Vapor Annealing as a Post-Processing Technique to Control Carrier Concentrations of Bi2Te3 Thin Films

Abstract

This article demonstrates that carrier concentrations in bismuth telluride films can be controlled through annealing in controlled vapor pressures of tellurium. For the bismuth telluride source with a small excess of tellurium, all the films reached a steady state carrier concentration of 4 9 10 19 carriers/cm 3 with Seebeck coefficients of À170 lV K À1 . For temperatures below 300°C and for film thicknesses of 0.4 lm or less, the rate-limiting step in reaching a steady state for the carrier concentration appeared to be the mass transport of tellurium through the gas phase. At higher temperatures, with the resulting higher pressures of tellurium or for thicker films, it was expected that mass transport through the solid would become rate limiting. The mobility also changed with annealing, but at a rate different from that of the carrier concentration, perhaps as a consequence of the non-equilibrium concentration of defects trapped in the films studied by the low temperature synthesis approach.

Assessing Antisite Defect and Impurity Concentrations in Bi2Te3 Based Thin Films by High‐Accuracy Chemical Analysis

“…Bulk materials with Bi excess yield p‐type conduction (Figure 4),1, 15 which is explained by acceptor‐like Bi Te antisites 16. However, in the series of Bi‐Te thin films with Bi excess investigated here only n‐type conduction was observed, which is in agreement with similar reports 5, 9, 10, 31. The chemical analysis of such films revealed about 7 at% oxygen in some Bi‐Te films (samples 2 and 3), which might explain their n‐type character.…”

Bi2Te3-Sb2Te3 Superlattices Grown by Nanoalloying

“…7 Our result is also in accordance with a study by Nurnus et al, 8 who achieved only n-type epitaxial layers of Bi 2 Te 3 . A possible reason may be the formation of Bi precipitates or a Bi 2 -Bi 2 Te 3 layered structure instead of Bi antisite defects.…”

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

“…A sticking coefficient K S (Te) = 0.6 was obtained for T S = 310 • C and F R = 2 [14]. As an alternative approach, room-temperature MBE together with a subsequent annealing step was found as a promising route [15,17] to obtain thin films with controlled stoichiometry as demonstrated in this work ( Table 2). As-deposited Sb 2 Te 3 films yielded pronounced X-ray reflections with spacings only compatible with {0 0 l} reflections of the Sb 2 Te 3 structure.…”

“…9(a) and (b) a TEM bright-field image and a corresponding RGB map are shown, respectively. The RGB map was obtained by superposition of three energy-filtered images for energy-losses of 17,25 (=Bi O 4,5 ), and 17 eV, respectively. As confirmed by EDX, in the RGB map green regions turned out to be Bi-rich grain boundary phases whereas the Bi 2 Te 3 matrix of the film is in purple ( Fig.…”