The bulk and surface electronic structure of In 2 O 3 has proved controversial, prompting the current combined experimental and theoretical investigation. The band gap of single-crystalline In 2 O 3 is determined as 2.93Ϯ 0.15 and 3.02Ϯ 0.15 eV for the cubic bixbyite and rhombohedral polymorphs, respectively. The valence-band density of states is investigated from x-ray photoemission spectroscopy measurements and density-functional theory calculations. These show excellent agreement, supporting the absence of any significant indirect nature of the In 2 O 3 band gap. Clear experimental evidence for an s-d coupling between In 4d and O 2s derived states is also observed. Electron accumulation, recently reported at the ͑001͒ surface of bixbyite material, is also shown to be present at the bixbyite ͑111͒ surface and the ͑0001͒ surface of rhombohedral In 2 O 3 .

We report on the phase stabilization of rhombohedral (rh-) In 2 O 3 films on sapphire substrate deposited by metal organic chemical vapor deposition. With the help of a high-temperature nucleation layer and evolutionary structural selection of rhombohedral phase during the growth process, stable epitaxial growth of single crystalline rh-In 2 O 3 is achieved. The mechanism of phase selective epitaxial growth is studied by means of high-resolution X-ray diffraction and transmission electron microscopy measurements. Furthermore, Raman spectroscopy measurements are carried out to investigate the phonon properties of rh-In 2 O 3 . Raman-active phonon modes of rh-In 2 O 3 are first identified.

Phase selective growth of rhombohedral and cubic indium oxide polytypes was studied. The selective growth of different polytypes was achieved by adjusting substrate temperature and trimethylindium flow rate during metal organic chemical vapor deposition on c-plane sapphire. The optical band gaps of the cubic and rhombohedral phases were determined to be ∼3.7 and ∼3.0eV, respectively. On the basis of the performed structural investigations, a phenomenological model of the nucleation and growth of highly textured cubic In2O3 on Al2O3 (0001) is proposed.

No abstract