JP3841272B2 - Sb2Te3 single crystal thin film and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a Peltier element for realizing a solid state air conditioner, a thermoelectric power generation element used for recovering exhaust heat energy, a Sb ₂ Te ₃ single crystal thin film used for a thermoelectric conversion element such as a temperature sensor, and a manufacturing method thereof.
[0002]
[Prior art]
In recent years, environmental issues have become very important, and there has been a demand for energy saving by reducing the use of chlorofluorocarbons and improving heat exchange efficiency for air conditioners and coolers. A thermoelectric conversion element is promising as a reversible direct conversion element of heat energy and electric energy, but conventionally, conversion efficiency is low, so that it has not been widely spread.
As a method for improving the conversion efficiency of thermoelectric conversion elements, a quantum well structure is effective in which a very thin film with a thickness of several tens of millimeters is formed with a thermoelectric conversion material, and the film is sandwiched with a material having a wider band gap. LDHicks and others have made it clear.
[0003]
This technique is published in the literature LDHicks and MSDresselhaus, “Effect of quantum-well structures on the thermoelectric figure of merit”, Phys. Rev. B 47, 19, pp. 12727-12731 (1993).
In order to realize a quantum well structure with Bi ₂ Te ₃ which is a typical thermoelectric conversion material used in the region near room temperature, it is necessary to select a suitable barrier layer material sandwiching the quantum well layer Bi ₂ Te _3. is there. In order to stack very thin films in multiple layers, each layer must be a flat single crystal layer at the atomic level, and epitaxial single crystal growth is performed in which the upper layer crystal is grown reflecting the crystal structure of the underlying layer. 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.
[0004]
Usually, in order to grow a single crystal film on a substrate, it is necessary to select a substrate having a crystal structure and a lattice constant close to those of a target product to be grown. In the case of growing an Sb ₂ Te ₃ single crystal film, a sapphire (Al ₂ O ₃ ) substrate can be cited as a substrate having a crystal structure and a lattice constant substantially similar to Sb ₂ Te ₃ .
However, even in the lattice plane (0001) plane of this sapphire (Al ₂ O ₃ ) substrate, when trying to grow Sb ₂ Te ₃ directly on the sapphire substrate with a molecular beam epitaxy (MBE) apparatus, Sb _{Since 2} Te ₃ grows in polycrystal, it was difficult to grow a Sb ₂ Te ₃ single crystal film on a sapphire substrate.
[0005]
[Problems to be solved by the invention]
The present invention, the problems were solved by using a molecular beam epitaxy, Sb ₂ Te ₃ single crystal film Sb ₂ Te ₃ single crystal thin film and can be grown on the substrate in a simple and low cost that An object is to provide a manufacturing method.
[0006]
[Means for Solving the Problems]
Manufacturing method of Sb ₂ Te ₃ single crystal thin film according to the present invention is a sealed Sb ₂ Te ₃ method for producing a single crystal thin film to grow the Sb ₂ Te ₃ epitaxial single crystal on a substrate placed in the container in Bi ₂ Te ₃ substrate temperature be less than the pressure of the vapor pressure within the container, a buffer growth depositing a Bi ₂ Te ₃ on the substrate, than the pressure of the Bi ₂ Te ₃ vapor pressure inside the container After raising the substrate temperature to a temperature that increases, an annealing step for lowering the substrate temperature to a temperature at which the Bi ₂ Te ₃ vapor pressure becomes smaller than the pressure in the vessel, and these buffer growth steps and annealing steps A crystal growth step of growing an Sb ₂ Te ₃ single crystal on the surface of the Bi ₂ Te ₃ epitaxial single crystal grown on the substrate.
[0007]
The substrate is not particularly limited, but sapphire (Al ₂ O ₃ ) having a relatively close crystal structure and lattice constant of Sb ₂ Te ₃ single crystal 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 present invention, a high-quality Sb ₂ Te ₃ single crystal thin film can be produced by using the Bi ₂ Te ₃ single crystal thin film as a buffer layer between the substrate and the Sb ₂ Te ₃ single crystal thin film.
