Surface electronic properties of polycrystalline bulk and thin film In2O3(ZnO)k compounds

Highlights: ► Indium zinc oxide compounds for TCO applications. ► Surface energy levels studied by XPS, UPS, and Kelvin probe. ► Ionization potential was constant for all compounds measured. ► Ionization potential, work function, and Fermi levels similar to In2O3 and ZnO. - Abstract: The surface electronic potentials of In2O3(ZnO)k compounds were measured by X-ray and ultraviolet photoelectron spectroscopy. Both thin film (k = 2) and bulk specimens (k = 3, 5, 7, 9) were studied. All bulk specimens exhibited In enrichment at the surface. All samples showed an increase of In core level binding energies compared to pure and Sn-doped In2O3. The work functions and Fermi levels spanned a range similar to those of the basis oxides In2O3 and ZnO, and the ionization potential was similar to that of both In2O3 and ZnO processed under similar conditions (7.7 eV). This ionization potential was independent of both composition and post-deposition oxidation and reduction treatments. Kelvin probe measurements of cleaned and UV-ozone treated specimens under ambient conditions were in agreement with the photoelectron spectroscopy measurements.