Bulk and surface characterization of In2O3(001) single crystal

Abstract

A comprehensive bulk and surface investigation of high-quality In2O3(001) single crystals is reported. The transparent-yellow, cube-shaped single crystals were grown using the flux method. ICP-MS measurements reveal small residues of Pb, Mg and Pt in the crystals. Four-point-probe measurements show a resistivity of 2 ± 0.5  105 Ω cm, which translates into a carrier concentration of ≲ 1012 cm-3. The results from X-ray diffraction (XRD) measurements revise the lattice constant to 10.1150(5) Å from the previously accepted value of 10.117 Å. Scanning Tunneling Microscopy (STM) images of a reduced (sputtered/annealed) surface show a step height of 5 Å, which indicates a preference for one type of surface termination. A combination of low-energy ion scattering (LEIS) and atomically resolved STM indicates an indium-terminated surface with small islands of 2.5 Å height, which corresponds to a strongly distorted indium lattice. Scanning Tunneling Spectroscopy (STS) reveals a pronounced surface state at the Fermi Level (EF). Photoelectron Spectroscopy (PES) shows additional, deep-lying band gap states, which can be removed by exposure of the surface to activated oxygen. Oxidation also results in a shoulder at the O 1s core level at a higher binding energy, possibly indicative of a surface peroxide species. A downward band bending of 0.4 eV and an upward band bending of ~0.1 eV is observed for the reduced and oxidized surfaces, respectively.