JP2006080293A - Forming method of quantum dot - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of realizing self-formation of highly uniform quantum dots with a high density. <P>SOLUTION: A GaAs buffer layer is formed on a GaAs substrate, a GaSb<SB>x</SB>As<SB>1-x</SB>(0<x≤1) layer is introduced onto the GaAs buffer, and InAs quantum dots are self-formed on the a GaSb<SB>x</SB>As<SB>1-x</SB>(0<x≤1) layer. For example, in the case of introducing a GaSb layer with 0.24 to 1.52 ML thickness with a composition x (x=1) of antimony (Sb) to the GaAs buffer layer, the InAs quantum dots can be self-formed on the GaSb layer with a high uniformity with a dot density of 1.1×10<SP>11</SP>cm<SP>-2</SP>or over. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming quantum dots, and more particularly to a method for self-forming high-density and uniform quantum dots.

  In recent years, application of quantum dots to optoelectronic devices has attracted attention, and various studies and developments have been made. Quantum dots, which are three-dimensional carrier confinement structures, have a much higher carrier energy spectrum than quantum well structures, which are one-dimensional confinement carriers, and quantum wire structures, which are two-dimensional confinement structures. Sharp and discrete. Even at room temperature, carrier transitions occur discontinuously between quantum levels, and a sharp emission spectrum can be obtained.

  For the formation of quantum dots, a method using so-called SK (Stranski-Krastanov) mode growth that appears in the early stage of heteroepitaxial growth is generally employed. In this method, since the strain energy generated at the heterointerface is used, processing of the bulk material such as lithography and etching is not required, and the quantum dots are self-formed by a simple process. As an example, a GaAs buffer layer is grown on a GaAs substrate, and an InAs layer having a different lattice constant is grown on the GaAs buffer layer by 1.8 molecular layers, so that a conical growth island (quantum dot) is self-formed ( (For example, refer to Patent Document 1).

  When SK mode growth is used, quantum dots are formed only by crystal growth, so that high-quality crystal dots can be obtained. However, in this method, it is difficult to control the size, position, and density of the quantum dots, and a method for self-forming quantum dots having a uniform size and density using SK mode growth has not yet been realized. Absent.

  On the other hand, a method of forming uniform quantum dots at a high density by a mechanical method without using self-formation has been proposed (see, for example, Patent Document 2).

  In this method, a metal structure having a sharp tip is brought close to the surface of a semiconductor substrate, and an electric pulse is applied to the metal structure to form a fine projection having a diameter and height of several to several tens of nanometers on the surface of the substrate. Form. Thereafter, when an ultra-thin semiconductor film is epitaxially grown on the surface of the substrate including the protrusions, a fine depression is formed immediately above the protrusions. When the quantum dot raw material is supplied to the surface of the ultrathin film having a fine depression, quantum dots are formed only in the depression.

When a scanning tunneling microscope (STM) chip is used, a two-dimensional array of quantum dots can be formed with a repetition period of 50 nm to 100 nn. However, in this method, the substrate must be transferred between the epitaxial growth chamber and the STM processing chamber. When quantum dots are stacked, it is necessary to repeat the reciprocation between the epitaxial growth chamber and the STM processing chamber many times. In addition to the complexity of the quantum dot formation process, there is a concern that the metal chip (cantilever, probe, etc.) may adversely affect the substrate.
Japanese Patent Laid-Open No. 10-289996 JP 2001-7315 A

  InAs quantum dots on a GaAs substrate are expected to be applied to high performance semiconductor lasers (quantum dot lasers) in the optical communication wavelength band. In order to realize a quantum dot laser, it is essential to develop a highly uniform and high density quantum dot manufacturing method. In particular, in order to obtain high-quality crystal dots with high uniformity and high density, development of a self-formation method of quantum dots using the SK growth mode is underway.

  In order to achieve high uniformity in the self-formation of quantum dots, it is important to reduce the growth rate and activate surface migration of growth factors. For this reason, the conditions of the low growth rate were required.

