JP2003109976A - Sb2Te3 SINGLE-CRYSTAL THIN FILM AND METHOD OF MANUFACTURING THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Sb2 Te3 single-crystal thin film which can be manufactured simply and at low costs by using a molecular beam epitaxy method, and to provide a method of manufacturing the single-crystal thin film. SOLUTION: In the method of manufacturing the Sb2 Te3 single-crystal thin film, an Sb2 Te3 epitaxial single crystal is grown on a substrate arranged inside an airtightly sealed vacuum container 1. The method of manufacturing the Sb2 Te3 single-crystal thin film comprises a buffer growth step wherein the Sb2 Te3 epitaxial single crystal is deposited on the substrate at a substrate temperature at which a Bi2 Te3 vapor pressure becomes smaller than a pressure inside the container 1; an annealing step wherein the substrate temperature is raised up to a temperature at which the Bi2 Te3 vapor pressure becomes larger than the pressure inside the container 1, and the substrate temperature is decreased down to a temperature at which the Bi2 Te3 vapor pressure becomes smaller than the pressure inside the container 1; and a crystal growth step in which the Sb2 Te3 single crystal is grown on the surface of the Sb2 Te3 epitaxial single crystal grown In the steps.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Sb ₂ Te ₃ single crystal used for a Peltier device for realizing a solid state air conditioner, a thermoelectric power generation device used for recovering exhaust heat energy, and a thermoelectric conversion device such as a temperature sensor. A thin film and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, environmental problems have become very important, and it is desired to reduce the use of CFCs in air conditioners and coolers and to save energy by improving heat exchange efficiency. The thermoelectric conversion element is promising as a reversible direct conversion element of heat energy and electric energy, but it has not been widely spread because of its low conversion efficiency. As a method to improve the conversion efficiency of a thermoelectric conversion element, a quantum well structure in which an extremely thin film with a thickness of several tens of liters is formed with a thermoelectric conversion material and the film is sandwiched with a material with a bandgap width wider than this film is effective. LD Hicks and others have made this clear.

This technology is based on LDHicks and MS Dresselh.
aus, “Effect of quantum-well structures on the the
rmoelectric figure of merit ”, Phys. Rev. B 47,19, pp.
It is published in the document 12727-12731 (1993). Bi ₂ T, which is a typical thermoelectric conversion material used near room temperature
In order to realize a quantum well structure with e ₃ , it is necessary to select a suitable material for the barrier layer sandwiching the quantum well layer Bi ₂ Te ₃ . In order to laminate an extremely thin film in multiple layers, each layer must be a single crystal layer that is flat at the atomic level, and epitaxial single crystal growth is performed to grow the upper layer crystal reflecting the crystal structure of the underlayer. Sb ₂ Te ₃ belong to the same crystal system as Bi ₂ Te _3, because it has a very close lattice constant Bi ₂ Te _3, is a promising material as a barrier layer.

Usually, in order to grow a single crystal film on a substrate, it is necessary to select a substrate whose crystal structure and lattice constant are close to those of the target product to be grown. Sb ₂ Te ₃
In the case of growing a single crystal film, a sapphire (Al ₂ O ₃ ) substrate can be mentioned as a substrate having a crystal structure and a lattice constant that are close to Sb ₂ Te ₃ . However, even on the lattice plane (0001) plane of this sapphire (Al ₂ O ₃ ) substrate, molecular beam epitaxy (M
olecular Beam Epitaxy: MBE) in the apparatus, Sb ₂ Te ₃ Attempting to grow directly Sb ₂ Te ₃ on the sapphire substrate because results in polycrystalline growth, growing a Sb ₂ Te ₃ single crystal film on a sapphire substrate It was difficult to do.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and makes it possible to grow a Sb ₂ Te ₃ single crystal film on a substrate at a simple and inexpensive cost by using a molecular beam epitaxy method. An object is to provide an Sb ₂ Te ₃ single crystal thin film and a method for manufacturing the same.