[0008]
Although the pressure in the said container is not specifically limited, For example, the range of 10 ^{< -6} > ^-10 <^-8> Pa is preferable. The buffer growth step and the annealing step may be performed once, but it is preferable to repeat the buffer growth step and the annealing step a plurality of times, for example, twice in order to produce a stable thin film. The processing time in the buffer growth stage is preferably 5 to 120 seconds, and more preferably 10 to 60 seconds. In addition, the processing time of an annealing stage is 1 to 10 minutes, More preferably, it is 3 to 5 minutes.
[0009]
Further, in one aspect of the method for producing a Sb ₂ Te ₃ single crystal thin film according to the present invention, in the buffer growth stage, a Bi molecular beam and a Te molecular beam are generated and irradiated onto the substrate, whereby Bi ₂ Te. _This is a method of depositing ₃ on a 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 stage, an Sb molecular beam and a Te molecular beam are generated to form a surface of the Bi ₂ Te ₃ epitaxial single crystal. In this method, Sb ₂ Te ₃ single crystals are grown by irradiation.
[0010]
Thus, as a method for depositing Bi ₂ Te ₃ on a substrate and a method for growing a Sb ₂ Te ₃ single crystal thin film on the surface of a Bi ₂ Te ₃ single crystal, general molecular beam epitaxy that does not require a special apparatus. By using this method, an Sb ₂ Te ₃ single crystal thin film can be produced at a simple and inexpensive cost.
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. In this method, the Bi source is 550 to 570 ° C, the Te source is 310 to 330 ° C, the Sb source is 450 to 470 ° C, and the substrate surface is 255 to 275 ° C.
By performing the molecular beam epitaxy method under the temperature conditions described above, a good quality Sb ₂ Te ₃ single crystal thin film can be obtained, and conversely, if it falls outside these temperature ranges, it becomes polycrystalline.
[0011]
The Sb ₂ Te ₃ single crystal thin film according to the present invention is a thin film manufactured by the method described above.
Since an Sb ₂ Te ₃ epitaxial single crystal thin film can be produced by a general molecular beam epitaxy method as a single crystal thin film growth method, it can be carried out easily and at a low cost without requiring a special apparatus.
[0012]
The thermoelectric conversion element according to the present invention is a thermoelectric conversion element using the Sb ₂ Te ₃ single crystal thin film.
This thermoelectric conversion element directly converts heat energy and electric energy reversibly and includes a Peltier element used for a solid state air conditioner, a thermoelectric power generation element used for recovering exhaust heat energy, a temperature sensor, and the like.
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 are provided. The provided thermoelectric conversion material can be obtained.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the Sb ₂ Te ₃ single crystal thin film and a manufacturing method thereof according to an embodiment of the present invention will be described in detail with reference to the drawings. In this embodiment, an example of using a molecular beam epitaxy method (hereinafter referred to as MBE method) to produce an Sb ₂ Te ₃ epitaxial single crystal thin film on a sapphire substrate via an Bi ₂ Te ₃ epitaxial single crystal thin film. Will be described.
[0014]
[Molecular beam epitaxy equipment]
The structure of a molecular beam epitaxy apparatus (hereinafter referred to as MBE apparatus) used in the present invention is schematically shown in FIG.
[0015]
The MBE apparatus 20 is shut off from the outside by the vacuum vessel 1, and the inside is held at a predetermined pressure (for example, 10 ⁻⁸ Pa) of 10 ⁻⁷ Pa or less. The vacuum vessel 1 is connected to a high vacuum exhaust means (not shown) such as a turbo molecular pump or a cryopump through an exhaust duct 2, and a 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 means and a temperature adjusting function (not shown), so that the temperature of the substrate 3 can be maintained at an arbitrary set temperature.