However, under such long surface migration growth conditions, the dot size becomes large, and the density of quantum dots is as low as about 1 × 10 ^{10 to} 3 × 10 ¹⁰ , making it difficult to increase the density.

  Another problem is that if the density of the formed quantum dots is increased, coalescence between the dots occurs.

  Thus, an object of the present invention is to provide a method for forming highly uniform and high-density quantum dots while preventing coalescence between quantum dots.

  Another object of the present invention is to provide a quantum dot laser using such quantum dots.

In order to solve the above problems, in the present invention, when an InAs quantum dot is formed on a GaAs substrate, a GaSb _x As _1-x (0 <x ≦ 1) layer is introduced on the surface of the GaAs layer, InAs quantum dots are self-formed on the GaSb _x As _1-x (0 <x ≦ 1) layer.

As one embodiment, a GaSb layer having a thickness of 0.24 to 1.52 ML, more preferably a single molecular layer is introduced on the surface of the GaAs layer, and InAs quantum dots are formed on the GaSb layer. This is the case of x = 1 with the composition of the GaSb _x As _1-x layer.

In this case, InAs quantum dots are self-formed with a dot density of 1.1 × 10 ¹¹ cm ⁻² or more.

As another embodiment, a GaAsSb mixed crystal buffer layer is introduced on the surface of the GaAs layer, and InAs quantum dots are formed on the GaAsSb mixed crystal buffer layer. This is a case where x ≠ 1 in the composition of the GaSb _x As _1-x layer.

In this case, the InAs quantum dots are self-aligned in a square lattice shape in a predetermined direction within the substrate surface. Further, the dots are uniformly arranged at a high dot density of 1.0 × 10 ¹¹ cm ⁻² or more.

More specifically, the quantum dot formation method is
(A) forming a GaAs buffer layer on the GaAs substrate;
(B) forming a GaSb _x As _1-x (0 <x ≦ 1) layer on the GaAs buffer layer;
(C) InAs quantum dots are self-formed on the GaSb _x As _1-x (0 <x ≦ 1) layer.

  According to this method, by introducing a thin film containing antimony (Sb) on the surface of the GaAs buffer layer, high-density and highly uniform formation of InAs quantum dots is achieved, and coalescence between quantum dots is effectively achieved. Can be suppressed.

Furthermore, the quantum dot forming method described above can be applied to a quantum dot laser. The quantum dot laser includes a GaAs substrate, an active layer on the GaAs substrate, and an electrode for injecting current into the active layer.
(A) a 0.24 to 1.52 ML thick GaSb layer;
(B) InAs quantum dots on the GaSb layer;
(C) a GaAs buried layer for embedding InAs quantum dots;
The InAs quantum dots are arranged at a density of 1.1 × 10 ¹¹ cm ⁻² or more.

  While suppressing the occurrence of coalescence, high-density and highly uniform quantum dots suitable for actual device applications can be self-formed.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic diagram for explaining formation of InAs quantum dots on a GaAs substrate according to the first embodiment of the present invention. In the present invention, InAs quantum dots are formed on a GaSb _x As _1-x (0 <x ≦ 1) layer introduced on the surface of the GaAs buffer layer. In the first embodiment, the composition x of Sb is x = 1 is set, and InAs quantum dots are formed on the GaSb layer.

  FIG. 1A is a schematic diagram of a sample in which InAs quantum dots are formed on a GaSb layer. In this sample, the GaAs buffer layer 2 is formed on the (001) plane of the GaAs substrate 1, the GaSb layer 3 is formed on the surface of the GaAs buffer layer 2, and the InAs quantum dots 4 are self-formed on the GaSb layer 3. can get. The surface arrangement shape of the InAs quantum dots 4 formed in this sample is observed with an AFM (atomic force microscope) as will be described later.