[0006]

Means for Solving the Problems Sb according to the present invention₂Te₃Single bond
Crystal thin film manufacturing method, the substrate placed in a closed container
Sb on₂Te₃Sb to grow epitaxial single crystal₂Te₃single
A method of manufacturing a crystalline thin film, comprising:₂Te₃Vapor pressure is in the container
At substrate temperature less than the internal pressure, Bi₂Te₃On the board
Buffer growth stage to deposit on Bi,₂Te₃Vapor pressure is above
Raise the substrate temperature to a temperature above the pressure inside the container.
After raising it, Bi₂Te₃The vapor pressure is higher than the pressure in the container.
Annealing that lowers the substrate temperature to a temperature that is less than
Stage and these buffer growth and annealing stages
Therefore Bi grown on the substrate ₂Te₃Epitaxial single
On the surface of the crystal, Sb₂Te₃Crystal growth stage to grow single crystal
It is a method including and.

Although the substrate is not particularly limited,
Sb ₂ Te ₃ single crystal sapphire (Al ₂ O ₃ ) having a relatively close crystal structure and lattice constant is preferable. However, as described above, the lattice constants of the sapphire substrate to slightly different and Sb ₂ Te ₃ single crystal, it is difficult to grow directly Sb ₂ Te ₃ single crystal sapphire substrate. According to the invention, Bi
_{By using the 2} Te ₃ single crystal thin film as a buffer layer of the substrate and the Sb ₂ Te ₃ single crystal thin film, a good quality Sb ₂ Te ₃ single crystal thin film can be produced.

The pressure in the container is not particularly limited, but is preferably in the range of 10 ^-6 to 10 ^-8 Pa, for example. The buffer growth step and the annealing step may each be performed once, but it is preferable to repeat the buffer growth step a plurality of times, for example, twice in order to form a stable thin film. The processing time of the buffer growth stage is preferably
It is 5 to 120 seconds, and more preferably 10 to 60 seconds. The processing time of the annealing step is 1 to 10
Minutes, more preferably 3 to 5 minutes.

Further, in one embodiment of the method for producing a Sb ₂ Te ₃ single crystal thin film according to the present invention, in the buffer growth stage,
It is a method of depositing Bi ₂ Te ₃ on a substrate by generating Bi molecular beam and Te molecular beam and irradiating on the substrate. Furthermore, in another aspect of the method for producing a Sb ₂ Te ₃ single crystal thin film according to the present invention, in the crystal growth step, Sb molecular beams and Te molecular beams are generated to form a surface of the Bi ₂ Te ₃ epitaxial single crystal. This is a method of growing an Sb ₂ Te ₃ single crystal by irradiation.

As described above, as a method of depositing Bi ₂ Te ₃ on a substrate or a method of growing an Sb ₂ Te ₃ single crystal thin film on the surface of a Bi ₂ Te ₃ single crystal, a general apparatus that does not require a special device is used. By using the molecular beam epitaxy method, a Sb ₂ Te ₃ single crystal thin film can be prepared easily and at low cost.
Then, in still another aspect of the method for producing a Sb ₂ Te ₃ single crystal thin film according to the present invention, the Bi molecular beam, the Te molecular beam and the Sb molecular beam are generated by a molecular beam epitaxy method, and the molecular beam epitaxy is performed. The temperature conditions in the method are 550 to 570 ° C for Bi source, 310 to 330 ° C for Te source and S
b source is 450 to 470 ° C, and substrate surface is 255 to
This is a method of setting the temperature to 275 ° C. By performing the molecular beam epitaxy method under the above-mentioned temperature condition, a good quality Sb ₂ Te ₃ single crystal thin film can be obtained, and conversely, if it goes out of these temperature ranges, it becomes polycrystalline.

The Sb ₂ Te ₃ single crystal thin film according to the present invention is
It is a thin film manufactured by the method described above. By the general molecular beam epitaxy method for growing single crystal thin film
Since an Sb ₂ Te ₃ epitaxial single crystal thin film can be produced, it can be performed easily and at low cost without requiring a special device or the like.

