JPH11340449A - Manufacture of semiconductor quantity dot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly form a quantum dot at the position of a fine thin hole over a wide range. SOLUTION: A fine thin hole 12 is formed on the surface of a semiconductor layer 11 in advance using such nano probe as electron means and STM(scanning- type tunnel microscope), and then a material for terminating the surface of the semiconductor layer 11 is applied for forming a termination film 13 on the surface, and then a quantum dot 14 is formed only on the fine thin hole 12 by the crystal growth method. In this case, when the fine thin hole is to be formed, a surface is generally activated (dangling bond is exposed to the surface). Also, the degree of activation accompanies local nonuniformity, so that a quantum dot may not be formed at a fine thin hole to be formed due to the nonuniform surface diffusion of a growing atom when the crystal growth is made as it is. The present invention has an advantage where the quantum dot 14 is formed uniformly over a wide range at the position of the fine thin hole 12 by terminating the surface with the termination film 13 before the above crystal growth.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method of manufacturing a semiconductor quantum dot whose position and size are finely controlled.

[0002]

2. Description of the Related Art A so-called low-dimensional quantum structure, in which a semiconductor having a narrow band gap is surrounded two-dimensionally or three-dimensionally by a semiconductor having a wide band gap, is used for enhancing the functions and performance of optical and electronic devices. It has been theoretically shown to be promising, and has attracted great interest in recent years as a key to the future development of the optical and electronic industries. In particular, quantum dots having the above-described three-dimensional quantum confinement structure exhibit a wide variety of remarkable quantum effects due to sharpening of the density of states based on strong confinement of electrons. Its realization is expected as a basic structure of a high performance optical / electronic device.

A typical example of a conventionally known method of manufacturing a quantum dot is as shown in FIG. 11A, in which the surface of an epitaxial growth layer 101 on a compound semiconductor substrate 100 is
A mask 102 in which a fine pattern corresponding to the quantum dot size is opened is formed by a lithography technique using an electron beam, an ion beam, a scanning tunneling microscope (STM) or the like, and thereafter, a gas source molecular beam crystal growth (MB)
E) The quantum dots 103 are selectively formed only in the openings by the method or the like.
Have been proposed (eg, Applie
d Physics Letters 68 (1996) 1811). This method has good controllability because the position and size of the manufactured quantum dots can be directly limited by the open area.

However, such a method utilizes a difference in growth rate between a mask portion and a non-mask portion, so that, for example, the substrate 10
0 and the epitaxial growth layer 101 is GaAs, III
The main raw materials for the Group V and Group V materials are organometallic materials that are rich in chemical reactions on the surface, such as trimethylgallium and trimethylindium. In general, since organic metal mainly contains carbon as a main component, the produced crystal contains a large amount of carbon as a raw material, so the crystal quality is not optically good, and it is a serious problem that it cannot be used as a quantum dot. There were drawbacks.

[0005] Another typical method for producing quantum dots using a compound semiconductor is described in, for example, Applied Physics Letters.
63 (1993) 3202, Stransky-Krast
This is a growth method called anov (SK) mode growth. This is because, as shown in FIG. 11B, the so-called strain-based materials 105 and 104 having a different lattice constant from the growth film 101 are formed on the epitaxial growth film 101 on the substrate 100 by a critical film determined depending on the material. In this method, epitaxial growth is performed by a thickness corresponding to a desired thickness. As a result, island-like dots 104 are formed in a self-organizing manner on a thin thin film layer called a wetting rare 105.
Since this method does not require lithography and uses only crystal growth, attention has been paid to high quality crystal dots.

[0006] However, although high quality and relatively uniform size quantum dots can be obtained by this method, it is becoming clear that the formation position and size are insufficiently controlled, and this is a subject to be developed in the future. ing.

[0007] Other typical self-assembly methods known in the art include, for example, Japanese Journal of Applied Physics.
32 (1993) 2052, a method called Volmer-Wever (VW) mode growth as shown in FIG. 11C. This is because if the surface of the epitaxial growth film 101 of the substrate 100 is terminated with an atomic layer film 106 of a material different from that of the growth film 101, then the same material as the growth film 101 is supplied, thereby forming an island-like surface. Dot 107 can be formed. When the substrate is GaAs, the termination atomic film 106 is often made of sulfur (S). This method has an advantage that, unlike the SK mode growth described above, dots of the same material as the surface material are formed in a self-organizing manner.

However, this method also has a drawback in that, similarly to the SK mode growth, the control of the dot formation position and size is insufficient.

In order to overcome such drawbacks, in recent years, stripe-shaped grooves (Applied Physics Letters 66 (1995) 16
20) and micro holes (Applied Physics Letters 68 (199
6) 1684) and tetrahedral grooves (Applied Physics Letters 67)
(1995) 256) and similar techniques are being studied on patterned substrates. In such a method, the pattern is processed by wet etching, and before and after that,
The substrate surface is exposed to air. For this reason, (1) the size of the pattern is several times larger than the quantum dot, the uniformity of which is not good, and (2) the quality of the processed surface on which the dot is formed is oxidized. For these reasons, in the above-described conventional example, there is a limit in realizing high-quality dot formation whose position and size are controlled at the level of atoms and lattices.