  FIG. 1B is a schematic diagram of a sample in which the InAs quantum dots 4 shown in FIG. 1A are further embedded with a GaAs cap layer 5. As will be described later, the photoluminescence (PL) of the InAs quantum dots 4 is observed using this sample.

  FIG. 2 is a table showing the growth conditions of each layer by molecular beam epitaxy (MBE) when forming InAs quantum dots 4.

First, the GaAs buffer layer 2 is grown on the (001) plane of the GaAs substrate 1 at a growth temperature of 590 ° C. to a thickness of 200 nm. The As pressure at this time is 16 × 10 ⁻⁷ Torr. The pressure value is not an absolute pressure but a value obtained by multiplying a predetermined correction coefficient. The correction coefficient is calculated based on a plurality of factors such as the measurement method, the growth condition, the type of gas material, and the structure of the probe. Similarly, in the following embodiments, the pressure of the supplied substance is indicated by a value multiplied by a correction coefficient.

Next, a GaSb layer 3 of 0.24 to 1.52 ML, preferably 1 ML, is formed on the GaAs buffer layer 2 at a substrate temperature of 500 ° C. and an Sb pressure of 0.5 × 10 ⁻⁷ Torr. At this time, when the film thickness of the GaSb layer 3 is accurately controlled and the surface structure is observed by RHEED, the GaAs-c (4 × 4) diffraction pattern is immediately after the As ₄ irradiation is switched to the Sb ₄ irradiation. It turns out that it gradually changes to a (1 × 3) diffraction pattern, and a rearranged surface of GaSb is formed by the exchange reaction of As and Sb. That is, it is considered that As bonded to Ga on the outermost surface is partially replaced with Sb, and then the entire surface is replaced with Sb to form a GaSb layer having a flat surface.

Next, InAs quantum dots 4 are formed on the GaSb layer 3 by SK mode growth at a substrate temperature of 500 ° C. and a growth rate of 0.035 ML / s. The As pressure at this time is 3 × 10 ⁻⁷ to 8 × 10 ⁻⁷ Torr, preferably 3 × 10 ^{−7 to} 6 × 10 ⁻⁷ Torr. By setting such a growth rate and As pressure low, variations in InAs quantum dot size can be reduced. The growth amount of InAs quantum dots 4 is 2.1 to 3.7 ML.
This state is the state shown in FIG.

After the InAs quantum dots 4 are formed, the substrate temperature is rapidly lowered to 450 ° C., and a GaAs cap layer 5 having a thickness of 100 nm is formed under an As pressure of 6 × 10 ⁻⁷ Torr. This state is the state shown in FIG.

  FIG. 3A is an AFM image obtained from the sample of FIG. In the sample of FIG. 1A, the thickness of the GaSb layer 3 is one molecular layer, and the growth amount of InAs quantum dots is 3 ML. Based on the observation result of AFM, the size and density of InAs quantum dots were evaluated.

By introducing a GaSb layer having a thickness of one molecular layer into the underlying layer of InAs quantum dots, InAs quantum dots with a high density of 1.1 × 10 ¹¹ cm ⁻² are formed. Further, as is clear from the AFM image of FIG. 3A, the InAs quantum dots on the GaSb layer have very high uniformity.

  It should be noted that the occurrence of coalescence is suppressed despite the formation of such a high density. In the observation result obtained in FIG. 3A, there are almost no defects such as dislocation due to the occurrence of coalescence.

  It is known that antimony (Sb) works to lower the surface energy. By inserting a GaSb layer under the InAs quantum dots, the surface is stabilized, and this reduction in energy is considered to affect the surface of the InAs quantum dots from the GaSb / InAs interface. That is, it is considered that coalescence is effectively suppressed by the inactivity of the surface of adjacent InAs quantum dots. This surface stability is considered to contribute to the high uniformity of InAs quantum dots.