The thermoelectric conversion element according to the present invention is a thermoelectric conversion element using the Sb ₂ Te ₃ single crystal thin film. The thermoelectric conversion element reversibly directly converts thermal energy and electric energy, and includes a Peltier element used in a solid state air conditioner, a thermoelectric power generation element used to recover exhaust heat energy, and a temperature sensor.
In the present invention, a substrate, a Bi ₂ Te ₃ single crystal buffer layer grown on the substrate, and an Sb ₂ Te ₃ single crystal thin film grown on the Bi ₂ Te ₃ single crystal buffer layer. The provided thermoelectric conversion material can be obtained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The Sb ₂ Te ₃ single crystal thin film and the method for producing the same according to the embodiments of the present invention will be described in detail below with reference to the drawings. In this embodiment, an example of producing a Sb ₂ Te ₃ epitaxial single crystal thin film on a sapphire substrate through a Bi ₂ Te ₃ epitaxial single crystal thin film using a molecular beam epitaxy method (hereinafter referred to as MBE method) Will be described.

[Molecular Beam Epitaxy Device] The structure of a molecular beam epitaxy device (hereinafter referred to as MBE device) used in the present invention is schematically shown in FIG.

The MBE device 20 is shut off from the outside by the vacuum container 1, and the inside is kept at a predetermined pressure of 10 ^-7 Pa or less (for example, 10 ^-8 Pa). The vacuum container 1 is connected to a high vacuum evacuation unit (not shown) such as a turbo molecular pump or a cryopump through an exhaust duct 2, and the substrate 3 for growing a target thin film is a substrate. It is held by the holder 4. The substrate holder 4 is provided with a heating unit and a temperature adjusting function, which are not shown, so that the temperature of the substrate 3 can be maintained at an arbitrary set temperature.

In addition, K cells (Knudsen Cell) 8a, 8b,
8c is arranged toward the substrate 3, and crucibles 9a, 9b, 9c, heaters 10a, 10 are provided in the K cell.
b, 10c and shutters 11a, 11 that can be opened and closed
b and 11c are provided. Bi (bismuth) source 5, Sb (antimony) source 6, and Te (tellurium) source 7 are filled in the crucibles 9a to 9c in the K cells 8a to 8c, and the source heaters 10a to 10c.
It is configured to be heated by c.

When the sources 5 to 7 are heated by the source heaters 10a to 10c, they evaporate, and the molecular beams 2
2a, 22b and 22c, which reach the surface of the substrate 3 without colliding with the residual gas molecules in the vacuum container 1 and serve as a material supply source for thin film growth. Then, the shutter 11
By controlling the opening and closing of a to 11c, the element can be selectively supplied to the surface of the substrate 3 and a desired composition material can be grown.

Further, on the upper side wall of the vacuum container 1, a reflection high energy electron diffraction (Reflection High Energy Electron Dif
An electron gun 12a and a RHEED screen 12b are arranged facing the electron gun 12a. The growth of the thin film is performed by the RHEED image on the substrate 3
The upper growth surface can be observed in real time. RHEED
When the surface of the substrate 3 is irradiated with the electron beam 21 from the electron gun 12a at an angle of 2 to 3 °, the fluorescent surface coated on the back surface of the RHEED screen 12b is irradiated with the reflected electron beam 21 containing the crystal structure information of the growth surface. To be done. By observing this fluorescence pattern, it is possible to know the state of the crystal surface growing on the substrate 3. A vacuum degree measuring means 13 for measuring the degree of vacuum inside the vacuum vessel 1 is provided at the upper end of the vacuum vessel 1. As the vacuum degree measuring means 13, for example, an ionization vacuum gauge or the like is preferably used.

