Bulk and surface characterization of In2O3(001) single crystals

D. R. Hagleitner1, M. Menhart1, P. Jacobson1, S. Blomberg2, K. Schulte2, E. Lundgren2, M. Kubicek3 J. Fleig3, F. Kubel3, C. Puls3, Andreas Limbeck3, H. Hutter3, L. A. Boatner4, M. Schmid1, U. Diebold1

1 Institut für Angewandte Physik, Technische Universität Wien, 1040 Wien, Austria
2 Division of Synchrotron Radiation Research, Lund University, SE 22100 Lund, Sweden
3 Institute of Chemical Technologies and Analytics, TU Wien, 1060 Wien, Austria
4 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

Phys. Rev. B 85 (2012) 115441

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. Inductively coupled plasma mass spectrometry (ICP-MS) reveals small residues of Pb, Mg, and Pt in the crystals. Four-point-probe measurements show a resistivity of 2.0 ± 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) and oxidized (exposure to atomic oxygen at 300 °C) surface show a step height of 5 Å, which indicates a preference for one type of surface termination. The surfaces stay flat without any evidence for macroscopic faceting under any of these preparation conditions. 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 under reducing conditions, with a surface structure corresponding to a strongly distorted indium lattice. Scanning tunneling spectroscopy (STS) reveals a pronounced surface state at the Fermi level. Photoelectron spectroscopy (PES) shows additional, deep-lying band gap states, which can be removed by exposure of the surface to atomic 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 is observed for the reduced surface, while the band bending of the oxidized surface is of the order of 0.1 eV or less.

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