIGS. First, G
On the aAs substrate 10, for example, an In _0.2
A buffer layer 12 of Ga _0.8 As is deposited (FIG. 5).
(A)). The substrate temperature is, for example, 500 ° C. The thickness of the buffer layer 12 is desirably a thickness sufficient to make the lattice constant on the surface of the buffer layer 12 different from the lattice constant of the GaAs substrate 10, that is, a thickness greater than or equal to the critical thickness for strain relaxation. In the case of InGaAs having the above composition,
For example, the buffer layer 12 having a lattice constant of the surface region different from that of GaAs can be formed with a thickness of about 500 nm. Note that the thickness of the buffer layer 12 is desirably adjusted as appropriate according to the composition of the buffer layer 12.

Next, on the buffer layer 12, for example, MB
By the E method, quantum dots made of InAs are self-formed in the SK mode (FIG. 5B). For example, the growth rate is 0.1 μm / h, the As pressure is 1.2 × 10 ⁻⁵ Torr,
The substrate temperature is set to 650 ° C. and 1.8 ML (atomic layer: monola
yer) After supplying a considerable amount of InAs, the supply of the raw material is interrupted for about one minute to promote three-dimensional growth. Thus, In
Quantum dots made of InAs are formed on a _0.2 Ga _0.8 As buffer layer.

The quantum dots formed in the SK mode are connected to each other by a thin layer called a wetting layer, as shown in FIG. Therefore, it can be determined whether or not the layer has grown in the SK mode based on the presence or absence of the wetting layer. Next, on the quantum dots 14 thus formed, for example, by the MBE method,
An intermediate layer 16 made of GaAs is formed (FIG. 5).
(C)). For example, a growth rate of 0.75 μm / h, As
The pressure was set to 6 × 10 ⁻⁶ Torr and the substrate temperature was set to 510 ° C.
After supplying GaAs equivalent to ML, the supply of the raw material is interrupted for about 2 minutes to promote the growth. Thereby, the intermediate layer 16 is formed so that the region between the quantum dots 14 is buried.

When the thickness of the intermediate layer is reduced to a level smaller than the height of the quantum dots 14, the plurality of quantum dots 14 stacked close to each other in the film formation direction functions as one quantum dot. That is, the effective size of the quantum dot 14 increases. As a result, the quantum size effect is weakened, and the emission wavelength shifts to the longer wavelength side. Therefore, the emission wavelength can be shifted to a longer wavelength side by laminating the quantum dots 14 in close proximity.

Then, 0.7 ML of InAs and 3 ML of GaAs are repeatedly deposited, for example, eight times by the same procedure as above, for example, by the MBE method, and the quantum dot layer 18 in which the quantum dots 14 are closely stacked is formed. Is formed (FIG. 6A). Next, a cladding layer 20 of about 30 nm in thickness made of InGaAs is formed on the quantum dot layer 18 by, for example, the MBE method.

Thus, the semiconductor device shown in FIG. 4 is manufactured. As described above, according to the present embodiment, since the buffer layer having a lattice constant on the surface side different from the lattice constant of the substrate is provided between the substrate and the quantum dots, the emission of the quantum dots is controlled by controlling the composition of the buffer layer. The wavelength can be controlled. Further, InAs or InGa is formed on a GaAs substrate.
In a system for forming quantum dots made of As, by interposing an InGaAs buffer layer between them, it is possible to form quantum dots having an emission wavelength of 1.3 μm or more used for optical communication.

[Second Embodiment] The semiconductor device according to a second embodiment of the present invention will be explained with reference to FIGS. FIG. 7 is a schematic sectional view showing the structure of the semiconductor device according to the present embodiment, and FIGS. 8 and 9 are process sectional views showing the method of manufacturing the semiconductor device according to the present embodiment. In this embodiment,
A case in which the quantum dot according to the present invention is applied to a laser device will be described.

First, the structure of the semiconductor device according to the present embodiment will be explained with reference to FIG. On the n-GaAs substrate 30, n-In _0.1 Ga _0.9 A having a thickness of about 500 nm is formed.
A buffer layer 32 of s is formed. On the buffer layer 32, n-In _0.5 Ga having a thickness of about 1400 nm is formed.
_A cladding layer 34 of _0.5 P is formed. On the cladding layer 34, In _0.05 Ga having a thickness of about 100 nm is formed.
_An SCH layer 36 of _0.95 As is formed. SC
On the H layer 36, the I layer including the InGaAs quantum dots 38
An active layer 40 made of an nGaAs layer is formed. On the active layer 40, an In _0.05 Ga _0.95 layer having a thickness of about 100 nm is formed.
The SCH layer 42 made of As is formed. On the SCH layer 42, p-In _0.5 Ga _0.5 having a thickness of about 1400 nm is formed.
A cladding layer 44 made of P is formed. On the cladding layer 44, a 400 nm-thick p-In _0.05 Ga _0.95
A contact layer 46 made of As is formed.

