Bi2Te3 Sb2Te3 Research Articles

A High Power Density Micro-Thermoelectric Generator Fabricated by an Integrated Bottom-Up Approach

In this paper, we report a high power density cross-plane micro-thermoelectric generator (TEG) fabricated by integrating pulsed electroplating with micro-fabrication processes. The TEG consists of a total of 127 pairs of n-type Bi2Te3 and p-type Sb2Te3 thermoelectric pillars embedded in a SU-8 matrix in order to enhance the overall mechanical strength of the device. Both bottom and top electrical connections are formed by electroplating, which is advantageous because of facile and low cost fabrication and low parasitic electrical resistances. The device demonstrates a maximum power of 2990 $\mu \text{W}$ at a temperature difference of 52.5 K, corresponding to a power density as high as 9.2 mW $\cdot $ cm $^{-2}$ . The power density of our device is more than two times the highest value reported for the electroplated micro-TEGs in the literature, which can be attributed to the low internal resistance and high packing density of thermoelectric pillars. [2015-0348]

Separation of Contributions from the Ion Core and Free Charge Carriers to the Magnetic Susceptibility of an Anisotropic Semiconductor Bi2Te3–Sb2Te3 Crystal

A technique is presented, by which the magnetic susceptibility χ | of the ion core of an anisotropic semiconductor Bi2Te3–Sb2Te3 crystal is determined from experimental data on the magnetic susceptibility χ ∥ and χ ⊥ obtained with allowance for the orientation of the magnetic field vector H with respect to the trigonal C3 axis of the crystal in accordance with the expression χ ∥/χ ⊥ = (χ ∥ + χ G )/(χ ⊥ + χ G ).In this expression, the value of the magnetic susceptibility of free charge carriers χ ∥ and χ ⊥ depending on their effective masses m ∥ * and m ⊥ * known from the experiment is calculated within the framework of the Pauli and Landau- Peierls approaches. The found value of χ | for Bi2Te3–Sb2Te3 crystals is in good agreement with experimental data, as well as with the estimates obtained in the framework of the Larmor approach explaining, in particular, a linear dependence of the molar magnetic susceptibility on the number of electrons in the molecule observed for a large number of compounds. The proposed technique can be extended to other anisotropic semiconductors.

Micro-Power Generation Characteristics of Thermoelectric Thin Film Devices Processed by Electrodeposition and Flip-Chip Bonding

A thermoelectric thin film device of cross-plane configuration was fabricated by the flip-chip process using an anisotropic conductive adhesive. The Cu/Au bonding bumps electrodeposited on the Ti/Cu/Au electrodes in the top substrate were flip-chip bonded to the 242 pairs of the n-type Bi2Te3 and p-type Sb2Te3 thin film legs electrodeposited on the Ti/Cu/Au electrodes in the bottom substrate. Using the output voltage–current curve, the internal resistance of the thin film device was measured to be 21.4 Ω at temperature differences of 9.8–39.7 K across the device. The thin film device exhibited an open-circuit voltage of 320 mV and a maximum output power of 1.1 mW with a power density of 3.84 mW/cm2 at a temperature difference of 39.7 K applied across the thin film device.

English

The principal motivation of this work is the development and realization of anemometers based butterfly structureelaborated by flash evaporation technique on polyimide substrate using Bi2Te3–Sb2Te3(P) and Bi2Te3– Bi2Se3(N) materials which best values of Seebeck coefficient (􀟙(T)) at room temperature are found to be 240 􀟤V/K and -220 􀟤V/K, respectively. These anemometers are based on both Peltier and Joule effects. We elaborate a particular geometry in order to improve the sensitivity of butterfly structuresensors. Fabrication and evaluation of performance devices are reported 2.3°C of cooling of only one Peltier module device for an optimal current of Iopt = 18mA is obtained.

Facile hydrothermal synthesis and formation mechanisms of Bi2Te3, Sb2Te3 and Bi2Te3–Sb2Te3 nanowires

A facile and “green” glucose-assisted hydrothermal method is proposed to synthesize Bi2Te3, Sb2Te3 and Bi2Te3–Sb2Te3 nanowires.

