The electronic properties and defect chemistry of Bi2-xSe3, –0.05

Abstract

The Hall effect, temperature dependent resistivity, and optical spectroscopy (4.3 meV–6.2 eV) of a series of Bi2-xSe3 crystals in the range −0.05 < x < 0.15, have been measured. We find that Bi2-xSe3, grown directly from a melt, is a narrow band gap degenerate semiconductor where the carrier concentration varies in a systematic, although non-monotonic way, with the Bi melt-content. We have successfully modelled the compositional dependency of the carrier concentration using theoretical estimates of the defect formation energies. We found both Se vacancies and Se on the Bi site (SeBi anti-site) defects are the main contributors of carriers (electrons), with Se vacancies dominant at high Bi melt content and SeBi anti-site defects favoured at high Se melt content. The data indicates that an effective approach to reducing the carrier concentration in Bi2Se3 is by compensation using atomic substitution, or, preferably growth by low-temperature, non-equilibrium methods.