Electrophysical properties and electronic structure of tin-doped antimony telluride

The effect of Sn atoms on the electrophysical properties and x-ray photoelectron spectra of Czochralski-grown Sb₂Te₃ single crystals is studied. The character of the temperature dependences of the kinetic coefficients is shown to depend noticeably on the structure of the valence band, which consists of two valence subbands. Estimates of the effective density-of-states masses of holes and of the gap between the valence-band extrema in Sb₂Te₃: Sn agree with the data available for the Sb₂Te₃ not doped with tin. X-ray photoelectron spectra of Sb₂Te₃: Sn single crystals do not exhibit noticeable core-level shifts and electron density redistribution in the valence band.     

Sb2Te3 纳米结构的制备与表征

以室温热电性能优异的传统热电材料Sb₂Te₃为研究对象,利用化学气相沉积法制备Sb₂Te₃单晶纳米结构,并研究其生长机理.实验结果表明,不加催化剂时Sb₂Te₃易生长成六方纳米盘,在金催化剂条件下定向生长成纳米线.Sb₂Te₃的形貌与其晶体结构和生长机理有关.Sb₂Te₃为三角结构,Sb和     

Microstructures and thermoelectric properties of GeSbTe based layered compounds

Microstructures and thermoelectric properties of Ge₁Sb₂Te₄ and Ge₂Sb₂Te₅ chalcogenide semiconductors have been investigated to explore the possibility of their thermoelectric applications. The phase transformation from the face-centered cubic to hexagonal structure was observed in Ge₂Sb₂Te₅ compounds prepared by the melt spinning technique. The Seebeck coefficient and electrical resistivity of the alloys were increased due to the enhanced scattering of charge carriers at grain boundaries. The maximum power factors of the rapidly solidified Ge₁Sb₂Te₄ and Ge₂Sb₂Te₅ attained 0.975×10^-3 W m^-1K^-2 at 750 K and 0.767×10^-3 W m^-1K^-2 at 643 K respectively, higher than those of water quenched counterparts, implying that thermoelectric properties of GeSbTe based layered compounds can be improved by grain refinement. The present results show this class of chalcogenide semiconductors is promising for thermoelectric applications. PACS  84.60.Rb; 81.05.Hd; 72.20.Pa; 64.70.Kb; 61.66.Fn     

Effective Mass Enhancement and Thermal Conductivity Reduction for Improving the Thermoelectric Properties of Pseudo-Binary Ge2Sb2Te5

Ge₂Sb₂Te₅ is a famous phase-change memory material for rewriteable optical storage, which is widely applied in the information storage field. The stable trigonal phase of Ge₂Sb₂Te₅ shows potential as a thermoelectric material as well, due to its tunable electrical transport properties and low lattice thermal conductivity. In this work, the carrier concentration and effective mass of Ge₂Sb₂Te₅ are modulated by substituting Te with Se. Meanwhile, the thermal conductivity reduces from 2.48 W m⁻¹ K⁻¹ for Ge₂Sb₂Te₅ to 1.37 W m⁻¹ K⁻¹ for Ge₂Sb₂Te_3.5Se_1.5 at 703 K. Therefore, the thermoelectric figure of merit zT increases from 0.24 for Ge₂Sb₂Te₅ to 0.41 for Ge₂Sb₂Te_3.5Se_1.5 at 703 K. This study reveals that Se alloying is an effective way to enhance the thermoelectric properties of Ge₂Sb₂Te₅.     

Thermal sensors based on Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript> and (Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>)<Subscript>70</Subscript>(Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>)<Subscript>30</Subscript> thin films

Thin films of Sb₂Te₃ and (Sb₂Te₃)₇₀(Bi₂Te₃)₃₀ alloy and have been deposited on precleaned glass substrate by thermal evaporation technique in a vacuum of 2?×?10^?6 Torr. The structural study was carried out by X-ray diffractometer, which shows that the films are polycrystalline in nature. The grain size, microstrain and dislocation density were determined. The Seebeck coefficient was determined as the ratio of the potential difference across the films to the temperature difference. The power factor for the (Sb₂Te₃)₇₀ (Bi₂Te₃)₃₀ and (Sb₂Te₃) is found to be 19.602 and 1.066 of the film of thickness 1,500 Å, respectively. The Van der-Pauw technique was used to measure the Hall coefficient at room temperature. The carrier concentration was calculated and the results were discussed.     