A more recent example of solving this problem is a combination of a self-organized crystal growth method and a processing method having a nanometer precision by a focused electron beam or the like, whereby a high-quality position and size are precisely controlled. And attempts to make high-density dots possible (for example, Abstracts of 1
997 Materials Research Society Fall Meeting, Bosto
n, USA, 1997, p.90 or Abstracts of the Fift
h International Workshop on Femtosecond Technolog
y, Tsukuba, Japan 1998, p.88). That is, FIG.
As shown in (d), on the surface of the semiconductor substrate 100 and the epitaxial layer 101 as a buffer layer thereof, a focused electron beam, an ion beam, a scanning tunneling microscope (STM) ) And a fine hole 108 is formed by, for example, a method such as gas etching.
The quantum dot structure 109 is formed only in the processed hole 108 by supplying another semiconductor material called a strain system by the MBE method, which is different from the lattice constant of the semiconductor device 101.

FIG. 12 shows a specific example of this method. In the figure, (a) First, in the MBE room, Ga
And GaAs epitaxial layer 112
Grow. (b) Next, this is transported to an oxidation chamber, and irradiated with halogen lamp light in an oxygen gas atmosphere to form a photo-oxide film mask 113. Next, after evacuating the oxygen gas, (c)
The sample is transferred to an electron beam patterning chamber, and a photo-oxide mask 11
3 A bit matrix pattern 114 having a pitch of, for example, 1 micron is drawn on the upper surface by an electron beam. Next, in the etching chamber, GaAs in the electron beam irradiating portion of the photo-oxide film mask 113 is etched by exposing it to a chlorine gas while the substrate is being heated, for example, having a diameter of 200 to 500 nm and a depth of 50 nm. A minute hole 115 is formed. Next, (e) return to the MBE room again,
By heating at a high temperature under molecular beam irradiation, the photo-oxide film mask on the surface 116 is removed. Then, (f) the substrate temperature is lowered, and again under In molecular beam irradiation, the In molecular beam is supplied for 2 to 3 atomic layers in terms of InAs, thereby selectively forming InAs dots only in the fine holes. Form. Finally, (g) GaAs cap layer 11
8 MBE growth and end the process by embedding InAs dots.

FIG. 11 (ie, FIG. 12) is obtained by the conventional method.
When the InAs dot array is observed with an AFM (atomic force microscope), as shown in FIG. 9B, the InAs dots are formed only at the positions of the micro holes. Further, it has been confirmed by a microscopic surface analyzer (for example, a micro Auger electron spectroscopic analyzer) that no InAs dots are formed except for the fine holes. However, according to this conventional method, the InAs dots are not formed uniformly, as can be seen from the non-uniform shape and size of the white dots indicating the dots in FIG. 9B.

As a cause of such non-uniformity of dots, non-uniformity of the shape, size and depth of the fine holes can be considered. In addition to this, in FIG. It is conceivable that a small amount of unevenness on the flat surface other than the fine holes induced by the residual photo-oxide film mask that was not obtained, or a small amount of unevenness due to the GaAs surface roughness after the removal of the photo-oxide film mask may cause dot nonuniformity. . That is, in the subsequent aggregation process of the InAs dots in (f), the smooth surface diffusion of In or As atoms is hindered by the above-mentioned minute surface irregularities or surface residues, and thus reaches the fine holes.
Since the amount of InAs is non-uniform depending on the location, the shape and size of the obtained InAs dots become non-uniform. Thus, in the conventional example, there is a problem in dot position control and uniformity.

[0014]

The problems imposed on the fabrication of quantum dots that enable high-performance, high-performance optoelectronic devices include high quality (less defects and unnecessary impurities) and high density. It is necessary that the position and size be controlled with good uniformity over a wide range. On the other hand, precise control of the position and size was not sufficient as described above only by the conventional growth method of the SK mode or VW mode. In order to improve this, a conventional example in which a fine pit was previously formed on a substrate, and self-organizing growth by the S-K mode was applied to this, so that dots were selectively formed only in the fine pit. However, as described above, there is a defect that the quality of the dots is deteriorated due to the processing surface being exposed to the atmosphere, and that the uniformity in selectively forming the dots in all the depressions is poor. Was.

An object of the present invention is to provide a method for forming a high-quality quantum dot having a defect-free and precisely controlled position and size with nanometer precision over a wide range and with high uniformity.