Preparation and Characterization of Bi2Te3/Sb2Te3 Thermoelectric Thin-Film Devices for Power Generation

A device based on a new double-layer-leg thin-film concept has been successfully fabricated by flip-chip bonding of 242 pairs of n-type Bi2Te3 and p-type Sb2Te3 thin-film legs electrodeposited on top substrates to those processed on bottom substrates. Based on the output voltage–current curve, the internal resistance of the double-layer-leg thin-film device was measured to be 3.47 kΩ at an apparent temperature difference of 25.9 K across the device. The actual temperature difference across the thin-film legs was estimated to be 3.51 K, which is ∼13% of the apparent temperature difference ΔT of 25.9 K applied across the thin-film device. The double-layer-leg thin-film device exhibited an open-circuit voltage of 0.43 V and maximum output power of 13.1 μW at an apparent temperature difference ΔT of 25.9 K.

Thermoelectric Power Generation Characteristics of a Thin-Film Device Consisting of Electrodeposited n-Bi2Te3 and p-Sb2Te3 Thin-Film Legs

A thermoelectric thin-film device of the cross-plane configuration was fabricated by flip-chip bonding of the top electrodes to 242 pairs of electrodeposited n-type Bi2Te3 and p-type Sb2Te3 thin-film legs on the bottom substrate. The electrodeposited Bi2Te3 and Sb2Te3 films of 20-μm thickness exhibited Seebeck coefficients of −59 μV/K and 485 μV/K, respectively. The internal resistance of the thin-film device was measured as 3.7 kΩ, most of which was attributed to the interfacial resistance of the flip-chip joints. The actual temperature difference ΔTG working across the thin-film legs was estimated to be 10.4 times smaller than the apparent temperature difference ΔT applied across the thin-film device. The thin-film device exhibited an open-circuit voltage of 0.294 V and a maximum output power of 5.9 μW at an apparent temperature difference ΔT of 22.3 K applied across the thin-film device.

Thermoelectric Characteristics of n-Type Bi<sub>2</sub>Te<sub>3</sub> and p-Type Sb<sub>2</sub>Te<sub>3</sub> Thin Films Prepared by Co-Evaporation and Annealing for Thermopile Sensor Applications

A thermoelectric thin-film device consisting of n-type Bi2Te3 and p-type Sb2Te3 thin-film legs was prepared on a glass substrate by using co-evaporation and annealing process. The Seebeck coefficient and the power factor of the co-evaporated Bi2Te3 film were −30 µV/K and 0.7 × 10−4 W/K2·m, respectively, and became substantially improved to −160 µV/K and 16 × 10−4 W/K2·m by annealing at 400°C for 20 min. While the Seebeck coefficient of the co-evaporated Sb2Te3 thin film was 72 µV/K, it increased significantly to 165–142 µV/K by annealing at 200–400°C for 20 min. A maximum power factor of 25 × 10−4 W/K2·m was achieved for the co-evaporated Sb2Te3 film by annealing at 400°C for 20 min. A thermopile sensor consisting of 10 pairs of n-type Bi2Te3 and p-type Sb2Te3 thin-film legs exhibited a sensitivity of 2.7 mV/K.

Bi-Sb-Te Based Thin Film Thermoelectric Generator

N-type Bi2Te3 and p-type Sb2Te3 thermoelectric thin films have been prepared by RF and DC co-sputtering. The Seebeck coefficient of n-type Bi2Te3 and p-type Sb2Te3 thin films is about -122 μVK-1 and 108 μVK-1, the power factor is about 0.82×10-3 Wm-1K-2 and 1.60×10-3 Wm-1K-2. Then, the films have been selected to fabricate the thin film thermoelectric generator. The results show that the open-circuit voltage of 12.2 mV and the output power of 3.32 μW are obtained for a thin film generator with the temperature difference at 60 K.

High pressure transport characteristics of Bi2Te3, Sb2Te3, and BiSbTe3

This paper presents ambient and high pressure measurements of transport properties of the Bi2Te3–Sb2Te3 series of materials. The electrical resistivity, thermal conductivity, and Seebeck coefficient have been measured on both end compounds and the direct solid solution of the two at pressure up to 10GPa. An additional discussion involving the high pressure structure will be presented. From this, it was determined that these materials undergo at least two structural phase transitions between 0 and 20GPa and a discussion is presented regarding this and the changes in the transport properties.

