High-quality transparent conductive indium oxide films prepared by thermal evaporation

Abstract

Highly transparent (over 90% transmission in the visible range) and highly conductive (resistivity ≃2×10−4 Ω cm) indium oxide (undoped) films have been produced by thermal evaporation from an In+In2O3 source in a vacuum chamber containing low pressures of O2. These properties are comparable or superior to the best tin-doped indium oxide films ever reported, and excellent reproducibility has been achieved. Hall effect measurements have revealed that the observed low resistivity is primarily a result of the excellent electron mobility (≃70 cm2/V sec), although the electron concentration is also rather high (⩾4×1020/cm3). X-ray diffraction measurements show distinctly polycrystalline In2O3 structure with a lattice constant ranging from 10.07 to 10.11 Å. Electrolytic electroreflectance spectra exhibit at least four critical transitions, from which we have determined the direct and indirect optical band gaps (≃3.56 and 2.69 eV, respectively). Burstein shifts due to the population of electrons in the conduction band are also observed. These and other results along with a discussion of the processing details are reported.