[0016]

According to the present invention, a fine depression or projection is formed in advance on the surface of a semiconductor substrate, and the position and the size are precisely adjusted using a material which is the same as or different from the lattice constant of the substrate. When selectively producing controlled quantum dots only in the above-mentioned fine pits or protrusions, by terminating the surface with a terminating film made of a foreign substance before the above-mentioned crystal growth, a wide area can be obtained. To provide a means for uniformly producing quantum dots over a period of time.

That is, according to the present invention, a first step of forming a semiconductor layer made of a first semiconductor having fine depressions or fine projections as a fine pattern on a surface of a substrate; A second step of forming a surface termination film containing the terminating substance on the surface of the semiconductor layer by supplying and decomposing a raw material containing a substance terminating atoms on the surface, and a surface of the surface termination film. Supplying a material made of a second semiconductor to form a quantum dot containing the second semiconductor as a main component only in the surface termination film surface region on the fine pattern. Thus, a method for manufacturing a semiconductor quantum dot is obtained.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to FIGS.

According to the first embodiment of the present invention, a semiconductor layer made of a first semiconductor having fine depressions or fine protrusions (12 or 22) on its surface as a fine pattern on a substrate (10 or 20). The first forming (11 or 21)
And supplying and decomposing a material containing a substance terminating atoms on the surface to the surface of the semiconductor layer to form a surface terminating film (13 or 23) containing the terminating substance on the surface of the semiconductor layer. A second step of forming and supplying a material made of a second semiconductor to the surface of the surface termination film so that the second semiconductor is mainly contained only in the surface termination film surface region on the fine pattern. Quantum dots (14
Or the third step of forming 24) is obtained.

According to a second embodiment of the present invention, in the method of manufacturing a semiconductor quantum dot according to the first embodiment, when the fine pattern is the fine recess, the in-plane dimension of the fine recess is the same as that of the first embodiment. A method for producing a semiconductor quantum dot characterized by not exceeding twice the in-plane dimension of the quantum dot is obtained.

According to a third embodiment of the present invention, in the method of fabricating a semiconductor quantum dot according to the first embodiment, when the fine pattern is the fine protrusion, the in-plane dimension of the fine protrusion is less than the above. A method for producing a semiconductor quantum dot, characterized in that it is not more than the in-plane dimension of the quantum dot, is obtained.

According to a fourth embodiment of the present invention, in the method for fabricating a semiconductor quantum dot according to the first embodiment, wherein the surface of the substrate is a substrate surface composed of a major surface index of a semiconductor, A method for producing a semiconductor quantum dot characterized by having a substrate surface slightly inclined from the index is obtained.

According to a fifth embodiment of the present invention, in the method for fabricating a semiconductor quantum dot according to the first embodiment, the terminating substance is a single atom of sulfur, selenium, tellurium, nitrogen, hydrogen, or These are polyatomic molecules, and the raw materials containing these terminating substances are compounds of hydrogen sulfide, selenium sulfide, tellurium sulfide, nitrogen molecule, ammonia molecule, hydrogen molecule, hydrocarbon molecule, or sulfur, selenium, tellurium alone. According to the present invention, there is provided a method for manufacturing a semiconductor quantum dot.

According to a sixth embodiment of the present invention, in the method for fabricating a semiconductor quantum dot according to the first embodiment, the combination of the second semiconductor and the first semiconductor is mutually strain-free. A method for producing a semiconductor quantum dot, characterized in that it is a strained or strained one, is obtained.

According to a seventh embodiment of the present invention, in the method for fabricating a semiconductor quantum dot according to the sixth embodiment, the combination of the second semiconductor and the first semiconductor is a combination of a strain-free system. In some cases, the combination of the strain-free system of the second semiconductor and the first semiconductor is GaAs / A
lGaAs or In _x Ga _1-x As / InP (x = 0.53) or In _x Ga
_1-x As _y P _1-y /InP(x=0.7,y=0.65) or In _x Ga _1-x As / AlA
_sy Sb _1-y (x = 0.53, y = 0.56) or InP / AlAs _x Sb _1-x (x =
0.56), and when the combination of the second semiconductor and the first semiconductor is a combination of strain systems, the second semiconductor
The combination of the semiconductor and the strain system of the first semiconductor is:
InAs / GaAs, or InGaAs / GaAs, or InP / GaAs, or GaSb / GaAs, or GaAsSb / GaAs, or InGaAs / I
nP or GaAsSb / InP or InP / InAlAs or GaAs
/ GaP, or GaAsP / GaP, or ZeTeSe / ZnSe, or
ZnSe / ZnS, or GaN / AlN, or InAlN / AlN, or
A method for producing semiconductor quantum dots characterized by being InAlN / GaN or SiGe / Si is obtained.

According to an eighth embodiment of the present invention, in the method for fabricating a semiconductor quantum dot according to the first embodiment, the first step is performed by using a focused electron beam, a focused ion beam, a scanning tunneling microscope ( STM), an atomic force microscope (AFM), a processing means using a fine probe, a mask forming means accompanying these as necessary, and a reactive gas introducing means for supporting the processing by the fine probe. Thus, a method for producing a semiconductor quantum dot, which is characterized in that it is obtained, is obtained.

