The effect of substrate bias on the electrical and optical properties of In2O3 films grown by RF sputtering

Partially degenerate n-type semiconducting films of In2O3 which are transparent in the visible spectrum have been grown on Corning 7059 glass substrates by rf sputtering. The films ranged in thickness from 0.25 to 1.5 μm and are deposited in Ar at a pressure of 15 m Torr (2 Pa) with a target voltage of −750 V. It is found that both the electrical and optical properties of as-deposited films depend strongly on the applied negative substrate bias Us. Film carrier concentration, n, reaches a minimum of 1 × 1020 cm−3 at Us = −25 V while the electron mobility increases continuously with negative substrate biases up to 60 V. Films with high values of n exhibit free carrier absorption effects in the visible and infrared regions of the spectrum. A smearing out of the valence band edge is observed in all films, with the degree of band tailing decreasing with increasingly negative values of Us. Annealing the films at 400°C tends to diminish differences in as-deposited film properties.