Preparation of clean Bi2Te3 and Sb2Te3 thin films to determine alignment at valence band maxima

The thermoelectric application of Bi2Te3 and Sb2Te3 thin film structures relies on the relative alignment of the valence band maxima for good electrical conduction. In order to determine the valence band maxima of the bulk films, the authors propose a simple repeatable treatment of a chemical etching in dilute hydrochloric acid solution and a subsequent annealing at ∼150 °C under ultrahigh vacuum to prepare clean surfaces of Bi2Te3 and Sb2Te3 thin films. High-resolution photoemission spectroscopy using synchrotron radiation is used to investigate the chemical states of epitaxial Bi2Te3 and Sb2Te3 thin films grown on GaAs by low-temperature metal-organic chemical vapor deposition. The valence band and core-level photoemission spectra indicate that the surface contaminations and oxides were removed. After chemical etching in acid solution, elemental Te was observed on the surface; a follow-up anneal in ultrahigh vacuum creates a stoichiometric oxide-free surface.