Influence of nanoinclusions on scattering of holes and phonons and transport coefficients in BixSb1−xTe3 bulk nanostructures

One of the possible ways to increase the thermoelectric figure of merit is the use of bulk nanostructured materials fabricated by melt spinning with subsequent hot pressing or spark plasma sintering. Among a variety of nanostructure types these materials contain regions of initial solid solution with nanometer sized inclusions of different compositions. In the present work the scattering of holes and phonons on nanoinclusions in such p-BixSb1−xTe3 based materials is considered. The change of transport coefficients due to this scattering mechanism is theoretically estimated. The estimations showed that the reduction of lattice thermal conductivity (about 12–13%) for nanoinclusions of Bi2Te3–Sb2Te3 solid solution with different compositions is much greater than the change in power factor. Therefore the corresponding increase of the thermoelectric figure of merit for this case is determined mainly by phonon scattering. Also it is shown that the results of estimations depend on phonon spectrum approximation, e.g. in the case of sine-shaped instead of linear phonon spectrum the estimations give two times higher thermal conductivity reduction.

Dispenser printed composite thermoelectric thick films for thermoelectric generator applications

This paper describes novel processes for preparing thermoelectric composite materials compatible with thick film dispenser printing fabrication processes. Optimization of process parameters to improve thermoelectric properties is introduced. We explore the use of n-type Bi2Te3 and p-type Sb2Te3 materials to achieve properties suitable for use in low cost high aspect ratio microscale thermoelectric generators. Printable thermoelectric inks consisted of dispersed semiconductor powders in an epoxy resin system. Thick films were printed on glass substrates and cured at temperatures ranging from 150 to 350 °C. The best achievable power factors for n-type Bi2Te3-epoxy and p-type Sb2Te3-epoxy composite films were 1.5×10−4 W/m K2 and 8.4×10−4 W/m K2, respectively. Figure of merit (ZT) values for n-type Bi2Te3-epoxy and p-type Sb2Te3-epoxy composites were 0.16 and 0.41, respectively, which are much higher than previously reported ZT values for composite thermoelectric materials.

Sb2Te3 and Bi2Te3 Thin Films Grown by Molecular Beam Epitaxy at Room Temperature

ABSTRACTNano-alloyed p-type Sb2Te3 and n-type Bi2Te3 thin films were grown on SiO2/Si and BaF2 substrates by molecular beam epitaxy (MBE) in two steps: (i) Repeated deposition of five-layer stacks with sequence Te-X-Te-X-Te (X = Sb or Bi) with elemental layer thicknesses of 0.2 nm on substrates at room temperature, (ii) annealing at 250 °C for two hours at which phase formation of Sb2Te3 or Bi2Te3 occurred. The room temperature MBE deposition method reduces surface roughness, allows the use of non lattice-matched substrates, and yields a more accurate and easier control of the Te content compared to Bi2Te3 thin films, which were epitaxially grown on BaF2 substrates at 290 °C. X-ray diffraction revealed that the thin films were single phase, poly-crystalline, and textured. The films showed grain sizes of 500 nm for Sb2Te3 and 250 nm for Bi2Te3, analyzed by transmission electron microscopy (TEM). The in-plane transport properties (thermopower S, electrical conductivity σ, charge carrier density n, charge carrier mobility μ, power factor S2σ) were measured at room temperature. The nano-alloyed Sb2Te3 thin film revealed a remarkably high power factor of 29 μW cm-1 K-2 similar to epitaxially grown Bi2Te3 thin films and Sb2Te3 single crystalline bulk materials. This large power factor can be attributed to a high charge carrier mobility of 402 cm2 V−1 s-1 similar to high-ZT Bi2Te3/Sb2Te3 superlattices. However, for the nano-alloyed Bi2Te3 thin film a low power factor of 8 μW cm−1 K-2 and a low charge carrier mobility of 80 cm2 V−1 s−1 were found. Detailed microstructure and phase analyses were carried out by energy-filtered TEM in cross-sections. Quantitative chemical analysis by energy-dispersive x−ray spectroscopy (EDS) was also applied. In Bi2Te3 thin films, few nanometer thick Bi-rich blocking layers at grain boundaries and Te fluctuations by 1.3 at.% within the grains were observed. The small charge carrier densities are explained by a reduced antisite defect density due to the low temperatures to which the thin films were exposed during annealing.