According to a ninth embodiment of the present invention, in the method for fabricating a semiconductor quantum dot according to the first embodiment, the third step is performed by using a molecular beam crystal growth (MBE) method.
According to the present invention, there is provided a method for manufacturing a semiconductor quantum dot, which is performed by using one of a metal organic vapor phase epitaxy (MOVPE) and a liquid phase epitaxy.

According to a tenth embodiment of the present invention, in the method for fabricating a semiconductor quantum dot according to the first embodiment, the first to third steps are performed continuously in a vacuum. Thus, a method for producing a semiconductor quantum dot characterized by the following is obtained.

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a conceptual diagram of the process in the first embodiment of the present invention. In the figure, (a) a fine hole having a size not exceeding twice the size of a target quantum dot is formed on the surface of a semiconductor layer (specifically, an epitaxial growth layer) 11 made of a first semiconductor on a substrate 10. 12 is formed. (b)
On this surface, a surface termination film 13 containing a substance terminating the surface of the semiconductor layer 11 made of the first semiconductor is formed, and thereafter (c)
By supplying an unstrained or strained second semiconductor material to the semiconductor layer 11 made of the first semiconductor, the quantum dots 14 are formed only in the region of the fine holes.
(d) The quantum dots 14 are embedded in the cap layer 15 of the same semiconductor as the semiconductor layer 11 made of the first semiconductor. In the figure,
There are several methods for forming micro holes.
The combination of electron beam irradiation and chlorine gas etching in the conventional example shown in FIG. 2 is one example thereof.

FIG. 2 is a conceptual diagram of the process in the second embodiment of the present invention. In the figure, (a) fine projections 22 having a size equal to or smaller than the size of a target quantum dot are formed on the surface of a semiconductor layer (specifically, an epitaxially grown layer) 21 made of a first semiconductor on a substrate 20. (B) On this surface, a surface termination film 23 containing a substance that terminates the surface of the semiconductor layer 21 made of the first semiconductor is formed, and then (c) the semiconductor layer 21 made of the first semiconductor is strain-free. By supplying a system-based or strain-based second semiconductor material, quantum dots 24 are formed only in the above-mentioned fine projections 22 and finally (d) a semiconductor layer 21 made of the same semiconductor as the first semiconductor layer 21. The quantum dots 24 are embedded in the cap layer 25.

FIG. 3 is a process chart of a specific embodiment in the case of FIG. In FIG. 3, a plurality of processes such as MBE growth and fine electron beam irradiation are performed in a vacuum chamber connected to each other using a complex vacuum apparatus that can be continuously performed.

First, (a) In the MBE room, a GaAs (001) substrate
A Ga molecular beam and an As molecular beam are supplied on 31 and a GaAs epitaxial layer 32 is grown by MBE.

Next, (b) this is transported to an oxidation chamber, and irradiated with halogen lamp light in an oxygen gas atmosphere to form a photo-oxide film mask 33.

Next, after the oxygen gas is evacuated, (c) the sample is transferred to an electron beam patterning chamber, and a bit matrix pattern 34 having a desired shape, for example, a 1 micron pitch, is drawn by an electron beam. At this time, for example, an acceleration voltage, a beam current, and a beam diameter are respectively 20 KeV, 2 nA, and 0.1 μm. The dose of electron beam irradiation is a dose necessary for patterning the photo-oxide film mask, for example, 5 × 10 ¹⁸ electrons / cm ² or more.

Next, (d) a sample is placed in the etching chamber, for example, for 10 minutes.
By heating to 0 ° C and exposing to 2x10 ^-5 Torr of chlorine gas for 30 minutes, GaAs on the electron beam
A fine hole 35 having a depth of 0 to 500 nm and a depth of 50 nm is formed.

(E) Return to the MBE chamber again and heat it to 600 ° C. or more under irradiation of As molecular beam to remove the photo-oxide film mask on the patterned substrate surface 36. Next, (f) stopping the irradiation of the As molecular beam, introducing hydrogen sulfide (H ₂ S) into the room, and irradiating the substrate surface with sulfur vapor generated by thermal decomposition, thereby forming a monoatomic film of sulfur. Form 37.

Next, (g) the substrate temperature is lowered to, for example, 450 ° C., and again under In molecular beam irradiation, an In molecular beam is supplied for 2 to 3 atomic layers in terms of, for example, InAs, and only fine holes are formed. InAs
Is formed. At this time, as the irradiation pressure of the As molecular beam, a high pressure of about 5 × 10 ⁻⁵ Torr or more (twice or more usually used for MBE growth) is used.

Finally, (h) the GaAs cap layer 39 is grown by MBE and the InAs dots are embedded, thereby completing the process.
If desired, these processes can be repeated as many times as desired, and lamination is possible.