  As a comparative example, FIG. 3B and FIG. 3C show AFM images when InAs quantum dots are formed on a GaAs buffer layer as in the prior art without introducing a GaSb layer. FIG. 3B shows a case where a growth rate of 0.035 ML / s InAs quantum dots is formed on the GaAs buffer layer, and FIG. 3C shows the case where InAs is grown on the GaAs buffer layer at a growth rate of 0.17 ML / s. A quantum dot is formed.

As shown in FIG. 3B, surface migration becomes active by setting the growth rate and As pressure low. As a result, the dot size increases, but the size variation decreases. However, the dot density is 2 × 10 ¹⁰ cm ⁻² , and a sufficient density cannot be obtained.

On the other hand, as shown in FIG. 3C, when the growth rate is increased, a relatively high density of 7 × 10 ¹⁰ cm ⁻² can be achieved, but the size variation of InAs quantum dots is remarkable. Furthermore, the occurrence of coalescence is remarkable (2 × 10 ⁹ cm ⁻² ), and many dots enlarged by coalescence (merging) are observed. The dots that have become large due to coalescence have crystal defects, which is a problem in device application.

Thus, in the conventional self-forming method, it is difficult to form high-density and highly uniform quantum dots only by adjusting the growth conditions. However, as in this embodiment, the surface of the GaAs buffer layer is formed. By introducing a GaSb layer having a thickness of about one molecular layer, InAs quantum dots having a uniform size and arrangement interval are formed with high density. At the same time, the occurrence of undesirable coalescence is effectively suppressed, and the practicality of the device is very high.

FIG. 4 shows a planar TEM (transmission electron microscope) image when InAs quantum dots are formed with a growth amount of 3.28 ML on a GaSb layer of one molecular layer thickness at the same substrate temperature, growth rate, and As pressure as described above. It is. Despite a high dot density of 1.1 × 10 ¹¹ cm ⁻² , the occurrence of coalescence is suppressed, and defects such as dislocations are hardly observed.

  Further, as shown in FIGS. 5 and 6, as a result of observation, in the initial stage of growth of InAs on the GaSb layer (growth amount of about 1 ML), a thin line shape having a height of about 0.3 nm (about 1 ML) and a width of about 10 nm. It was found that two-dimensional initial nuclei were formed in a periodic array in the <1-10> direction.

  FIGS. 5A to 5D are AFM images showing the growth process of InAs quantum dots on the surface of the GaSb layer. When InAs is grown on the surface of the GaSb layer by about 1 ML, a thin two-dimensional island starts to be generated, and in 1.4 ML, a very narrow and high-density two-dimensional island is formed as shown in FIG. Is done.

  When InAs is grown to 1.6 ML, the two-dimensional island transitions to a three-dimensional island as shown in FIG. 5C, and when it grows to 3.1 ML, high density and high uniformity are obtained as shown in FIG. InAs quantum dots are formed.

  FIG. 6A is an enlarged image of the InAs two-dimensional island of FIG. Generation | occurrence | production of the elongate linear two-dimensional island arranged periodically and with high density in the <1-10> direction can be confirmed. FIG. 6B is a diagram schematically illustrating a transition from a two-dimensional island to a three-dimensional island. Since the three-dimensional dot grows so as to be trapped on the thin two-dimensional island, it seems that the high-density and highly uniform InAs quantum dots as shown in FIG. 5D are finally formed. . At this time, also in the formation process of InAs three-dimensional quantum dots, the Sb surface segregation effect of the underlayer occurs, and the decrease in surface energy due to Sb atoms in the vicinity of the surface effectively suppresses the generation of coalescence.

  The size and configuration of InAs quantum dots grown on a GaSb layer having a single molecular layer thickness can be controlled by the amount of InAs grown.