Improving the thermoelectric properties of thick Sb2Te3 film via Cu doping and annealing deposited by DC magnetron sputtering using a mosaic target

Thick Cu-doped Sb₂Te₃ films were deposited on flexible substrate by DC magnetron sputtering from a mosaic Cu–Sb₂Te₃ target. The Cu-doped Sb₂Te₃ films were vacuum annealed to improve their thermoelectric properties. Density functional theory was used to clarify the internal mechanism of the Cu doped into the Sb₂Te₃ system. The results showed that Cu substitution on a Sb site induced electronic states or impurity peaks of Sb₂Te₃ at a valence band maximum. The carrier concentration of the Cu-doped Sb₂Te₃ films increased as the Cu-doped concentration increased. However, the crystallite size and Seebeck coefficient of the Cu-doped Sb₂Te₃ films decreased as the Cu-doped concentration increased. Post-annealing treatment improved the microstructure and thermoelectric properties of the Cu-doped Sb₂Te₃ films. The maximum electrical conductivity and power factor values of 754.20 S/cm at 50 °C and 1.56 10⁻³ W/mK² at 100 °C were obtained in the annealed film with a Cu-doped concentration of 3 at%.     

Bi-Sb-Te基热电薄膜温差电池离子束溅射制备与表征

本文采用离子束溅射Bi/Te和Sb/Te二元复合靶,直接制备n型Bi₂Te₃热电薄膜和p型Sb₂Te₃热电薄膜.在退火时间同为1 h的条件下,对所制备的Bi₂Te₃薄膜和Sb₂Te₃薄膜进行不同温度的退火处理,并对其热电性能进行表征.结果表明,在退火温度为150 ℃时,制备的n型Bi₂Te₃关键词： 薄膜温差电池 2Te₃薄膜')" href="#">Sb₂Te₃薄膜 2Te₃薄膜')" href="#">Bi₂Te₃薄膜 离子束溅射     

Evaluation of Thermoelectric Properties of Ag0.366Sb0.558Te

Ternary AgSbTe₂ materials are frequently reported to show a promising thermoelectric performance, due to the intrinsically low lattice thermal conductivity and complex valence band structure. However, stoichiometric AgSbTe₂ is found to be thermodynamically unstable and would partially decompose into Ag₂Te and Sb₂Te₃ during thermal cycling. Instead, Ag_0.366Sb_0.558Te is the composition for stabilizing the single-phase according to the Ag₂Te-Sb₂Te₃ phase diagram, while the thermoelectric transport properties have rarely been reported and are the focus of this work. Sn/Sb substitution is found to effectively increase not only the carrier concentration from ≈5 × 10¹⁹ cm⁻³ to ≈4 × 10²¹ cm⁻³, but also the density-of-states effective mass, leading to an enhanced Seebeck coefficient along with a decreased carrier mobility. Single parabolic band (SPB) model with acoustic phonon scattering enables a good understanding on the charge transport. The increased carrier concentration effectively suppresses the bipolar effect at high temperatures. As a result, a peak zT of ≈1.3 and an average of ≈0.9 are achieved.     

On the metal distribution in the system GeTe−Sb2Te3

The structures of GeSb₂Te₄, Ge₂Sb₂Te₅ and GeSb₄Te₇ are not determined completely by means of classical X-ray or electron diffraction studies. We have measured the Mössbauer parameters of¹²¹Sb in these compounds as well as in their binary constituent Sb₂Te₃ as an attempt to improve our knowledge on the question.     

Ge/Sb2Te3 nanocomposite multilayer films for high data retention phase-change random access memory application

The amorphous-to-crystalline transition of Ge/Sb₂Te₃ nanocomposite multilayer films with various thickness ratios of Ge to Sb₂Te₃ were investigated by utilizing in situ temperature-dependent film resistance measurements. The crystallization temperature and activation energy for the crystallization of the multilayer films increased with the increase in thickness ratio of Ge to Sb₂Te₃. The difference in sheet resistance between amorphous and crystalline states could reach as high as 10⁴ Ω/□. The crystallization temperature and activation energy for the crystallization of Ge/Sb₂Te₃ nanocomposite multilayer films was proved to be larger than that of conventional Ge₂Sb₂Te₅ film, which ensures a better data retention for phase-change random access memory (PCRAM) use. A data retention temperature for 10 years of the amorphous state [Ge (2 nm)/Sb₂Te₃ (3 nm)]₄₀ film was estimated to be 165 °C. Transmission electron microscopy (TEM) images revealed that Ge/Sb₂Te₃ nanocomposite multilayer films had layered structures with clear interfaces.     