[Substrate] As described above, as the substrate 3, a single crystal having a crystal structure close to that of the target product to be epitaxially grown is used. The target product Sb ₂ Te ₃ single crystal in the present invention belongs to a trigonal system as shown in FIG. 2, and a ₀ = 4.262Å,
It has a lattice constant of c ₀ = 30.450Å. Considering crystal growth in the c-axis direction, it is desirable that the substrate 3 is a trigonal crystal or a hexagonal crystal having the same crystal system, and a material having a lattice constant a ₀ in the c (0001) plane is close. In addition to this, considering physical factors such as material availability and surface polishability, a sapphire single crystal having a trigonal crystal structure with a ₀ relatively close to lattice constants a ₀ = 4.763Å and c ₀ = 13.003Å preferable. But Sb ₂
Since the difference in a ₀ between the Te ₃ single crystal and sapphire is 11.8%, strain will occur at the heterojunction interface between the two.
It becomes an obstacle to the growth of a good quality single crystal.

Here, even if an attempt was made to grow Sb ₂ Te ₃ directly on a sapphire substrate by the molecular beam epitaxy method under various source temperatures and substrate temperature conditions, it was found that Sb ₂ Te ₃ was randomly oriented. It becomes a crystal and an epitaxial single crystal cannot be obtained. On the other hand, Bi ₂ Te ₃ single crystal is a trigonal system with a ₀ = 4.3852Å, c ₀ = 30.483Å and Sb ₂ Te ₃
Has a lattice constant very close to, and a ₀ (Sb ₂ Te ₃ ) <
The condition of a ₀ (Bi ₂ Te ₃ ) <a ₀ (sapphire) is satisfied. Therefore, Bi ₂ Te ₃ single crystal and Sb
_The present inventors have paid attention to alleviating the mismatch in the lattice constant between sapphire and Sb ₂ Te _{3 by} using it as a buffer layer between the ₂ Te ₃ single crystal.

[Vapor Pressure] FIG. 3 shows a source source.
Bi, Te, Sb, and the target product Bi₂Te₃And Sb ₂Te₃Steam of
It is a barometric pressure curve. MBE equipment is 10^-7Predetermined below Pa
Source 5 against the back pressure in the vacuum vessel set to pressure
By heating ~ 7, a molecular beam is generated by evaporation.
And irradiate the substrate 3 with the molecular beam to supply the material to the substrate surface.
It is a device that does.

The ratio of Bi vapor pressure to Te vapor pressure and Sb
The vapor pressure and Te vapor pressure ratios are Bi ₂ Te ₃ and Sb ₂ T, respectively.
The ratio of Te is slightly higher than the stoichiometric composition ratio of 2: 3 of e ₃ . The reason for increasing the ratio of Te is that the vapor pressure at the same temperature is much higher in Te, and Te deficiency due to re-evaporation from the generated Bi ₂ Te ₃ is prevented.

Furthermore, since the Te source for growing Bi ₂ Te ₃ and the Te source for growing Sb ₂ Te ₃ are used in common, the same Te vapor pressure is required.
Consider the vapor pressure of each of the Bi source 5 and the Sb source 6. The higher the surface temperature of the substrate, the easier the unstable molecules are re-evaporated to obtain good quality crystals, but the vapor pressure of the target product must be lower than the back pressure of the vacuum container. Therefore, from the Bi ₂ Te _3, Sb ₂ Te ₃ vapor pressure curve, when the pressure in the vacuum container 1 is set to 10 ⁻⁷ Pa, the buffer growth I, I described later is obtained.
It can be seen that in I and III, the substrate surface temperature must be set to about 270 ° C or lower.

[Method for Producing Sb ₂ Te ₃ Single Crystal Thin Film According to the Present Invention] Next, referring to FIG. 4, an Sb ₂ Te ₃ single crystal was formed on a sapphire substrate by using the MBE growth process according to the present invention, and Bi ₂ T
A method of growing an e ₃ single crystal as a buffer will be described.
In addition, in the following description, as is clear from FIG. 4 described later, the temperatures Ta1, Ta3, and Ta5 are Bi ₂ T.
The e ₃ vapor pressure is a temperature at which it becomes higher than the pressure inside the vacuum container, and the temperatures Ta2, Ta4, and T _growth are temperatures at which the Bi ₂ Te ₃ vapor pressure becomes smaller than the pressure inside the vacuum container.
First, in a high vacuum atmosphere of 10 ^-7 Pa or less (for example, 10 ^-8 Pa)
By heating the substrate 3 to the temperature Ta1 in Pa),
Evaporate and remove contaminants on the surface of the substrate 3 (Pa
1 step: thermal cleaning). Next, the temperature of the substrate surface is adjusted to Ta2 (Pa2 step:
Temperature adjustment).