FIG. 7 is an AFM image when the amount of growth of InAs quantum dots is changed. FIG. 7A is an AFM image when the InAs coverage (growth amount) is 2.4 ML, and FIG. 7B is an AFM image when the InAs coverage is 3.7 ML. By changing the InAs growth amount from 2.4 to 3.7 ML, the dot density is improved from 7 × 10 ¹⁰ cm ⁻² to 1.1 × 10 ¹¹ cm ⁻² . As is apparent from the AFM image of FIG. 7, the occurrence of coalescence is very small. When the growth amount exceeds 3 ML, the distance between the dots becomes narrow, and as a result, the dot size is almost saturated. That is, a high-density InAs dot with high InAs coverage is expected to suppress size variation.

  For the suppression of size variation, the self-limiting phenomenon due to the stable {110} facets and {136} facets formed on the side walls of the dots plays an important role. In order to observe the facet formation, the RHEED chevron pattern was monitored during SK mode growth of InAs quantum dots on a GaSb layer (GaSb / GaAs) on the GaAs surface.

  FIG. 8 is a RHEED pattern immediately after InAs dots are formed on a GaSb / GaAs layer, and is observed in the <100> direction and the <130> direction. 8A shows the case where the growth amount of InAs quantum dots is 2.4 ML, and FIG. 8B shows the case where the growth amount is 3.7 ML.

  When the InAs coverage is 2.4 ML (FIG. 8A), a RHEED chevron indicating {136} facets in the <130> direction is observed. As the InAs growth increases, {110} facets will also be observed. As shown in FIG. 8 (b), in the 3.7ML coverage, both {136} facets and {110} facets are observed.

  Formation of {110} facets means an increase in dot size and an improvement in dot aspect ratio.

FIG. 9 shows a photoluminescence spectrum (temperature 12K) according to the growth amount of high-density InAs quantum dots on GaSb. When the InAs growth amount is 2.4 ML or less, the width of the PL spectrum is wide and the peak wavelength is in the vicinity of 1100 nm. As the amount of InAs growth increases,
A narrow PL spectrum appears on the long wavelength side (1170 nm). Such dependency of the PL spectrum on the amount of dot growth can be explained by the shape transition of the InAs quantum dots described with reference to FIG.

  That is, the InAs quantum dots that have {110} facets as the growth amount increases, have a peak at 1170 nm on the low energy side. This confirms that as the InAs coverage (growth) progresses, the number of large dot size quantum dots increases. As a result, in a high-density InAs quantum dot formed with a growth amount of 4.1 ML, it can be seen that a relatively narrow peak width of 33 meV can be obtained, and variation in dot size is also suppressed.

As described above, in the first embodiment, by introducing a GaSb layer having a thickness of about one molecular layer on the surface of the GaAs buffer layer on the GaAs (001) substrate, the InAs quantum dots can be made 1.1 with high uniformity. It becomes possible to form at a density of × 10 ¹¹ cm ^-2 or more.

  Furthermore, despite such high density, generation of coalescence can be effectively suppressed, and application to devices is expected.

  FIG. 10 is a schematic configuration diagram of a quantum dot laser to which the above-described high-density and highly uniform InAs quantum dots are applied. In the example of FIG. 10A, the quantum dot laser 10 has an n-type GaAs buffer layer 12, an n-type AlGaAs cladding layer 13, and a GaAs waveguide layer 14 on an n-type GaAs (001) substrate 11. An active layer 15 is provided on the GaAs waveguide layer 14. A GaAs waveguide layer 16 and a p-type AlGaAs cladding layer 17 are located with the active layer 15 in between, and a p-type electrode 19 is provided via an insulating layer (SiO 2 layer) 18 having an opening. On the other hand, an n-type electrode 20 is provided on the back surface of the substrate 11.

As shown in FIG. 10 (b), the active layer 15 was formed on the GaSb layer 21 having a thickness of about one molecular layer and on the GaSb layer 21 with a density of 1.1 × 10 ¹¹ cm ⁻² or more and uniformly. It has InAs quantum dots 22 and a GaAs cap layer 23. The thickness of the GaSb layer 21 can be controlled in the range of 0.24 to 1.52 ML, but a thickness of about one molecular layer is desirable. Although FIG. 10B shows a two-layer stacked structure for convenience, InAs quantum dots 22 self-grown on the GaSb layer 21 may be stacked in three or more layers.