基于Si掺杂Sb2Te3薄膜的相变存储器研究

采用磁控三靶(Si，Sb及Te)共溅射法制备了Si掺杂Sb₂Te₃薄膜，作为对比，制备了Ge₂Sb₂Te₅和Sb₂Te₃薄膜，并且采用微加工工艺制备了单元尺寸为10μm×10μm的存储器件原型来研究器件性能.研究表明，Si掺杂提高了Sb₂Te₃薄膜的晶化温度以及薄膜的晶态和非晶态电阻率，使得其非晶态与晶态电阻率之比达到10⁶，提高了器件的电阻开/关比；同Ge₂Sb₂Te₅薄膜相比，16at% Si掺杂Sb₂Te₃薄膜具有较低的熔点和更高的晶态电阻率，这有利于降低器件的RESET电流.研究还表明，采用16at% Si掺杂Sb₂Te₃薄膜作为存储介质的存储器器件原型具有记忆开关特性，可以在脉高3V、脉宽500ns的电脉冲下实现SET操作，在脉高4V、脉宽20ns的电脉冲下实现RESET操作，并能实现反复写/擦，而采用Ge₂Sb₂Te₅薄膜的相同结构的器件不能实现RESET操作. 关键词： 相变存储器 硫系化合物 2Te₃薄膜')" href="#">Si掺杂Sb₂Te₃薄膜 SET/RESET转变     

Transport coefficients and defect structure of Sb2−xAgxTe3 single crystals

Incorporation of Ag in the crystal lattice of Sb₂Te₃ creates structural defects that have a strong influence on the transport properties. Single crystals of Sb_2−xAg_xTe₃ (x=0.0; 0.014; 0.018 and 0.022) were characterized by measurements of the temperature dependence of the electrical resistivity, Hall coefficient, Seebeck coefficient and thermal conductivity in the temperature range of 5-300 K. With an increasing content of Ag the electrical resistance, the Hall coefficient and the Seebeck coefficient all decrease. This implies that the incorporation of Ag atoms in the Sb₂Te₃ crystal structure results in an increasing concentration of holes. However, the doping efficiency of Ag appears to be only about 50% of the expected value. We explain this discrepancy by a model based on the interaction of Ag impurity with the native defects in the Sb_2−xAg_xTe₃ crystal lattice. Defects have a particularly strong influence on the thermal conductivity. We analyze the temperature dependence of the lattice thermal conductivity in the context of the Debye model. Of the various phonon scattering contributions, the dominant influence of Ag incorporation in the crystal lattice of Sb₂Te₃ is revealed to be point-defect scattering where both the mass defect and elastic strain play a pivotal role.     

Electrodeposition of BixSb2−xTey thermoelectric thin films from nitric acid and hydrochloric acid systems

The electrochemical behaviors of Bi^III, Te^IV and Sb^III single ions and their mixtures were investigated in nitric acid and hydrochloric acid system separately. Based on which, Bi_xSb_2−xTe_y thermoelectric films were prepared by potentiostatic electrodeposition from the solutions with different concentrations of Bi^III, Te^IV and Sb^III in the two acid systems. The morphologies, compositions, structures, Seebeck coefficients and resistivities of the deposited thin films were characterized and compared by ESEM (or FESEM), EDS, XRD, Seebeck coefficient measurement system and four-probe resistivity measuring device respectively. The results show that although Bi_xSb_2−xTe_y thermoelectric thin film which structure is consistent with the standard pattern of Bi_0.5Sb_1.5Te₃ can be gained in both of the two acid solutions by adjusting the deposition potential, their morphologies and thermoelectric properties have big differences in different acid solutions.     

Effect of indium doping on Ge2Sb2Te5 thin films for phase-change optical storage

The influence of In doping on the crystallization kinetics of Ge₂Sb₂Te₅ has been investigated using four-point-probe electrical resistance measurements, grazing incidence X-ray diffraction (XRD), X-ray reflectometry (XRR), variable incident angle spectroscopic ellipsometry, a static tester, and atomic force microscopy. For a stoichiometric Ge₂Sb₂Te₅ alloy doped with 3% In, the amorphous-to-crystalline transition is observed at 150 °C in the sheet resistance measurements. XRD reveals the formation of a predominant NaCl-type Ge₂Sb₂Te₅ phase during the amorphous-to-crystalline transition together with small amounts of crystalline In₂Te₃. Density values of 5.88±0.05 g cm^-3 and 6.22±0.05 g cm^-3 are measured by XRR for the film in the amorphous and crystalline states, respectively. Perfect erasure can be achieved by laser pulses longer than 165 ns. The retarded crystallization, as compared with the undoped Ge₂Sb₂Te₅ alloy, is attributed to the observed phase segregation. Sufficient optical contrast is exhibited and can be correlated with the large density change upon crystallization. PACS 68.55.-a; 78.20.-e; 78.66.Jg     