Further, when the set temperature of each part reaches a thermal equilibrium state after a sufficient time has passed, the Bi shutter 11a and the Te
The shutter 11c is opened, the surface of the substrate is irradiated with the Bi molecular beam 22a and the Te molecular beam 22c to grow Bi ₂ Te ₃ on the substrate 3, and when the growth time ta3 elapses, the Bi shutter 11 is released.
Close a (Pa3 step: buffer growth I). Then, the substrate temperature is raised to Ta3, and when the temperature reaches a predetermined temperature, the heating is immediately stopped and the substrate temperature is adjusted to Ta4, whereby the Bi ₂ Te ₃ buffer layer is annealed (Pa4 step: annealing). I). And the substrate temperature is Ta
When the temperature reaches 4 and the thermal equilibrium state is reached, the Bi shutter 11 again
a is opened, and the Bi molecular beam 22a is irradiated on the substrate 3 to generate ta5.
After the growth, the Bi shutter 11a is closed (Pa5 step: buffer growth II).

Further, the substrate temperature is raised to Ta5 to anneal the Bi ₂ Te ₃ buffer layer (Pa
6th process: Annealing II). After the substrate temperature reaches Ta5, the heating is stopped immediately and the substrate 3 is grown at the crystal growth temperature T
At the same time adjusting _growth (Ta4) and so as the Bi molecular beam 22a is irradiated to the substrate 3 by opening the Bi shutter 11a, the time t _buff (ta7) until the substrate temperature decreases to T _growth (Ta4) by Bi ₂ Te ₃ single crystal buffer is grown (Pa7 process: buffer growth III).

Next, the Bi shutter 11a is closed and the Sb shutter 11b is opened to switch to Sb ₂ Te ₃ single crystal growth, and the substrate temperature is kept at T _growth (Ta4),
Sb ₂ T for the time t _growth (ta8) to obtain the desired film thickness
e ₃ perform a single crystal growth (Pa8 steps: crystal growth). After the crystal growth is completed, the Sb shutter 11b and the Te shutter 11c are closed to gradually cool the sample grown on the substrate 3 to end the growth process (Pa9 step).

[Structure of Sb ₂ Te ₃ Single Crystal Growth Sample According to the Present Invention] FIG. 5 shows the sectional structure of the Sb ₂ Te ₃ single crystal growth sample prepared by the method according to the present invention. Bi on the sapphire substrate 31 for relaxing the mismatch of lattice constants
₂ Te ₃ single crystal buffer layer 32 is provided, and this buffer layer 32
The Sb ₂ Te ₃ single crystal 33 has grown on the surface of the. At this time, the substrate temperature and each source temperature condition are the substrate temperature: 255 to 2
75 ℃, Bi source: 550 ~ 570 ℃, Te source: 310 ~ 330 ℃,
Sb source: 450-470 ° C. The preferred ranges of these temperature ranges are: substrate temperature: 255 to 265 ° C, Bi source: 558 to 562 ° C, Te source: 318 to 322 ° C, Sb source:
458-462 ° C.

[0029]

EXAMPLES Next, the present invention will be specifically described by way of examples. In this embodiment, Bi source is T _bi = 560 ° C.,
The Sb source is T _Sb = 460 ° C and the Te source is T _Te = 320 ° C.

[0030] First, the vacuum chamber 1 shown in FIG. 1 10 ^-7 P
As shown in FIG. 4, the substrate temperature is set to a high vacuum atmosphere of a.
The contaminants on the substrate surface were evaporated and removed by heating to 700 ° C. (Ta1) (Pa1 step: thermal cleaning). Next, the temperature of the substrate is adjusted to 170 ° C (Ta2), and when the set temperature of each part reaches a thermal equilibrium state after a sufficient time (Pa2 step), the substrate surface is
In order to irradiate Bi and Te source molecular beams 22a and 22c, respectively, B
Open i shutter 11a and Te shutter 11c to open Bi ₂ Te
₃ was grown, and the Bi shutter 11a was closed when the growth time of 30 seconds passed (Pa3 step: buffer growth I).

