Surface and bulk properties of sputter deposited undoped and Sb-doped SnO2 thin films

Electronic surface and bulk properties of sputter deposited polycrystalline intrinsic and Sb-doped SnO2 thin films have been investigated by a combination of in situ   photoelectron spectroscopy, electrical four-point conductivity, and optical transmission measurements. The work function and ionization potential of the polycrystalline films increase with increasing oxygen content in the sputter gas by ∼1.4∼1.4 and ∼1∼1 eV, respectively. The changes are explained by the different surface terminations known for single crystalline SnO2. Comparison of surface and bulk Fermi level positions indicates flat band situation for most cases but the presence of a depletion layer for Sb-doped films deposited under oxidizing conditions. Large changes of electrical conductivity depending on the oxygen content in the sputter gas were observed for undoped SnO2 which can be understood in terms of different concentrations of oxygen vacancies. In contrast, literally no changes occur for SnO2:Sb, which is attributed to the too high formation energy of compensating defects like oxygen interstitials or Sn vacancies.