[0016]
Further, K cells (Knudsen Cells) 8a, 8b, 8c are arranged toward the substrate 3, and crucibles 9a, 9b, 9c, heaters 10a, 10b, 10c, and shutters that can be opened and closed are provided in the K cells. 11a, 11b, and 11c are provided. Bi (bismuth) source 5, Sb (antimony) source 6, and Te (tellurium) source 7 are filled in crucibles 9a-9c in K cells 8a-8c, and are heated by source heaters 10a-10c. It is configured to be.
[0017]
When the sources 5 to 7 are heated by the source heaters 10a to 10c, they evaporate and become molecular beams 22a, 22b, and 22c, respectively, and reach the surface of the substrate 3 without colliding with residual gas molecules in the vacuum vessel 1. It becomes a material source for thin film growth. Then, by controlling the opening and closing of the shutters 11a to 11c, elements can be selectively supplied to the surface of the substrate 3, and a desired composition material can be grown.
[0018]
Further, a reflection high energy electron diffraction (hereinafter referred to as RHEED) electron gun 12a and an RHEED screen 12b are arranged on the upper side wall of the vacuum vessel 1 so as to face the electron gun 12a. .
In the growth of the thin film, the growth surface on the substrate 3 can be observed in real time by the RHEED image. When the surface of the substrate 3 is irradiated with the electron beam 21 at an angle of 2 to 3 ° from the RHEED electron gun 12a, the reflected electron beam 21 containing the crystal structure information of the growth surface is formed on the fluorescent screen applied to the back surface of the RHEED screen 12b. Irradiated. By observing this fluorescent pattern, the crystal surface state growing on the substrate 3 can be known.
A vacuum degree measuring means 13 for measuring the degree of vacuum inside the vacuum container 1 is disposed at the upper end of the vacuum container 1. As this degree-of-vacuum measuring means 13, for example, an ionization vacuum gauge is preferably used.
[0019]
[substrate]
As described above, a single crystal close to the crystal structure of the target product to be epitaxially grown is used for the substrate 3. The target product Sb ₂ Te ₃ single crystal in the present invention belongs to a trigonal crystal as shown in FIG. 2, and has a lattice constant of a ₀ = 4.262Å and c ₀ = 30.450Å. Considering crystal growth in the c-axis direction, the substrate 3 is preferably a substrate material that is a trigonal or hexagonal crystal having the same crystal system and has a lattice constant a ₀ in the c (0001) plane. In addition, considering physical factors such as availability and surface abrasive material, the lattice constant a ₀ = 4.763A with trigonal, sapphire single crystal having a ₀ relatively close to the c ₀ = 13.003Å preferable. However, since the difference in a ₀ between Sb ₂ Te ₃ single crystal and sapphire is 11.8%, distortion occurs at the heterojunction interface between the two, which becomes an obstacle to growing a high-quality single crystal.
[0020]
Here, even if an attempt is made to grow Sb ₂ Te ₃ directly on a sapphire substrate by molecular beam epitaxy under various source temperatures and substrate temperature conditions, Sb ₂ Te ₃ becomes a polycrystal with random orientation. Therefore, an epitaxial single crystal cannot be obtained. On the other hand, the Bi ₂ Te ₃ single crystal is trigonal and has a ₀ = 4.3852Å, c ₀ = 30.483Å and a lattice constant very close to Sb ₂ Te ₃ , and a ₀ (Sb ₂ Te ₃ ). The condition of <a ₀ (Bi ₂ Te ₃ ) <a ₀ (sapphire) is satisfied. Therefore, the present invention is intended to alleviate the mismatch in the lattice constant between sapphire and Sb ₂ Te _{3 by} using Bi ₂ Te ₃ single crystal as a buffer layer between the sapphire single crystal and the Sb ₂ Te ₃ single crystal. They paid attention.
[0021]
[Vapor pressure]
FIG. 3 shows vapor pressure curves of Bi, Te, Sb as source sources and Bi ₂ Te ₃ and Sb ₂ Te ₃ as target products. The MBE apparatus heats the sources 5 to 7 against the back pressure in the vacuum vessel set to a predetermined pressure of 10 ⁻⁷ Pa or less to evaporate to generate a molecular beam. This is an apparatus for irradiating the substrate 3 and supplying a material to the substrate surface.
