Room-temperature MBE deposition, thermoelectric properties, and advanced structural characterization of binary Bi₂Te₃ and Sb₂Te₃ thin films

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• 作者：N. Peranio^a ; ^{nicola.peranio@uni-tuebingen.de} ; M. Winkler^b ; D. Bessas^c ; ^d ; Z. Aabdin^a ; J. Kö ; nig^b ; H. Bö ; ttner^b ; R.P. Hermann^c ; ^d ; O. Eibl^a
• 关键词：Thermoelectric materials ; Vapor deposition ; X-ray diffraction ; Transmission electron microscopy ; Microstructure ; Composition fluctuations
• 刊名：Journal of Alloys and Compounds
• 出版年：2012
• 期刊代码：45_09258388
• 类别：ms
• 出版时间：25 April, 2012
• 卷：521
• 期：Complete
• 页码：163-173
• 文件大小：2116 K

摘要

Sb₂Te₃ and Bi₂Te₃ thin films were grown at room temperature on SiO₂ and BaF₂ substrates using molecular beam epitaxy. A layer-by-layer growth was achieved such that metallic layers of the elements with 0.2 nm thickness were deposited. The layer structure in the as-deposited films was confirmed by X-ray diffraction and was seen more clearly in Sb₂Te₃ thin films. Subsequent annealing was done at 250 掳C for 2 h and produced the Sb₂Te₃ and Bi₂Te₃ crystal structure as confirmed by high-energy X-ray diffraction. This preparation process is referred to as nano-alloying and it was demonstrated to yield single-phase thin films of these compounds. In the thin films a significant texture could be identified with the crystal c axis being almost parallel to the growth direction for Sb₂Te₃ and tilted by about 30掳 for Bi₂Te₃ thin films. In-plane transport properties were measured for the annealed films at room temperature. Both films yielded a charge carrier density of about 2.6 脳 10¹⁹ cm^鈭?. The Sb₂Te₃ films were p-type, had a thermopower of +130 渭V K^鈭?, and surprisingly high mobilities of 402 cm² V^鈭? s^鈭?. The Bi₂Te₃ films were n-type, showed a thermopower of 鈭?53 渭V K^鈭?, and yielded significantly smaller mobilities of 80 cm² V^鈭? s^鈭?. The chemical composition and microstructure of the films were investigated by transmission electron microscopy (TEM) on cross sections of the thin films. The grain sizes were about 500 nm for the Sb₂Te₃ and 250 nm for the Bi₂Te₃ films. In the Bi₂Te₃ thin film, energy-filtered TEM allowed to image a Bi-rich grain boundary phase, several nanometers thick. This secondary phase explains the poor mobilities of the Bi₂Te₃ thin film. With these results the high potential of the nano-alloying deposition technique for growing films with a more complex layer architecture is demonstrated.