Low-temperature characterization and micropatterning of coevaporated Bi2Te3 and Sb2Te3 films

Abstract

Thermoelectric (TE) properties of the coevaporated Bi2Te3 and Sb2Te3 films are measured from 100 to 300 K for Seebeck coefficient αS and from 5 to 300 K for electrical resistivity ρe, mobility μe, and Hall coefficient RH. For the low-temperature characterization of TE films, the conditions for coevaporation deposition of Bi, Te, and Sb to form Bi2Te3 and Sb2Te3 films are also investigated, including substrate material, substrate temperature Tsub, and elemental flux ratio (FR). The resublimation of Te occurring above 473 K significantly affects the film composition and quality. Our optimal deposition conditions for Bi2Te3 films are Tsub=533 K and FR=2.4, and those for Sb2Te3 films are Tsub=503 K and FR=3.0. The TE properties of both films are strongly temperature dependent, while Bi2Te3 films show a stronger temperature dependence than Sb2Te3 films due to different major scattering mechanisms. αS of both the coevaporated films are close to or higher than those of bulk materials, but ρe is much higher (due to lower carrier concentrations for Sb2Te3 films and lower μe for Bi2Te3 films). Also, no freeze-out regime is found for both Bi2Te3 and Sb2Te3 films at low temperatures. The room-temperature power factors of αS2/ρe for Bi2Te3 and Sb2Te3 films are 2.3 and 2.0 mW/K2 m, and the maxima are 2.7 mW/K2 m for Bi2Te3 at T=220 K and 2.1 mW/K2 m for Sb2Te3 at T=280 K. Shadow mask technique is successfully used for the micropatterning (20 μm) of TE films with no significant change in properties.

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

“…The texture in the annealed thin films was analyzed by high-energy XRD in transmission and grazing incidence geometry and by electron diffraction on TEM cross sections. Particularly, highenergy XRD yielded a complete insight into texture of the films and epitaxial relations to the substrate and, to our knowledge, was not shown before by any other groups [3][4][5][6][7][8][9][10][11][12].…”

“…In Table 5 [6]. Finally, results of a previous MBE study of epitaxially grown Bi 2 Te 3 thin films were included in Table 5 [4,5].…”

“…For MBE growth of Bi 2 Te 3 and Sb 2 Te 3 films substrate temperatures in the range of 225-350 • C are used (Table 5) [4][5][6][7][8][9][10][11][12]. In a previous study of epitaxially grown Bi 2 Te 3 thin films an optimum substrate temperature of T S = 290 • C and a flux ratio F R = Te/Bi = 12/5 was found [4,5,22].…”

A Study on Sputtered Bi-Te Thermoelectric Films with Various Compositions: Microstructure Evolution and the Effects on Thermoelectric and Electrical Properties

“…Recently, several studies have reported significant advances in improving thermoelectric properties using TE devices built with Bi-Te-based thin films, fueling research interest in these thermoelectric thin films. [3][4][5] Among several compounds (Bi 4 Te 3 , BiTe, Bi 2 Te 3 , etc.) of Bi-Te alloys, 6,7 only Bi 2 Te 3 is known to have a Seebeck coefficient value suitable for thermoelectric applications.…”

Preparation and thermoelectric properties of p-type Bi0.52Sb1.48Te3 + 3% Te thin films

“…Lowdimensional Bi 2 Te 3 -based materials, which show special quantum confinement effects and electrical transport properties [4], have proved to be an effective route for improving thermoelectric properties [5]. Many deposition methods have been used to prepare Bi 2 Te 3 -based thin films; these include co-evaporation [6,7], metal organic chemical vapor deposition [8], pulsed laser deposition [9,10], electrochemical deposition [11,12], electrochemical atomic layer epitaxy [13,14], molecular beam epitaxy [15], co-sputtering [16], closed space vapor transport techniques [17], hotwall-epitaxy techniques, and electron-beam evaporation [18]. In this work, because of the simple configuration of the deposition system, we use a flash evaporation method [19][20][21][22] for the fabrication of Bi 2 Te 3 -based alloy thin films.…”