As described above, in the semiconductor device according to the present embodiment, since the quantum dot active layer is applied as the active layer 40 of the semiconductor laser, the interaction between electrons / holes and light is made as efficient as possible. And the temperature characteristics of the oscillation threshold and the threshold can be improved. In addition, the emission wavelength of the quantum dot active layer can be appropriately controlled by controlling the composition ratio of the buffer layer 32 corresponding to the buffer layer 12 of the first embodiment. That is, by appropriately controlling the composition of the InGaAs layer constituting the buffer layer 32, a 1.3 μm band suitable for optical communication or 1.
It is also possible to configure a semiconductor laser having an emission wavelength in the 55 μm band. For example, the above In _0.1 Ga _0.9 A
By forming the buffer layer 32 with s, the in-plane lattice constant on the buffer layer 32 becomes larger than that of GaAs, and the lattice constant thus obtained can be reflected on the upper layer film. Therefore, the In of the buffer layer 32
By appropriately controlling the composition, the emission wavelength of the quantum dot can be controlled to 1.3 μm or 1.55 μm.

Next, the semiconductor device according to the present embodiment is manufactured.
The method will be described with reference to FIGS. First, n
On the GaAs substrate 30, for example, by the MOVPE method,
N-In with a thickness of about 500 nm_0.1Ga_0.9As layer and film thickness
About 1400 nm n-In_0.5Ga_0.5P layer and film thickness about 1
00 nm In_0.05Ga_0.95An As layer is sequentially deposited.
Group III raw materials include, for example, trimethylindium
(TMI), trimethylindium dimethylethylamine
Adduct (TMIDMEA), triethylgallium
(TEG) as a group V raw material, for example, arsine
(AsH_Three) Can be used. In addition, the base during film formation
The plate temperature is, for example, 500 ° C. Thus, n-GaAs
On the s substrate 30, n-In_0.1Ga_0.9A bag made of As
Layer 32 and n-In _0.5Ga_0.5Cladding made of P
Layer 34 and In_0.05Ga_0.95SCH layer 36 made of As
(FIG. 8A).

Next, on the SCH layer 36, for example, MOV
The active layer 40 is formed by the PE method. For example, the substrate temperature is set to 500 ° C., and InAs and GaAs are alternately supplied at the atomic layer level to form a film.
An active layer 40 made of an InGaAs layer including s quantum dots 38 is formed. When InGaAs is formed by alternately supplying InAs and GaAs, quantum dots 38 formed by aggregating InGaAs having a high In composition are formed in the film. Thus, the quantum dots 3 on the SCH layer 36
8 can be formed (FIG. 8).
(B)).

Next, on the active layer 40, for example, MOVP
E method, In _0.05 Ga _0.95 As with a thickness of about 100 nm
A layer, a p-In _0.5 Ga _0.5 P layer having a thickness of about 1400 nm, and a p-In _0.05 Ga _0.95 As layer having a thickness of 400 nm are sequentially deposited. The substrate temperature during film formation is, for example, 500 ° C. Thus, on the active layer 40, In _0.05 Ga _0.95 As
The SCH layer 42 made of p-In _0.5 Ga _0.5 P and the contact layer 46 made of p-In _0.05 Ga _0.95 As are formed (FIG. 9).

Thus, the semiconductor device shown in FIG. 7 is formed. As described above, according to the present embodiment, in the semiconductor laser having the active layer formed of the quantum dot layer, the emission wavelength of the quantum dot is controlled by the base film forming the SCH layer. Can be improved, and the emission wavelength can be made longer. Thereby, 1.3 μm suitable for optical communication
It is also possible to configure a semiconductor laser having an emission wavelength in the band or the 1.55 μm band.

[Modified Embodiment] The present invention is not limited to the above-described embodiment, and various modifications can be made. In the above embodiment,
On a GaAs substrate, an InGaAs buffer layer and an InA
Although the case of forming quantum dots of s or InGaAs has been described as an example, the present invention can be similarly applied to a semiconductor device of another material. That is, in the present invention, in a semiconductor device having quantum dots formed on a semiconductor substrate via a buffer layer, a semiconductor layer having a lattice constant different from that of the substrate is applied as a buffer layer, and the semiconductor layer has The light emission wavelength of the quantum dot is controlled by controlling the lattice constant, and is not limited to the above-described material system. For example, the present invention can be similarly applied to not only a GaAs-based semiconductor but also an InP-based or other compound semiconductor, or a semiconductor such as Si or Ge. Further, as a semiconductor layer constituting the quantum dot, InAs, InGaAs, other
A group II-VI or group III-V compound semiconductor can be used. The material forming the buffer layer may be appropriately selected from semiconductor materials having a different lattice constant from the semiconductor substrate but capable of epitaxial growth while relaxing the strain. Further, as a material forming the quantum dot, S
A material in which quantum dots are self-formed in the -K mode may be appropriately selected.

In the first embodiment, the quantum dots are formed by the proximity lamination method, but it is not always necessary to perform the proximity lamination. For example, a single quantum dot layer in the SK mode may be formed, or multiple quantum dots may be stacked via a thick intermediate layer. Further, in the second embodiment, the example in which the quantum dot configured according to the present invention is applied to the active layer of the semiconductor laser has been described. However, a quantum dot such as a blue chirp modulator, a wavelength conversion element, or a quantum dot memory is The present invention can be similarly applied to various devices.

