Thickness and growth-condition dependence of in-situ mobility and carrier density of epitaxial thin-film Bi₂Se₃

Bismuth selenide Bi₂Se₃ was grown by molecular beam epitaxy, while carrier density and mobility were measured directly in situ as a function of film thickness. Carrier density shows high interface n-doping (1.5 × 10¹³cm⁻²) at the onset of film conduction and bulk dopant density of ∼5 × 10¹¹cm⁻² per quintuple-layer unit, roughly independent of growth temperature profile. Mobility depends more strongly on the growth temperature and is related to the crystalline quality of the samples quantified by ex-situ atomic force microscopy measurements. These results indicate that Bi₂Se₃ as prepared by widely employed parameters is n-doped before exposure to atmosphere, the doping is largely interfacial in origin, and dopants are not the limiting disorder in present Bi₂Se₃ films.