The process of forming the surface terminating film in FIGS. 1 (b), 2 (b) and 3 (f) is the main part of the present invention. The process of forming the termination film will be described in detail.

In FIG. 4A, the surface of the first semiconductor epitaxial crystal layer 41 is activated by the process of forming the fine holes 44, and the unpaired electron coupler 42, so-called, A large amount of dangling-bonds are left unterminated. Such unpaired electronic connectors are further increased when the surface includes irregularities at the atomic layer level induced by various processes. Such a surface has a high energy, and therefore has a strong tendency to adsorb and accumulate atoms and molecules from the outside.

In this state, as shown in FIG. 4A, when the surface is covered with a film 43 capable of terminating the bond 42, the unpaired electron coupler 42 is no longer exposed to the surface. Therefore, when the atoms 46 constituting the quantum dots are irradiated, they move on the surface over a distance (surface diffusion length) determined by the temperature and other conditions. At this time, the atoms 46 Is easy to move around freely, and thus it is easy to reach the periodic fine holes 44 uniformly. Therefore, uniform quantum dots are formed in the fine holes. Here, the inside of the fine hole will be described. Although the terminal film 45 is bonded to the bond even in the fine hole as shown in the figure, the number of bonds is larger than that of the flat surface because a higher-order crystal plane is exposed on the wall surface of the fine hole. For this reason, surplus bonds not terminated by the termination film 45 remain. Therefore, the surface energy of the inside of the fine hole is higher than that of the outer terminal surface. Further, since the higher-order surface is exposed on the wall surface of the fine hole, there are many atomic layer steps. From this, the surface energy inside the fine hole is higher than that at the outer terminal surface. For these reasons, the atoms 46 are more easily taken into the fine holes 44 than the surroundings. Therefore, the atoms 46 are deposited in the fine holes 44 to form dots even though the termination film 45 exists. When the constituent atoms 46 of the dot are so-called strain-based materials having a lattice constant different from that of the surface layer 41, the selectivity for growing the dot into a fine hole with respect to the flat surface is remarkable, but the lattice constant Even in the case of an equal so-called strain-free system, dot-like growth occurs similarly with the decrease in the selectivity.

FIG. 4A illustrates the case where the terminating film 45 also covers the inner surface of the fine hole 44. However, when quantum dots are formed thereon while the terminating film 45 remains, For application to devices and the like, the light emission characteristics may be reduced.
In such a case, as shown in FIG. 4 (b), the substrate temperature is slightly increased after the termination film 45 is attached, and the The inner wall 49 can be formed. In this case, the quantum dots composed of the atoms 46 become high-quality microcrystals as compared with the case of FIG.

FIGS. 5A and 5B show the operation of the present invention when forming quantum dots using the fine projections shown in FIG.

That is, in FIG. 5 (a), the surface of the first semiconductor epitaxial crystal layer 51 is activated by the pattern formation process of the fine projections 54, whereby the surface atomic plane is activated, and the unpaired electron coupling occurs. The child 52 exists in large quantities without being terminated. Such unpaired electronic connectors are further increased when the surface includes irregularities at the atomic layer level induced by various processes. Such a surface has a high energy, and therefore has a strong tendency to adsorb and accumulate atoms and molecules from the outside. Here, FIG.
As shown in (a), a film that can terminate the bond 52 of the crystal layer 51
When the surface is covered with 53, the unpaired electron coupler 52 is no longer exposed to the surface. Therefore, when the constituent atoms 56 of the quantum dot are irradiated, they move on the surface over a distance (surface diffusion length) determined by the temperature and other conditions.
Is easy to move around the surface freely as compared with the case where the terminal film 53 is not provided, and thus it is easy to reach the periodic fine holes 54 uniformly. Therefore, uniform quantum dots are formed on the fine protrusions. Although the termination film 55 is bonded to the bond on the wall surface of the fine protrusion 54 as shown in the figure, the number of bonds is larger than that of the flat surface because the higher-order crystal plane is exposed on the wall surface of the fine protrusion. . For this reason, surplus bonds not terminated by the termination film 55 remain. Therefore, the surface energy of the inside of the fine protrusion is higher than that of the outer terminal surface. Further, since the higher order surface is exposed on the wall surface of the fine projection, there are many atomic layer steps. Therefore, the surface energy of the inside of the fine projection is higher than that of the outer terminal surface. For these reasons, the fine projections 54 are more likely to take in the atoms 56 than the surroundings. Therefore, the atoms 56 are deposited on the fine projections 54 to form dots even though the termination film 55 is present. Note that when the constituent atoms 56 of the dot are so-called strain-based materials having a different lattice constant from the surface layer 51, the selectivity to grow in the form of a dot in a fine hole with respect to the flat surface described above is remarkable. Even in the case of an equal so-called strain-free system, although the selectivity is reduced, the dot-like growth occurs similarly to the case where the fine holes are used.