The above effects obtained by the present invention do not depend on the method of forming the quantum dots, but generally, the emission wavelength of the quantum dots changes depending on the method of forming the films. Therefore, it is desirable to appropriately select and adjust the film formation method and the film formation conditions of the quantum dots according to characteristics such as a desired emission wavelength.

[0045]

As described above, according to the present invention, a buffer layer having a lattice constant near the surface different from that near the interface with the semiconductor substrate is provided on the semiconductor substrate.
Since the quantum dots are formed on the buffer layer, the emission wavelength of the quantum dots can be defined by the lattice constant near the surface of the buffer layer. Thereby, the emission wavelength of the quantum dot can be shifted to the longer wavelength side, and GaAs
With the quantum dots formed on the s substrate, it is possible to form quantum dots having an emission wavelength in the 1.3 μm band or the 1.55 μm band, which have been difficult to realize conventionally.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a structure and a manufacturing method of a conventional semiconductor device.

FIG. 2 is a schematic sectional view showing the principle of the semiconductor device of the present invention.

FIG. 3 shows In of a buffer layer in the semiconductor device of the present invention.
4 is a graph showing a relationship between a composition and an emission wavelength of a quantum dot.

FIG. 4 is a schematic sectional view showing the structure of the semiconductor device according to the first embodiment of the present invention.

FIG. 5 is a process sectional view (part 1) illustrating the method for fabricating the semiconductor device according to the first embodiment of the present invention;

FIG. 6 is a sectional view (part 2) illustrating the method for manufacturing the semiconductor device according to the first embodiment of the present invention;

FIG. 7 is a schematic sectional view illustrating a structure of a semiconductor device according to a second embodiment of the present invention.

FIG. 8 is a process sectional view (part 1) illustrating the method for fabricating the semiconductor device according to the second embodiment of the present invention.

FIG. 9 is a process sectional view (part 2) illustrating the method for fabricating the semiconductor device according to the second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... GaAs substrate 12 ... InGaAs buffer layer 14 ... quantum dot 16 ... intermediate layer 18 ... quantum dot layer 20 ... cladding layer 30 ... n-GaAs substrate 32 ... buffer layer 34 ... cladding layer 36 ... SCH layer 38 ... quantum dot 40 ... Active layer 42 SCH layer 44 Cladding layer 46 Contact layer 50 GaAs substrate 52 GaAs buffer layer 54 Quantum dot

Claims (14)

[Claims] A semiconductor substrate, a buffer layer formed on the semiconductor substrate, wherein a lattice constant near a surface is different from a lattice constant near an interface with the semiconductor substrate, and a quantum dot formed on the buffer layer And a semiconductor device. 2. The semiconductor device according to claim 1, wherein the quantum dot layer has an emission wavelength defined by a lattice constant near the surface of the buffer layer. 3. The semiconductor device according to claim 1, wherein a lattice constant near a surface of the buffer layer is larger than a lattice constant near an interface with the semiconductor substrate. 4. The semiconductor device according to claim 1, wherein the quantum dots are formed by a three-dimensionally grown island self-formed in an SK mode. 5. The semiconductor device according to claim 1, wherein a plurality of the quantum dots are stacked with an intermediate layer interposed therebetween. 6. The semiconductor device according to claim 5, wherein the thickness of the intermediate layer is smaller than the height of the quantum dots. 7. The semiconductor device according to claim 1, wherein the quantum dots are made of InAs or InGaAs. 8. The semiconductor device according to claim 1, wherein said semiconductor substrate is a GaAs substrate, and said buffer layer is an InGaAs layer. 9. The semiconductor device according to claim 1, wherein the quantum dot is an active layer of a semiconductor laser. 10. A step of forming a buffer layer on a semiconductor substrate, the lattice constant near the surface being different from the lattice constant near the interface with the semiconductor substrate; and forming, on the buffer layer, an emission wavelength of the buffer layer. Forming quantum dots defined by a lattice constant in the vicinity of the surface. 11. The method of manufacturing a semiconductor device according to claim 10, wherein, in the step of forming the quantum dots, the quantum dots formed of three-dimensional growth islands are self-formed in an SK mode. Device manufacturing method. 12. The semiconductor device manufacturing method according to claim 10, wherein, in the step of forming the quantum dots, the quantum dots formed in the film by being aggregated in a dot shape are formed. Device manufacturing method. 13. The method of manufacturing a semiconductor device according to claim 10, wherein, in the step of forming the quantum dots, a plurality of quantum dots are stacked with an intermediate layer interposed therebetween. Semiconductor device manufacturing method. 14. The method of manufacturing a semiconductor device according to claim 10, wherein, in the step of forming the buffer layer, the emission wavelength of the quantum dots is set to a desired wavelength. A method for manufacturing a semiconductor device, comprising controlling a lattice constant in the vicinity of a surface.