[0022]
Also, the ratio of Bi vapor pressure to Te vapor pressure, and the ratio of Sb vapor pressure to Te vapor pressure are slightly higher than the stoichiometric composition ratio 2: 3 of Bi ₂ Te ₃ and Sb ₂ Te ₃ respectively. To the extent. The reason why the ratio of Te is increased is that Te has a much higher vapor pressure for the same temperature, and prevents Te deficiency due to re-evaporation from the generated Bi ₂ Te ₃ .
[0023]
Further, since the Te source for Bi ₂ Te ₃ growth and the Te source for Sb ₂ Te ₃ growth are shared, the vapor pressures of the Bi source 5 and the Sb source 6 with respect to the same Te vapor pressure are considered. The higher the substrate surface temperature, the more easily unstable molecules are re-evaporated, and good quality crystals can be obtained. However, the vapor pressure of the target product must be lower than the back pressure of the vacuum vessel. Therefore, from the Bi ₂ Te _3, Sb ₂ Te ₃ vapor pressure curve, when the pressure in the vacuum vessel 1 is 10 ⁻⁷ Pa, the substrate surface temperature is about 270 ° C. or less in buffer growth I, II, III described later. It turns out that it must be set to.
[0024]
[Method for producing Sb ₂ Te ₃ single crystal thin film according to the present invention]
Next, a method for growing an Sb ₂ Te ₃ single crystal on a sapphire substrate using the Bi ₂ Te ₃ single crystal as a buffer using the MBE growth process according to the present invention will be described with reference to FIG. In the following description, as is apparent from FIG. 4 described later, the temperatures Ta1, Ta3, and Ta5 are temperatures at which the Bi ₂ Te ₃ vapor pressure becomes larger than the pressure in the vacuum vessel, and the temperatures Ta2, ta4, T _growth is the temperature at which the Bi ₂ Te ₃ vapor pressure is less than the pressure in the vacuum chamber.
First, the contaminants on the surface of the substrate 3 are evaporated and removed by heating the substrate 3 to a temperature Ta1 in a high vacuum atmosphere of 10 ⁻⁷ Pa or less (for example, 10 ⁻⁸ Pa) (Pa1 process: thermal cleaning). ).
Next, temperature adjustment is performed so that the temperature of the substrate surface becomes Ta2 (Pa2 step: temperature adjustment).
[0025]
Further, when the set temperature of each part reaches a thermal equilibrium state after a sufficient time has elapsed, the Bi shutter 11a and the Te shutter 11c are opened, and the Bi molecular beam 22a and the Te molecular beam 22c are irradiated on the substrate surface to irradiate the substrate 3. Bi ₂ Te ₃ is grown, and the Bi shutter 11a is closed when the growth time ta3 has passed (Pa3 step: buffer growth I).
The substrate temperature was then raised to Ta3, by adjusting to the substrate temperature becomes Ta4 stop quickly heated reaches the predetermined temperature, annealing of the Bi ₂ Te ₃ buffer layer (Pa4 Step: Annealing I).
When the substrate temperature reaches Ta4 and reaches a thermal equilibrium state, the Bi shutter 11a is opened again, the Bi molecular beam 22a is irradiated onto the substrate 3 to grow only ta5, and then the Bi shutter 11a is closed (Pa5 process: Buffer growth II).
[0026]
Further, the Bi ₂ Te ₃ buffer layer is annealed by raising the substrate temperature to Ta5 (Pa6 process: annealing II).
After the substrate temperature reaches Ta5, the heating is quickly stopped to adjust the substrate 3 to the crystal growth temperature T _growth (Ta4), and at the same time, the Bi shutter 11a is opened to irradiate the substrate 3 with the Bi molecular beam 22a. The Bi ₂ Te ₃ single crystal buffer is grown for the time t _buff (ta7) until the substrate temperature drops to T _growth (Ta4) (Pa7 step: buffer growth III).