Fabrication and characterization of Bi-Sb-Te based thin film thermoelectric generator prepared by ion beam sputtering deposition

In this paper, N-type Bi2Te3 and p-type Sb2Te3 thermoelectric thin films are deposited by ion beam sputtering with Bi/Te and Sb/Te binary compound target. Sb2Te3 thin films and Bi2Te3 thin films are annealed at different annealing temperatures for 1 h and their thermoelectric properties are characterized. When the annealing temperature is 150 ℃, both the Seebeck coefficient and power factor of the Bi2Te3 thin films have maximal values of -148 μVK-1 and 0.893×10-3 Wm-1K-2 respectively. Sb2Te3 thermoelectric thin film has a seebeck coefficient of 117 μVK-1 and a maximal power factor of 0.797×10-3 Wm-1K-2 when the annealing temperature is 200 ℃. Therefore, Sb2Te3 thin films at the annealing temperature of 200 oC and Bi2Te3 thin films at the annealing temperature of 150 ℃ are selected to fabricate the single thin film thermoelectric generation. When the temperature difference between the cold side and the heat side is 50K, the output voltage of the single thin film thermoelectric generation is 15.26 mV and the maximal output power is 0.129 μW.

Thermoelectric Properties of Bi<sub>2</sub>Te<sub>3</sub>/Sb<sub>2</sub>Te<sub>3</sub> Thin Films

The deposition and characterization of n-type Bi2Te3 and p-type Sb2Te3 semiconductor films are reported. The films were deposited by thermal co-evaporation on a 25 µm thick polyimide (kapton) substrate. The co-evaporation method is inexpensive, simple, and reliable, when compared to other techniques that need longer time periods to prepare the starting material or require more complicated and expensive deposition equipment. Seebeck coefficients of -189 µVK-1 and +140 µVK-1 and electrical resistivities of 7.7 µ0m and 15.1 µ0m were measured at room temperature on n-type and p-type films, respectively. These values are better than those reported for films deposited by co-sputtering or electrochemical deposition, and are close to those reported for films deposited by metal-organic chemical vapour deposition or flash evaporation. Because of their high figures of merit, these films will be used for the fabrication of a micro-Peltier element, useful in temperature control and laser-cooling for telecommunications.

In-situ monitoring of the growth of Bi2 Te2 and Sb2 Te3 films and Bi2 Te3-Sb2 Te3 superlattice using spectroscopic ellipsometry

In this work, we present in-situ monitoring of the growth of bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) thin films as well as Bi2 Te3-Sb2Te3 superlattice using a spectroscopic ellipsometer (SE). Bi2Te3 and Sb2 Te3 films were grown by metalorganic chemical vapor deposition (MOCVD) at 350 C. A44-wavelength ellipsometer with spectral range from 404 nm to 740 nm was used in this work. The optical constants of Bi2 Te3 and Sb2Te3 at growth temperature were determined by fitting a model to the extracted in-situ SE data of optically thick Bi2 Te3 and Sb2 Te3 films. Compared to the optical constants of Bi2 Te3 and Sb2 Te3 at room temperature, significant temperature dependence was observed. Using their optical constants at growth temperature, the in-situ growth of Bi2 Te3 and Sb2 Te3 thin films were modeled and excellent fit between the experimental data and data generated from the best-fit model was obtained. In-situ growth of different Bi2 Te3-Sb2 Te3 superlattices was also monitored and modeled. The growth of Bi2 Te3 and Sb2 Te3 layers can be seen clearly in in-situ SE data. Modeling of in-situ superlattice growth shows perfect superlattice growth with an abrupt interface between the two constituent films.