应用于相变存储器的Cu-Ge3Sb2Te5薄膜的结构及相变特性研究

采用磁控溅射法制备了不同Cu含量的Cu-Ge₃Sb₂Te₅薄膜, 原位测试了薄膜电阻与温度的关系, 并利用X射线衍射仪、透射电镜、透过和拉曼光谱仪分别研究了 Cu-Ge₃Sb₂Te₅薄膜的晶体结构、微结构、禁带宽度及成键情况. 结果表明, Cu-Ge₃Sb₂Te₅薄膜的结晶温度和结晶活化能随着Cu含量的增加而增大, Cu的加入有效改善Ge₃Sb₂Te₅薄膜的热稳定性和10年数据保持力. 随着Cu含量的增加, 非晶态Cu-Ge₃Sb₂Te₅薄膜的禁带宽度逐渐减小. 同时, 拉曼峰从129 cm^-1向127 cm^-1处移动, 这是由于Cu–Te极性键振动增强的缘故. Cu-Ge₃Sb₂Te₅结晶为均匀、相互嵌套的六方Cu₂Te和Ge₂Sb₂Te₅相.     

Local atomic structure in molten Si3Sb2Te3 phase change material

By means of ab initio molecular dynamics calculations, we have studied the local structures of liquid and amorphous Si₃Sb₂Te₃. The results show that all the constitute elements in liquid Si₃Sb₂Te₃ are octahedrally coordinated. While in amorphous state, Sb and Te atoms are mainly octahedrally coordinated and Si atoms are mainly tetrahedrally coordinated. In both states, Si is mainly homo-bonded by Si. Finally, we proposed a phase separation model for liquid and amorphous Si₃Sb₂Te₃, which is responsible for the good performance of Si₃Sb₂Te₃ alloy as a phase change material.     

Phase stability and electronic structure of Si2Sb2Te5 phase-change material

On the basis of an ab initio computational study, the present work provide a full understanding on the atomic arrangements, phase stability as well as electronic structure of Si₂Sb₂Te₅, a newly synthesized phase-change material. The results show that Si₂Sb₂Te₅ tends to decompose into Si₁Sb₂Te₄ or Si₁Sb₄Te₇ or Sb₂Te₃, therefore, a nano-composite containing Si₁Sb₂Te₄, Si₁Sb₄Te₇ and Sb₂Te₃ may be self-generated from Si₂Sb₂Te₅. Hence Si₂Sb₂Te₅ based nano-composite is the real structure when Si₂Sb₂Te₅ is used in electronic memory applications. The present results agree well with the recent experimental work.     

Performance improvement of Sb2Te3 phase change material by Al doping

Al doped Sb₂Te₃ material was proposed to improve the performance of phase-change memory. Crystallization temperature, activation energy, and electrical resistance of the Al doped Sb₂Te₃ films increase markedly with the increasing of Al concentration. The additional Al-Sb and Al-Te bonds enhance the amorphous thermal stability of the material. Al_0.69Sb₂Te₃ material has a better data retention (10 years at 110 °C) than that of Ge₂Sb₂Te₅ material (10 years at 87 °C). With a 100 ns width voltage pulse, SET and RESET voltages of 1.3 and 3.3 V are achieved for the Al_0.69Sb₂Te₃ based device.     

Temperature dependence of the Raman spectra of Bi2Te3 and Bi0.5Sb1.5Te3 thermoelectric films

The temperature dependence of the Raman spectra of Bi₂Te₃ and Bi_0.5Sb_1.5Te₃ thermoelectric films was investigated. The temperature coefficients of the E_g(2) peak positions were determined as –0.0137 cm^–1/°C and –0.0156 cm^–1/°C, respectively. The thermal expansion of the crystal caused a linear shift of the Raman peak induced by the temperature change. Based on the linear relation, a reliable and noninvasive micro‐Raman scattering method was shown to measure the thermal conductivity of the thermoelectric films. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An analysis of the thermoelectric efficiency of n-(Bi,Sb)2(Te,Se,S)3 solid solutions within an isotropic scattering model

A study is reported on the thermoelectric properties of n-type solid solutions Bi₂Te_3?y Se_y (y=0.12, 0.3, 0.36), Bi_2?x Sb_xTe_3?y Se_y (x=0.08, 0.12; y=0.24, 0.36), and Bi₂Te_3?z S_z (z=0.12, 0.21) as functions of carrier concentration within the 80-to 300-K range. It has been established that the highest thermoelectric efficiency Z is observed in the Bi₂Te_3?y Se_y (y=0.3) solid solution containing excess Te at optimum carrier concentrations (0.35×10¹⁹ cm^?3) and at temperatures from 80 to 250 K. The increase in Z in the Bi₂Te_3?y Se_y solid solution compared with Bi_2?x Sb_xTe_3?y Se_y and Bi₂Te_3?z S_z is accounted for by the high mobility μ₀, an increase in the effective mass m/m ₀ with decreasing temperature, the low lattice heat conductivity κ_L, and the weak anisotropy of the constant-energy surface in a model assuming isotropic carrier scattering.