Huge Photoresistance in Transparent and Conductive Indium Titanium Oxide Films Prepared by Electron Beam–Physical Vapor Deposition

Transparent and conductive indium titanium oxide (ITiO) films have been obtained by electron beam physical vapour deposition with Ti content from 5 at % up to 28 at %. X-ray absorption spectroscopy techniques have been used to identify the local environment of Ti ions. Even at the lowest concentrations Ti is not incorporated into the In2O3 structure but forms clusters of a Ti-In mixed oxide that present a distorted rutile TiO2 short-range order. The optical transmittance of the annealed samples reaches 95 % and no significant variation of the gap energy (around 3.7 eV) is observed with Ti content. The electronic conductivity under light irradiation is studied evidencing a huge photo-resistance in the samples with Ti content above 22 at % reaching more than two orders of magnitude for the 26 at % Ti under illumination with few μW/cm(2) at 365 nm. Hall and conductivity results are analyzed using a model that takes into account both electron and hole carriers as well as the conductivity enhancement by carrier photogeneration. The electron carrier density decreases with Ti content while its mobility increases up to values of 1000 cm(2)/(V s). Oxygen annealed ITiO films obtained by this technique with Ti content below 10 at % have properties adequate as transparent semiconductors and those with Ti content higher than 22 at % have exceptional photoresistive properties relevant for numerous applications.