Native defects in tetradymite Bi2(TexSe3-x) topological insulators.

Formation energies of native defects in Bi2(TexSe3?x), with comparison to ideal Bi2Te2S, are calculated in density-functional theory to assess transport properties. Bi2Se3 is found to be n type for both Bi- and Se -rich growth conditions, while Bi2Te3 changes from n to p type going from Te- to Bi-rich conditions, as observed. Bi2Te2Se and Bi2Te2S are generally n type, explaining observed heavily doped n-type behavior in most samples. A (0/?) transition level at 16 meV above valence-band maximum for Bi on Te antisites in Bi2Te2Se is related to the observed thermally active transport gap causing a p-to-n transition at low temperature. Bi2(TexSe3?x) with x>2 are predicted to have high bulk resistivity due to effective carrier compensation when approaching the n-to-p crossover. Predicted behaviors are confirmed from characterization of our grown single crystals. [ABSTRACT FROM AUTHOR]