[0027]
Then, close the Bi shutter 11a, by opening the Sb shutter 11b, Sb ₂ Te ₃ switch to single crystal growth, the substrate temperature while the T _growth (Ta4), the desired film thickness is obtained time t _growth ( Sb ₂ Te ₃ single crystal growth is performed only for ta8) (Pa8 step: crystal growth).
After the crystal growth is completed, the Sb shutter 11b and the Te shutter 11c are closed and the sample grown on the substrate 3 is gradually cooled to complete the growth process (Pa9 step).
[0028]
[Structure of Sb ₂ Te ₃ Single Crystal Growth Sample According to the Present Invention]
The cross-sectional structure of the Sb ₂ Te ₃ single crystal growth sample produced by the method according to the present invention is as shown in FIG. On the sapphire substrate 31, a Bi ₂ Te ₃ single crystal buffer layer 32 that relaxes mismatch of lattice constants is provided, and an Sb ₂ Te ₃ single crystal 33 is grown on the surface of the buffer layer 32. The substrate temperature and each source temperature condition at this time are substrate temperature: 255 to 275 ° C., Bi source: 550 to 570 ° C., Te source: 310 to 330 ° C., Sb source: 450 to 470 ° C. In addition, the preferable range in these temperature ranges is substrate temperature: 255-265 degreeC, Bi source: 558-562 degreeC, Te source: 318-322 degreeC, Sb source: 458-462 degreeC.
[0029]
【Example】
Next, the present invention will be described specifically by way of examples. In this embodiment, the 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 inside of the vacuum vessel 1 shown in FIG. 1 is set to a high vacuum atmosphere of 10 ⁻⁷ Pa, and the substrate temperature is heated to 700 ° C. (Ta1) as shown in FIG. (Pa1 step: thermal cleaning). Next, temperature adjustment is performed so that the substrate temperature becomes 170 ° C. (Ta2), and when sufficient time has passed and the set temperature of each part reaches the thermal equilibrium state (Pa2 process), Bi and Te source molecules are formed on the substrate surface. In order to irradiate the lines 22a and 22c, the Bi shutter 11a and the Te shutter 11c are opened to grow Bi ₂ Te ₃ and the Bi shutter 11a is closed when a growth time of 30 seconds elapses (Pa3 process: buffer growth I). .
[0031]
Next, the substrate temperature was raised to 345 ° C. (Ta 3), and when it reached a predetermined temperature, the heating was stopped immediately and the substrate temperature was adjusted to 255 ° C. (Ta 4) (Pa 4 step: annealing I). When the substrate temperature reached 255 ° C. (Ta4) and reached a thermal equilibrium state, the Bi shutter 11a was opened again, crystal growth was performed for 5 minutes (ta5), and the Bi shutter 11a was closed (Pb5 step: buffer growth II). The substrate temperature was raised to 405 ° C. (Ta5) (Pb6 process: annealing II). When the temperature reaches a predetermined temperature, heating is stopped immediately and the substrate is adjusted to the crystal growth temperature T _growth of 255 ° C., and at the same time, the time from when the Bi shutter is opened until the substrate temperature decreases to T _growth is t _buff 20 The Bi ₂ Te ₃ single crystal buffer layer 32 was grown for only one minute (Pa7 process: buffer growth III).
[0032]
Finally, closing the Bi shutter 11a, by opening the Sb shutter 11b, switching the Sb ₂ Te ₃ single crystal growth was carried out by Sb ₂ Te ₃ single crystal growth time t _growth obtained desired film thickness (Pa8 Process: Crystal growth).
After completing the crystal growth, 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 useful as a process for promoting Bi ₂ Te ₃ single crystal growth with different lattice constants on the sapphire substrate 31 by annealing the Bi ₂ Te ₃ single crystal buffer layer 32.