Then, the substrate temperature was raised to 345 ° C. (Ta3), and when the temperature reached a predetermined temperature, heating was stopped immediately and the substrate temperature was adjusted to 255 ° C. (Ta4) (Pa4 step: annealing I). . When the substrate temperature reaches 255 ° C (Ta4) and the thermal equilibrium state is reached, the Bi shutter 11a is opened again,
Bi shutter 11 after crystal growth for 5 minutes (ta5)
a was closed (Pb5 step: buffer growth II). Substrate temperature 40
The temperature was raised to 5 ° C. (Ta5) (Pb6 step: annealing II).
When the temperature reaches a predetermined temperature, heating is immediately stopped to adjust the substrate to a crystal growth temperature T _growth of 255 ° C., and at the same time B
The Bi ₂ Te ₃ single crystal buffer layer 32 was grown only for 20 minutes, which is the time t _buff until the substrate temperature is lowered to T _growth by opening the i shutter (Pa 7 process: buffer growth II
I).

Finally, the Bi shutter 11a is closed and the Sb shutter 11b is opened to switch to Sb ₂ Te ₃ single crystal growth, and Sb is grown for a time t _{growth at} which a desired film thickness is obtained.
₂ Te ₃ single crystal growth was performed (Pa8 process: crystal growth). After the crystal growth was completed, the Sb, Te shutter 11b11c was closed and the sample grown on the substrate 3 was gradually cooled to complete the growth process (process Pa9). The Pa4 process and the Pa6 process in the present embodiment are different in the lattice constant on the sapphire substrate 31 due to the annealing of the Bi ₂ Te ₃ single crystal buffer layer 32.
It is useful as a treatment for promoting Bi ₂ Te ₃ single crystal growth.

6 and 7 are RHEED photographs of the Sb ₂ Te ₃ single crystal film grown by the MBE growth process according to this embodiment. FIG. 6 shows the growth of the Bi ₂ Te ₃ single crystal buffer layer 32. FIG. 7 shows the state during the growth of the Sb ₂ Te ₃ single crystal. A streak pattern with vertical stripes appears in both FIGS. 6 and 7, indicating that the surface of the grown sample has become a flat single crystal at the atomic level. In addition, there is no difference in the streak interval between the two, indicating that the lattice constants are close.

Sb grown according to this example₂Te₃Single crystal thin
The X-ray diffraction result of the film sample is shown in FIG. X-ray diffraction peak
Is 41.72 °, the (0006) plane of the sapphire substrate 31, 44.66 °
To Sb ₂Te₃And buffer Bi₂Te₃Of (00015) Surface, at 54.39 °
Sb₂Te₃And Bi₂Te₃(000 of the buffer layer 3218) Other than the surface
(0009), (00012) A peak appears. Sapphire, Sb₂T
e₃Or Bi₂Te₃Only the diffraction peak corresponding to the c-plane of
On the c (0001) plane of the sapphire substrate surface
, Bi₂Te₃Buffer layer 32 and Sb₂Te₃The c-axis of layer 33 is
It can be confirmed that the single crystal has grown in the direction perpendicular to the plate surface.
It was

The present invention is not limited to the above-described embodiments, and various modifications and variations can be made based on the technical idea of the present invention. For example, as shown in FIG. 9, the Bi ₂ Te ₃ single crystal buffer layer 32 is formed on the sapphire substrate 31.
After the growth, the Sb shutter 11b and the Bi shutter 11a are alternately opened and closed to grow an alternating laminated film in which Bi ₂ Te ₃ and Sb ₂ Te ₃ are alternately laminated.