  Unlike the case of forming quantum dots using a probe or cantilever, no matter how many layers are stacked, by controlling the type and amount of supply gas in the same growth chamber, high density and high uniformity InAs quantum Dots can self-form.

  In addition, high-density and highly uniform quantum dots can be easily formed using a commercially available GaAs (001) substrate, which contributes to cost reduction.

Next, a second embodiment of the present invention will be described with reference to FIGS. In the second embodiment, a GaAsSb mixed crystal buffer layer (x ≠ 1) is used as the GaSb _x As _1-x (0 <x ≦ 1) layer on the GaAs buffer layer. In this case, the InAs quantum dots are self-aligned in a square lattice shape in a predetermined direction within the GaAs substrate surface.

FIG. 11 is an AFM image of InAs quantum dots self-aligned on a GaAsSb mixed crystal buffer layer. It can be seen that InAs quantum dots are self-arranged in a uniform square lattice at a high density of 1 × 10 ¹¹ cm ⁻² or more in the <010> direction in the (001) plane of the GaAs substrate.

  FIG. 12 is a schematic diagram for explaining the formation of such a square lattice InAs quantum dot.

After the GaAs buffer layer 32 is grown on the GaAs (001) substrate 31 at 590 ° C.,
A GaAsSb mixed crystal buffer layer 33 is formed in an amount of 10 mL at a growth temperature of 450 ° C. and an As ₄ / Sb ₄ irradiation flux ratio of 3 to 9. The As ₄ / Sb ₄ irradiation flux ratio can be appropriately adjusted in the range of 3 to 9, but as an example, the irradiation flux ratio is set to 6 to form the GaAsSb mixed crystal buffer layer 33, and the GaAs layer 34 is further formed thereon. To form 2ML. An InAs quantum dot 35 is grown on the GaAs layer 34 by 2.6 ML at a growth temperature of 500 ° C.

When the composition of Sb x = 1 as in the first embodiment, that is, when a GaSb layer is introduced, the InAs quantum dots are evenly arranged throughout. In contrast, as in the second embodiment, the Sb configuration x is set to a value other than 1 (0 <x <1), and the film thickness of the GaAsSb mixed crystal buffer layer 33 is set to the As ₄ / Sb ₄ irradiation flux ratio. By appropriately controlling according to the above, it is possible to obtain a square lattice-like quantum dot with the same high density as in the first embodiment. In addition, the uniformity when arranged in a square lattice is also high.

  As described above, in the embodiment of the present invention, when forming an InAs quantum dot, a thin film containing antimony (Sb) is introduced on the surface of the GaAs buffer layer, thereby making it possible to achieve high density and high uniformity of the quantum dot self. Formation can be realized at low cost.

  When forming InAs quantum dots on a GaSb film, generation of coalescence is suppressed, and high-density quantum dots can be obtained in a random uniform arrangement.

  When forming InAs quantum dots on a GaAsSb film, high-density quantum dots can be self-aligned in a uniform square lattice shape.