Improving yield and performance in pseudo-ternary thermoelectric alloys (Bi2Te3)(Sb2Te3)(Sb2Se3)

Abstract Thermoelectric alloys of Bi 2 Te 3 Sb 2 Te 3 Sb 2 Se 3 have typically been fabricated by Bridgman growth and zone growth [1, 2]. This study showed that the method of growth does not appear to produce a significant difference in the figure of merit. However, it was found that the zone techniques can produce a higher yield of material than Bridgman techniques in both the p- and n-type material without a degradation in the high figure of merit. The maximum figure of merit for p-type alloy (Bi 2 Te 3 ) 72 (Sb 2 Te 3 ) 25 (Sb 2 Se 3 ) 3 was found to be 3.6 × 10 −3 K −1 and for the n-type (Bi 2 Te 3 ) 90 (Sb 2 Te 3 ) 5 (Sb 2 Se 3 ) 5 , 3.2 × 10 −3 K −1 [1].

Thermoelectric properties of p-type Bi2Te3–Sb2Te3–Sb2Se3 alloys and n-type Bi2Te3–Bi2Se3 alloys in the temperature range 300 to 600 K

A conventional absolute method was used for the measurement of the thermal conductivity of pressed and sintered p-type Bi2Te3–Sb2Te3–Sb2Se3 alloys and n-type Bi2Te3–Bi2Se3 alloys in the temperature range of 300 to 600 K. The measurements were made in directions parallel and perpendicular to the pressing direction. Measurements of the Seebeck coefficient and the electrical resistivity for these alloys were performed between 300 and 575 K in the pressing direction only. The maximum values of the figure of merit for the p- and n-type samples are 17 × 10−1 and 16 × 10−4 K−1, respectively. It is concluded that a thermoelectric generator, having these alloys for its p- and n-branches will attain its highest efficiency in the temperature range between 370 and 480 K. Die thermoelektrischen Eigenschaften von gepresten und gesinterten p-leitenden Bi2Te3–Sb2Te3–Sb2Se3 und n-leitenden Bi2Te3–Bi2Se3 Legierungen wurden im Temperaturbereich 300 bis 600 K mit einer konventionellen Methode untersucht. Diese Messungen wurden parallel und senkrecht zur Presrichtung durchgefuhrt. Der Seebeckkoeffizient und der elektrische Widerstand dieser Legierungen wurden im Temperaturbereich 300 bis 575 K nur in Presrichtung gemessen. Die Maximalwerte der Leistungsfaktoren von p- und n-leitenden Proben betragen 17 × 10−4 bzw. 16 × 10−4 K−1. Daraus folgt, das ein thermoelektrischer Generator mit diesen Legierungen als p- bzw. n-Zweig seine hochste Leistungsfahigkeit im Temperaturbereich 370 bis 480 K erreicht.

Thermoelectric Cooling Elements in Powder Metallurgy

The thermoelectric properties of Bi-Te binary and Bi2Te3-Sb 2Te3, Bi2Te3-Bi2Se3 ternary alloys with some additional elements, prepared by powder metallurgy has been studied. The effects of particle size, compacting pressure, sintering condition, and an anisotropy of the thermoelectric elements was experimented. The results show that the specimens prepared by powder metallurgy has the figure of merit Z values almost equal to those of specimen of same composition prepared by melting method. The sintered thermoelement has higher ρ value than the melted element, and is therefore suitable for the objects used by low optimum current.

Properties of Bi2Te3-Sb2Te3 Alloys

The phase diagram for the Bi2Te3–Sb2Te3 pseudo-binary system is of the solid-solution type, where the distribution coefficient k is equal to unity at 33.3 and 66.7 mole % Sb2Te3. The c lat tice parameter remains essentially constant across the diagram at 30.49 Å for both slowly crystallized and quenched alloys. For quenched alloys the a lattice parameter decreases almost linearly, from a value of 4.487 Å, for pure Bi2Te3, to a value of 4.275 Å, for pure Sb2Te3; however, a significant contraction from linear variation is found in slowly crystallized materials. EG diminishes in an essentially linear fashion from 0.16 eV, for pure Bi2Te3, to 0.12 eV at 24.2 mole % Sb2Te3 in both slowly crystallized and quenched materials. EG remains approximately constant from 24.2 to 66.7 mole % Sb2Te3 for slowly crystallized materials but continues to drop for quenched materials.