A Bi ₂ Te ₃ single crystal buffer layer 32 was formed on the sapphire substrate 31 by the same process as in FIG. 4 (Pb1
After the steps to Pb7 steps), the Te shutter 11c is opened and the Sb shutter 11b and the Bi shutter 11a are alternately opened and closed to grow a Bi ₂ Te ₃ / Sb ₂ Te ₃ alternating laminated film (Pb8 Process). Bi ₂ Te ₃ / S as many times as desired
After stacking the b ₂ Te ₃ alternating laminated films, the Sb, Bi, and Te shutters 11b, 11a, 11c are closed, and the sample grown on the substrate 3 is gradually cooled to end the growth process (Pb9 step).
FIG. 10 shows the cross-sectional structure of the Bi ₂ Te ₃ / Sb ₂ Te ₃ alternating laminated film laminated by this process. As shown in FIG. 10, a Bi ₂ Te ₃ single crystal thin film 43 and an Sb ₂ Te ₃ single crystal thin film 44 are alternately laminated on a Bi ₂ Te ₃ buffer layer 42 formed on a sapphire substrate 41. .

FIG. 11 is a graph showing the growth time and film thickness of each of the Bi ₂ Te ₃ and Sb ₂ Te ₃ layers, and the gradient of the straight line (broken line or solid line) is the growth rate of each. This graph shows the growth rate when the Bi source temperature T _Bi is 560 ° C., the Sb source temperature T _Sb is 460 ° C., and the Te source temperature T _Te is 320 ° C. as the growth temperature conditions. The growth rates of the Bi ₂ Te ₃ layer and the Sb ₂ Te ₃ layer are 106 Å / min and 105 Å / min, respectively, and by adjusting the opening times of the Bi shutter 11a and the Sb shutter 11b based on these growth rates, desired growth rates can be obtained. The film thickness can be controlled.

Bi shutter 11a and Sb shutter 1
Fig. 12 shows the X-ray diffraction analysis result of the Bi ₂ Te ₃ / Sb ₂ Te ₃ alternating laminated film sample obtained by alternately laminating the 1b for 30 seconds and 50 cycles. With this shutter open time setting, the thickness of each layer is approximately 50
It will be about Å. In FIG. 12, especially near the (000 18 ) plane peak is shown, but satellite peaks (-3, -2, -1,1,2, peculiar to the superlattice structure with the main peak (0) as the symmetry axis are shown.
3) appears and it can be confirmed that the Bi ₂ Te ₃ / Sb ₂ Te ₃ periodic structure has been formed.

[0039]

According to the present invention, a Bi ₂ Te ₃ single crystal is used as a substrate.
By using a buffer with Sb ₂ Te ₃ , a high-quality Sb ₂ T can be obtained easily and at low cost using the molecular beam epitaxy method.
An e ₃ single crystal thin film can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a molecular beam epitaxy apparatus used for manufacturing an Sb ₂ Te ₃ single crystal thin film according to the present invention.

FIG. 2 is a conceptual diagram showing a crystal structure of a trigonal system crystal.

FIG. 3 shows Bi ₂ Te ₃ used for a single crystal thin film according to the present invention,
₃ is a vapor pressure curve of Sb ₂ Te ₃ , Bi and Te.

FIG. 4 is a conceptual diagram showing a step of a growth method of an Sb ₂ Te ₃ single crystal thin film according to the present invention.

FIG. 5 is a sectional view showing the structure of an Sb ₂ Te ₃ single crystal thin film according to the present invention.

FIG. 6 shows the RH during growth of the Bi ₂ Te ₃ single crystal buffer in the case of growing the Sb ₂ Te ₃ single crystal thin film of this example.
It is an EED photograph.

FIG. 7 is a RHEED photograph during the growth of the Sb ₂ Te ₃ single crystal in the case where the Sb ₂ Te ₃ single crystal thin film of this example was grown.

FIG. 8 is a graph showing an X-ray diffraction result of a Sb ₂ Te ₃ single crystal thin film sample according to the present invention.

FIG. 9 is a conceptual diagram showing steps of a Sb ₂ Te ₃ single crystal thin film according to a modification of the present invention.