It is a schematic diagram for demonstrating formation of the quantum dot which concerns on 1st Embodiment of this invention. It is a table | surface which shows the growth conditions of the quantum dot which concerns on 1st Embodiment of this invention. FIG. 3A is an AFM image showing the growth of InAs quantum dots on the GaSb / GaAs layer according to the first embodiment of the present invention. FIGS. 3B and 3C are comparative examples. It is an AFM image when growing an InAs quantum dot on a GaAs buffer layer by a conventional method. It is a TEM image which shows the growth of the InAs quantum dot on the GaSb / GaAs layer which concerns on 1st Embodiment of this invention. FIG. 5A is an AFM image showing the growth of InAs quantum dots on the GaSb / GaAs layer according to the first embodiment of the present invention. FIG. 5A shows an InAs coverage (growth amount) of 2.4 ML, and FIG. ) Is an image when the InAs coverage is 3.7 ML. It is an AFM image showing the growth from an InAs two-dimensional island to a three-dimensional island on GaSb. 7A is an AFM enlarged image of the thin two-dimensional island shown in FIG. 6, and FIG. 7B is a schematic diagram showing a transition from the two-dimensional island to the three-dimensional island. It is a RHEED image immediately after InAs quantum dot formation on the GaSb layer of 1 molecular layer thickness concerning a 1st embodiment of the present invention, and Drawing 8 (a) is 2.4 ML InAs coverage, and Drawing 8 (b) is 3. It is an image at the time of 7ML InAs coverage. It is a graph which shows PL spectrum according to the growth amount of the InAs quantum dot on the GaSb layer of 1 molecular layer thickness concerning a 1st embodiment of the present invention. It is a schematic block diagram of the quantum dot laser to which the quantum dot which concerns on 1st Embodiment of this invention is applied. It is an AFM image of the quantum dot self-alignedly formed on the GaAsSb buffer layer according to the second embodiment of the present invention. It is a schematic diagram for demonstrating formation of the quantum dot which concerns on 2nd Embodiment of this invention.

Explanation of symbols

1, 11, 31 GaAs substrate 2, 12, 32, 34 GaAs buffer layer 3, 21 GaSb layer 4, 22, 35 InAs quantum dots 5, 23 GaAs cap layer 13, 17 AlGaAs cladding layer 14, 16 GaAs optical waveguide layer 15 Active layer 33 GaAsSb mixed crystal buffer layer

Claims (11)

Forming a GaAs buffer layer on the GaAs substrate;
A GaSb _x As _1-x (0 <x ≦ 1) layer is formed on the GaAs buffer layer;
A method of forming a quantum dot, comprising self-forming InAs quantum dots on the GaSb _x As _1-x (0 <x ≦ 1) layer. 2. The quantum dot formation according to claim 1, wherein the GaSb _x As _1-x (0 <x ≦ 1) layer is a GaSb layer (x = 1) having a thickness of 0.24 to 1.52 ML. Method.   The method of forming a quantum dot according to claim 2, wherein the GaSb layer is formed by an As-Sb exchange reaction. The method of forming quantum dots according to claim 2, wherein the InAs quantum dots are self-formed at a dot density of 1.1 × 10 ¹¹ cm ^-2 or more.   3. The quantum dot forming method according to claim 2, wherein the generation of coalescence is suppressed in the InAs quantum dot self-forming step.   The method of forming a quantum dot according to claim 2, wherein the InAs quantum dot is formed with a thin two-dimensional island in the initial growth stage. The GaSb _x As _1-x (0 <x ≦ 1) layer is a GaAsSb mixed crystal buffer layer (x ≠ 1), and the InAs quantum dots are self-aligned in a square lattice shape in a predetermined direction within the substrate surface. The quantum dot forming method according to claim 1, wherein the quantum dots are arranged.   8. The method of forming quantum dots according to claim 7, wherein the InAs quantum dots are arranged in a square lattice pattern along the <010> direction on the (001) substrate plane. The method of forming a quantum dot according to claim 7, wherein the InAs quantum dots are self-aligned in a square lattice pattern with a dot density of 1 × 10 ¹¹ cm ^-2 or more. It said GaAsSb mixed crystal buffer layer, a method of forming the quantum dot of claim 7, wherein the forming in As ₄ / Sb ₄ irradiated flux ratio 3-9. A GaAs substrate;
An active layer on the GaAs substrate;
An electrode for injecting current into the active layer, the active layer comprising:
A GaSb layer having a thickness of 0.24 to 1.52 ML;
InAs quantum dots on the GaSb layer;
A GaAs buried layer for embedding the InAs quantum dots;
And the InAs quantum dots are arranged at a density of 1.1 × 10 ¹¹ cm ⁻² or more.