FIG. 5A illustrates the case where the terminating film 55 also covers the surface of the fine protrusion 54. However, when the quantum dots are formed on the terminating film 55 while the terminating film 55 remains, Similarly,
When applied to an optical element or the like, the light emission characteristics may be reduced. In such a case, as shown in FIG. 5 (b), as compared with the case of FIG. Is formed. In this case, the quantum dots composed of the atoms 56 become higher quality microcrystals.

FIG. 6 shows another embodiment in which fine holes are formed in the surface of the semiconductor layer made of the first semiconductor. In the first embodiment of FIG. 3, electron beam lithography and gas etching are continuously performed under vacuum to form fine holes, but in this embodiment, the tip 62 of the STM (scanning tunneling microscope) chip is connected to the semiconductor surface layer. A constituent element of the surface layer 61 is desorbed by causing a tunnel voltage to flow between the semiconductor layer and the semiconductor surface by applying a desired voltage to the semiconductor layer 61 so as to form a fine hole 63. According to this method, it is easy to form a fine hole having a diameter equal to or smaller than the quantum dot diameter (about 10 nm).

FIG. 7 shows another embodiment in which fine projections are formed on the surface of the semiconductor layer made of the first semiconductor. The fine projections 22 in FIG. 2A can be formed by using electron beam lithography and gas etching as in the case of forming the fine holes in FIG. A chip similar to the STM is brought near the surface 71. A melt 73 of a substance to be fine projections 74 adheres to the surface of the chip, and adheres to the surface as fine projections 74 by electric field evaporation from the tip 72 of the chip. The fine projections 74 thus obtained contribute to the subsequent nucleation of quantum dots.

FIG. 8 shows another embodiment of the preparation of an atomic film for terminating the surface of the semiconductor layer made of the first semiconductor. In the embodiment shown in FIG. 3, the sulfur monoatomic film of (f) is used.
37 is formed by introducing hydrogen sulfide (H ₂ S) into the sample chamber, passing it through a group of tungsten filaments heated at a high temperature, and thermally decomposing to produce atomic sulfur, which is irradiated onto the sample surface It was done by In contrast, FIG.
Then, the hydrogen sulfide (H
₂ S) is decomposed to atomic sulfur by plasma discharge, i.e. becomes sulfur radical, consist small hole provided on the sample side with sulfur radical beam 83 is irradiated on the surface of the epitaxial growth layer 81 grown on the substrate 80 You. The method is illustrated in FIG.
The decomposition efficiency is good because it is decomposed by the plasma in a high energy state as compared with the thermal decomposition of (f), so that a large amount of sulfur radicals are irradiated to the sample, so that the desired coverage with good coverage can be obtained in a short time. There is an advantage that an atomic film can be formed.

Next, a modification of the present invention will be described.

1. In the embodiment of the present invention, the fine hole diameter is 200-5
Since a patterned substrate with a size of 00 nm and an array period of about 1 micron was used, the position control was good, but the dot size was large, 100-200 nm, and the uniformity was 10 μm.
%. However, if the size of the microholes or microprotrusions and the period of the arrangement are very small, it is possible to make the size of the dots as small as about 10 nm, and at this time, the controllability of the position and size is improved. When fabricating high-density quantum dots with a size of 10 nm and an array period of about 30 nm, the upper limit of the required in-plane size of the microholes or protrusions should not exceed twice the in-plane size of the dots. desirable. This is because the adjacent minute holes or minute projections do not overlap. At this time, the lower limit of the in-plane size of the fine hole or the fine protrusion is not limited by a principle factor, but the present invention is effective even at about 2-3 nm.

2. In the embodiment of the present invention, sulfur is used as a film material for terminating the surface of the first semiconductor layer. However, other materials such as selenium, tellurium, nitrogen, hydrogen and unsaturated compounds containing these are also used. It is valid. Further, any substance having a function of terminating an unpaired electron connector on the substrate surface and inactivating the surface is effective.

3. In the embodiment of the present invention, GaAs is used as the substrate.
Although the (100) substrate is used, other substrate surfaces such as the (111) A substrate and the (110) substrate, or their slightly inclined substrate surfaces are also effective.

4. In the embodiment of the present invention, as a combination of the second semiconductor forming the quantum dot and the first semiconductor surrounding the quantum dot, a system having different lattice constants from each other is used.
In other words, the strain system InAs / GaAs was used, but other strain systems,
That is, InGaAs / GaAs, InP / GaAs, GaSb / GaAs, GaAs
Sb / GaAs, InGaAs / InP, GaAsSb / InP, InP / InAlAs, GaAs
/ GaP, GaAsP / GaP, ZeTeSe / ZnSe, ZnSe / ZnS, GaN / AlN
, InAlN / AlN, InAlN / GaN, and SiGe / Si are also effective in the present invention. Furthermore, not only a strain system as the combination, but also a strain-free system having the same lattice constant as each other, that is,
GaAs / AlGaAs, In _x Ga _1-x As / InP (x = 0.53), In _x Ga _1-x As _y P
_1-y /InP(x=0.7,y=0.65), In _x Ga _1-x As / AlAs _y Sb _1-y (x = 0.
53, y = 0.56), the combination of InP / AlAs _x Sb _1-x (x = 0.56) is also effective, and the present invention is effective for all combinations of strain systems other than the above and strain-free systems. .