FIG. 10 is a Bi ₂ Te ₃ / Sb ₂ T according to a modification of the present invention.
It is a sectional view showing the structure of a e ₃ alternate stacked film.

FIG. 11 is a Bi ₂ Te ₃ layer and Sb according to a modification of the present invention.
Is a graph showing the respective growth time and the film thickness of ₂ Te ₃ layer.

FIG. 12 is a Bi ₂ Te ₃ / Sb ₂ T according to a modification of the present invention.
is a graph showing the X-ray diffraction pattern of e ₃ alternately laminated film sample.

[Explanation of symbols]

1 Vacuum Container 2 Exhaust Duct 3 Substrate 4 Substrate Holder 5 Bi Source 6 Sb Source 7 Te Source 8a, 8b, 8c K Cell 9a, 9b, 9c Crucible 10a, 10b, 10c Source Heater 10a, 10b, 10c Shutter 12a RHEED Electron Gun 12b RHEED screen 13 Vacuum measuring means 20 Molecular beam epitaxy apparatus 22a, 22b, 22c Molecular beam 31, 41 Sapphire substrate 32, 42 Bi ₂ Te ₃ single crystal buffer layer 33 Sb ₂ Te ₃ single crystal 42 Bi ₂ Te ₃ buffer Layer 43 Bi ₂ Te ₃ single crystal thin film 44 Sb ₂ Te ₃ single crystal thin film

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01L 35/34 H01L 35/34 (72) Inventor Takuo Uemura 317 Nishino, Numazu-shi, Shizuoka Tokai University F-term in Department of Materials Engineering, Faculty of Development Engineering (reference) 4G077 AA03 BE26 DA05 EA02 EA04 ED06 EF03 HA20 SC02 5F103 AA04 BB04 BB16 BB55 BB57 DD30 GG01 HH04 LL20 NN01 NN04 PP02 PP03 RR08

Claims (6)

[Claims] 1. Sb on a substrate placed in a closed container
_A method for producing a Sb ₂ Te ₃ single crystal thin film in which a ₂ Te ₃ epitaxial single crystal is grown, wherein Bi ₂ Te ₃ is vapor-deposited on the substrate at a substrate temperature at which the vapor pressure of Bi ₂ Te ₃ becomes smaller than the pressure in the container. a buffer growth depositing on, after raising the substrate temperature to a temperature at which Bi ₂ Te ₃ vapor pressure is greater than the pressure in the container, further, than the pressure of the Bi ₂ Te ₃ vapor pressure in the vessel The substrate was grown on the substrate by an annealing step of lowering the substrate temperature to a lower temperature and these buffer growth and annealing steps.
A method for producing an Sb ₂ Te ₃ single crystal thin film, comprising a crystal growth step of growing an Sb ₂ Te ₃ single crystal on the surface of a Bi ₂ Te ₃ epitaxial single crystal. 2. The Bi ₂ Te ₃ is deposited on the substrate by generating a Bi molecular beam and a Te molecular beam and irradiating the substrate on the substrate in the buffer growth step. A method for producing the Sb ₂ Te ₃ single crystal thin film described. 3. The Sb ₂ Te ₃ single crystal is grown by generating Sb molecular beam and Te molecular beam and irradiating the surface of the Bi ₂ Te ₃ epitaxial single crystal in the crystal growth step. The Sb ₂ Te _{3 according} to claim 1 or 2.
Method for manufacturing single crystal thin film. 4. The Bi molecular beam, the Te molecular beam and the Sb molecular beam are generated by a molecular beam epitaxy method, and the temperature condition in the molecular beam epitaxy method is that the Bi source is 5
50-570 ° C, Te source 310-330 ° C, Sb source 450-470 ° C, and substrate surface 255-27.
The method for producing an Sb ₂ Te ₃ single crystal thin film according to any one of claims 1 to 3, wherein the temperature is 5 ° C. 5. An Sb ₂ Te ₃ single crystal thin film manufactured by the method according to any one of claims 1 to 4. 6. A thermoelectric conversion element comprising the Sb ₂ Te ₃ single crystal thin film according to claim 5.