Surface versus bulk electronic/defect structures of transparent conducting oxides: I. Indium oxide and ITO

Carefully prepared bulk ceramic specimens of In₂O₃ and Sn-doped In₂O₃ (ITO) were analysed with x-ray and UV photoelectron spectroscopy before and after heat treatment in vacuum and oxygen atmosphere. The results on ex situ prepared ceramic specimens were shown to be comparable to those of in situ deposited-measured thin films in terms of core levels, Fermi levels and ionization potentials. This suggests a viable path for rapid synthesis and screening of surface electronic-defect properties for other transparent conducting oxides (TCO) materials. A strong correlation exists between the surface electronic-defect structure of In₂O ₃-based TCOs and their underlying electronic-defect structure, owing to the unique crystal-defect properties of the bixbyite structure. This leads to formation of a chemical depletion at the surface and the formation of a peroxide surface species for higher preparation temperatures. The results are discussed with respect to the use of ITO as hole injection electrode in organic light emitting devices.