5. In the embodiment of the present invention, a combination of an electron beam and gas etching is used as a means for forming a fine hole on the first semiconductor surface. Ion beam, STM
In addition to the chip being effective, the tip of the hollow optical fiber is sharpened, a reactive gas flows into the hollow, and the gas released from the tip is released to the substrate,
Means in which minute holes are formed in the substrate are also effective in the present invention.

6. In the embodiment of the present invention, molecular beam crystal growth (MBE) was used as a crystal growth method, but any other semiconductors such as metal organic chemical vapor deposition (MOVPE) and liquid phase growth may be used. All epitaxial growth methods are effective for the present invention.

[0057]

As described above, according to the present invention, fine holes or fine protrusions are previously formed by electron beams or the like at positions where quantum dots are to be formed on the surface of the semiconductor layer made of the first semiconductor on the substrate. A pattern is formed, and thereafter, the patterned surface is terminated with a film of a desired material, and a second semiconductor material that is the same as or different from the first semiconductor is supplied, thereby forming the fine holes or fine protrusions. Microcrystals mainly composed of the second semiconductor material can be formed only in the vicinity, and can be used as quantum dots. In this case, as described with reference to FIG. 4 and FIG. 5, according to the present invention, high-quality and high-density dots whose positions are precisely controlled can be produced uniformly over a wide range. Also,
When the fine holes or fine protrusions are periodically arranged, the supplied atoms of the second semiconductor are uniformly and uniformly diffused on the surface termination film to reach the fine holes or fine protrusions. Therefore, the variation in the size of the obtained quantum dots is suppressed as compared with the conventional case. In addition, since all of these processes are performed consistently in a vacuum, high-quality products can be obtained, and at the same time, they can be repeated, so that lamination is easy.

In order to clearly show the effects of the present invention described above,
9 and 10 show the results based on the examples. FIG.
(a) shows InAs formed only in the periodic holes formed on the GaAs substrate according to the embodiment of the present invention shown in FIG.
It is an AFM (atomic force microscope) image of a dot arrangement. The figure shows the case where micro holes are arranged at a pitch of 1 micron.
This is an example of producing a 1 micron diameter dot. FIG.
9 is an AFM image showing a similar InAs dot production example obtained by the second conventional example. In FIG. 2B, the uniformity of the InAs dots (white spots) is poor, whereas in FIG. 2A of the present invention, the InAs dots are formed with high uniformity over a wide area. I understand.

FIG. 10 is an AFM image of an experiment supporting the effect of the embodiment of the present invention shown in FIG. Figures (a) and (b)
Using a flat GaAs substrate on which neither fine holes nor fine protrusions are formed, the A
It is an FM image. However, in this case, the flat substrate is previously divided into 50-micron square patterns by one side by mesa etching. In the figure, (a)
After forming the surface termination film of sulfur used in the present invention, InAs
Is the surface on which MBE growth of
As dots are not formed at all. The irradiated InAs
Because there are no fine holes or fine protrusions for dot nucleation,
The surface on which the termination film is formed is rapidly diffused, and is eliminated and deposited outside the square pattern. On the other hand, (b) of the figure shows that, because there is no surface terminating film, even if the surface has no microholes or microprojections, it is trapped by the unpaired electron couple, and as a result, as shown by the arrow, the conventional type InAs dots formed in the SK mode growth of which the positions and sizes are non-uniform are formed. This experiment also suggests that the presence of the surface termination film contributes to the uniform InAs dot formation shown in FIG. 9A.

[Brief description of the drawings]

FIG. 1 is a process conceptual diagram of a method for manufacturing a semiconductor quantum dot according to a first embodiment of the present invention.

FIG. 2 is a process conceptual diagram of a method for manufacturing a semiconductor quantum dot according to a second embodiment of the present invention.

FIG. 3 is a specific process chart in the embodiment of FIG. 1;

FIG. 4 is a diagram for explaining the function of the surface termination of the surface termination film used in the present invention.

FIG. 5 is a diagram for explaining another function of the surface termination of the surface termination film used in the present invention.

FIG. 6 is a structural cross-sectional view for explaining another method for producing a fine hole (fine depression) of the present invention.

FIG. 7 is a structural cross-sectional view for explaining another method for producing a fine projection of the present invention.

FIG. 8 is a structural sectional view showing another method for forming the surface termination film of the present invention.

FIG. 9 is a photomicrograph showing an atomic force microscope (AFM) image of an experimental result showing the effect of homogenizing quantum dots according to the present invention (a) as compared with the conventional example (b).

