Composition-dependent layered structure and transport properties in BiTe thin films

We have studied the compositional dependence of the layered structure of ${\mathrm{Bi}}_{1+x}{\mathrm{Te}}_{1\ensuremath{-}x}$ thin films and its relation with the transport properties. We have observed that the ${\mathrm{Bi}}_{1+x}{\mathrm{Te}}_{1\ensuremath{-}x}$ films have a stable structure near the ${\mathrm{Bi}}_{1}{\mathrm{Te}}_{1}$ composition and that their crystallinity depends strongly upon the compositional deviation from stoichiometric ${\mathrm{Bi}}_{1}{\mathrm{Te}}_{1}.$ We have determined possible layered structures, configured with two sequences of Bi--Bi and Te--Bi--Te--Bi--Te, corresponding to Bi and Te binary compositions using x-ray diffraction analysis. Their c-axis lattice constants were in the range of 36 \AA{} and 136 \AA{}. Temperature-dependent thermopowers of the films reveal that as the composition changes from Te rich to Bi rich, the polarity varies from n type to p type.