Optical properties of In₂O₃ thin films prepared by rf helicon magnetron sputtering

Polycrystalline In₂O₃ films with cubic crystal structure and film thicknesses of 239, 472, 579 and 745 nm respectively were grown on quartz substrates at substrate temperature 450 °C by rf helicon magnetron sputtering. The preferred crystal growth orientation is varied from <111> to <211> with increasing film thickness as confirmed by X-ray diffractometry. The photon energy dependent optical properties such as complex dielectric functions and absorption coefficient, optical band gap, and Urbach energy width of the samples have been obtained from spectroscopic ellipsometry analysis in the energy range from 1.5 eV to 5.0 eV. The relation between those optical properties and crystal structure and/or crystallinity of the films was discussed. The band gap value, which is averaged over two typical samples with good crystallinity, is 3.765 eV and agrees satisfactorily with reported value on that of single crystal.