[0033]
6 and 7 are RHEED photographs in the case where an Sb ₂ Te ₃ single crystal film is grown by the MBE growth process according to the present embodiment. FIG. 6 shows a state in which the Bi ₂ Te ₃ single crystal buffer layer 32 is being grown. FIG. 7 shows a state during the growth of the Sb ₂ Te ₃ single crystal. Both FIG. 6 and FIG. 7 show streak patterns with vertical stripes, indicating that the surface of the growth sample has become a flat single crystal at the atomic level. Also, there is no difference in the streak interval between the two, indicating that the lattice constants are close.
[0034]
FIG. 8 shows the X-ray diffraction result of the Sb ₂ Te ₃ single crystal thin film sample grown according to this example. Peaks of X-ray diffraction, (0006) plane of the sapphire substrate 31 to 41.72 °, (000 15) surfaces of the Sb ₂ Te ₃ and the buffer Bi ₂ Te ₃ to 44.66 °, Sb ₂ Te ₃ in 54.39 ° and Bi ₂ Te ( ₃ ) In addition to the (000 18 ) plane of the buffer layer 32, (0009) and (000 12 ) peaks appear. Since only the diffraction peak corresponding to the c-plane of sapphire, Sb ₂ Te ₃ or Bi ₂ Te ₃ is observed, the Bi ₂ Te ₃ buffer layer 32 and Sb ₂ Te are formed on the c (0001) plane of the sapphire substrate surface. It was confirmed that the c-axis of the _three layers 33 was single crystal grown in a direction perpendicular to the substrate surface.
[0035]
The present invention is not limited to the above-described embodiment, and various changes or modifications can be made based on the technical idea of the present invention. For example, as shown in FIG. 9, after the Bi ₂ Te ₃ single crystal buffer layer 32 is grown on the sapphire substrate 31, the Sb shutter 11b and the Bi shutter 11a are alternately opened and closed, whereby Bi ₂ Te ₃ and Sb It is possible to grow an alternately laminated film in which ₂ Te ₃ is alternately laminated.
[0036]
After the Bi ₂ Te ₃ single crystal buffer layer 32 is formed on the sapphire substrate 31 (Pb1 step to Pb7 step) by the same process as in FIG. 4, the Sb shutter 11b and the Bi shutter 11a are opened with the Te shutter 11c open. By alternately opening and closing, a Bi ₂ Te ₃ / Sb ₂ Te ₃ alternating laminated film can be grown (Pb8 step). After the Bi ₂ Te ₃ / Sb ₂ Te ₃ alternating laminated film is laminated as many times as desired, the Sb, Bi, Te shutters 11b, 11a, 11c are closed, and the sample grown on the substrate 3 is gradually cooled to grow the process. Is finished (step Pb9).
FIG. 10 shows a 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, Bi ₂ Te ₃ single crystal thin films 43 and Sb ₂ Te ₃ single crystal thin films 44 are alternately stacked on a Bi ₂ Te ₃ buffer layer 42 formed on a sapphire substrate 41. .
[0037]
FIG. 11 is a graph showing the growth time and film thickness of each layer of Bi ₂ Te ₃ and Sb ₂ Te ₃ , and the gradients of straight lines (broken lines or solid lines) represent the growth rates. This graph shows the growth rate when the Bi source temperature T _{Bi is set} to 560 ° C., the Sb source temperature T _{Sb is set} to 460 ° C., and the Te source temperature T _{Te is set} to 320 ° C. as 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. By adjusting the opening times of the Bi shutter 11a and the Sb shutter 11b based on these growth rates, desired growth rates are obtained. The film thickness can be controlled.
[0038]
The open time of the Bi shutter 11a and the Sb shutter 11b is 30 seconds each, and 50 cycles are alternately laminated, and the X-ray diffraction analysis result of the Bi ₂ Te ₃ / Sb ₂ Te ₃ alternating laminated film sample obtained by this is shown in FIG. 12 shows.
With this shutter opening time setting, the thickness of each layer is expected to be about 50 mm. FIG. 12 particularly shows the vicinity of the (000 18 ) plane peak, but the satellite peak (-3, -2, -1,1,2,3) peculiar to the superlattice structure with the main peak (0) as the axis of symmetry. ) Appears, and it can be confirmed that a periodic structure of Bi ₂ Te ₃ / Sb ₂ Te ₃ can be formed.