FIG. 10 is a micrograph showing an AFM image of an experimental result supporting the surface termination effect according to the present invention of FIG. 9;

FIG. 11 is a conceptual diagram of a process of manufacturing a quantum dot according to a conventional example.

FIG. 12 is a specific process chart in the conventional example of FIG. 11;

[Explanation of symbols]

 10 Substrate 11 Semiconductor layer 12 Micro hole 13 Surface termination film 14 Quantum dot 15 Cap layer 20 Substrate 21 Semiconductor layer 22 Micro projection 23 Surface termination film 24 Quantum dot 25 Cap layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyoshi Asakawa 5-7-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation (72) Inventor Tomonori Ishikawa 5-5-1 Tokodai, Tsukuba City, Ibaraki Prefecture Femtosecond Technology Research Institute

Claims (10)

[Claims] 1. A semiconductor layer (11 or 2) made of a first semiconductor having fine depressions or fine projections (12 or 22) on its surface as a fine pattern on a substrate (10 or 20).
A first step of forming 1); and supplying and decomposing a raw material containing a substance terminating atoms on the surface to the surface of the semiconductor layer to form a surface terminating film (13 or 23) containing the terminating substance. Forming a second semiconductor material on the surface of the semiconductor layer, and supplying a material made of a second semiconductor to the surface of the surface termination film, so that only the surface termination film surface region on the fine pattern is Forming a quantum dot (14 or 24) containing a second semiconductor as a main component. 2. The method of manufacturing a semiconductor quantum dot according to claim 1, wherein when the fine pattern is the fine depression, an in-plane dimension of the fine depression exceeds twice an in-plane dimension of the quantum dot. A method for manufacturing a semiconductor quantum dot. 3. The method of manufacturing a semiconductor quantum dot according to claim 1, wherein when the fine pattern is the fine projection, an in-plane dimension of the fine projection is equal to or less than an in-plane dimension of the quantum dot. Characteristic method of manufacturing semiconductor quantum dots. 4. The method of manufacturing a semiconductor quantum dot according to claim 1, wherein the surface of the substrate is a substrate surface composed of a main surface index of the semiconductor or a substrate surface slightly inclined from the surface index. Characteristic method of manufacturing semiconductor quantum dots. 5. The method according to claim 1, wherein the terminating substance is sulfur, selenium,
Tellurium, nitrogen, a single atom of hydrogen, or a polyatomic molecule containing these, the raw material containing these terminating substances, hydrogen sulfide,
Selenium sulfide, tellurium sulfide, nitrogen molecule, ammonia molecule,
Hydrogen molecules, compounds of hydrocarbon molecules, or sulfur, selenium,
A method for manufacturing a semiconductor quantum dot, which is a single element of tellurium. 6. The method of manufacturing a semiconductor quantum dot according to claim 1, wherein a combination of the second semiconductor and the first semiconductor is a strain-free system or a strain-based system. Of producing semiconductor quantum dots. 7. The method of manufacturing a semiconductor quantum dot according to claim 6, wherein the combination of the second semiconductor and the first semiconductor is a strain-free combination. The combination of the strain-free system of semiconductor 1 is GaAs / AlGaAs, or In _x Ga _1-x As / InP (x = 0.53), or
In _x Ga _1-x As _y P _1-y /InP(x=0.7,y=0.65) or In _x Ga _1-x A
s / AlA _sy Sb _1-y (x = 0.53, y = 0.56) or InP / AlAs _x Sb
_1-x (x = 0.56), and when the combination of the second semiconductor and the first semiconductor is a combination of strain systems, the combination of the second semiconductor and the strain system of the first semiconductor is , InAs / GaAs, or InGaAs / GaAs, or InP / GaAs, or GaSb / GaAs, or GaAsSb / GaAs, or InGaAs / I
nP or GaAsSb / InP or InP / InAlAs or GaAs
/ GaP, or GaAsP / GaP, or ZeTeSe / ZnSe, or
ZnSe / ZnS, or GaN / AlN, or InAlN / AlN, or
A method for producing a semiconductor quantum dot, wherein the semiconductor quantum dot is InAlN / GaN or SiGe / Si. 8. The method of manufacturing a semiconductor quantum dot according to claim 1, wherein the first step is performed using a focused electron beam, a focused ion beam, a scanning tunneling microscope (STM), or an atomic force microscope (AFM). A method for manufacturing a semiconductor quantum dot, wherein the method is performed by processing with any one of fine probes. 9. The method of manufacturing a semiconductor quantum dot according to claim 1, wherein the third step is performed using a molecular beam crystal growth method (MBE), a metal organic chemical vapor deposition method (MOVPE), or a liquid phase growth method. A method for manufacturing a semiconductor quantum dot, which is performed by using any one of the methods. 10. The method of manufacturing a semiconductor quantum dot according to claim 1, wherein the first to third steps are continuously performed in a vacuum.