[0039]
【The invention's effect】
According to the present invention, by using a Bi ₂ Te ₃ single crystal as a buffer between a substrate and Sb ₂ Te ₃ , a high-quality Sb ₂ Te ₃ single crystal can be obtained at a simple and inexpensive cost using a molecular beam epitaxy method. A thin film can be obtained.
[Brief description of the 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 crystal.
FIG. 3 is a vapor pressure curve of Bi ₂ Te ₃ , Sb ₂ Te ₃ , Bi and Te used for the single crystal thin film according to the present invention.
FIG. 4 is a conceptual diagram showing the steps of the growth method of the Sb ₂ Te ₃ single crystal thin film according to the present invention.
FIG. 5 is a cross-sectional view showing the structure of a Sb ₂ Te ₃ single crystal thin film according to the present invention.
FIG. 6 is a RHEED photograph during growth of a Bi ₂ Te ₃ single crystal buffer when an Sb ₂ Te ₃ single crystal thin film of this example is grown.
FIG. 7 is an RHEED photograph during the growth of Sb ₂ Te ₃ single crystal when the Sb ₂ Te ₃ single crystal thin film of this example is 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 a process of an Sb ₂ Te ₃ single crystal thin film according to a modification of the present invention.
FIG. 10 is a cross-sectional view showing the structure of a Bi ₂ Te ₃ / Sb ₂ Te ₃ alternating laminated film according to a modification of the present invention.
FIG. 11 is a graph showing the growth time and film thickness of each of a Bi ₂ Te ₃ layer and an Sb ₂ Te ₃ layer according to a modification of the present invention.
12 is a graph showing an X-ray diffraction result of a Bi ₂ Te ₃ / Sb ₂ Te ₃ alternating film sample according to a modification of the present invention. FIG.
[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 cells 9a, 9b, 9c Crucibles 10a, 10b, 10c Source heaters 10a, 10b, 10c Shutter 12a RHEED electrons 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

Claims (6)

A sealed Sb ₂ Te ₃ method for producing a single crystal thin film to grow the Sb ₂ Te ₃ epitaxial single crystal on a substrate placed in the container,
In Bi ₂ Te ₃ substrate temperature be less than the pressure of the vapor pressure within the container, a buffer growth depositing a Bi ₂ Te ₃ on the substrate, greater than the pressure of the Bi ₂ Te ₃ vapor pressure in the vessel After the substrate temperature is raised to a temperature, the annealing step of lowering the substrate temperature to a temperature at which the Bi ₂ Te ₃ vapor pressure becomes smaller than the pressure in the vessel, and the buffer growth step and the annealing step, A method for producing a Sb ₂ Te ₃ single crystal thin film comprising a crystal growth step of growing Sb ₂ Te ₃ single crystal on a surface of a Bi ₂ Te ₃ epitaxial single crystal grown on a substrate. _2. The Sb ₂ Te according to claim 1, wherein in the buffer growth stage, 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. ₃ Manufacturing method of single crystal thin film The Sb ₂ Te ₃ single crystal is grown by generating an Sb molecular beam and a Te molecular beam and irradiating the surface of the Bi ₂ Te ₃ epitaxial single crystal in the crystal growth step. or Sb ₂ Te ₃ method for producing a single crystal thin film according to 2. The Bi molecular beam, Te molecular beam and Sb molecular beam are generated by molecular beam epitaxy, and the temperature conditions in the molecular beam epitaxy are as follows: Bi source is 550 to 570 ° C., Te source is 310 to 330 ° C., Sb The method for producing a Sb ₂ Te ₃ single crystal thin film according to any one of claims 1 to 3, wherein the source is 450 to 470 ° C and the substrate surface is 255 to 275 ° C. Sb ₂ Te ₃ single crystal thin film characterized by being manufactured by the method claimed in any one of the claims 1-4. A thermoelectric conversion element using the Sb ₂ Te ₃ single crystal thin film according to claim 5.

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