Intermediate pinning states engineering in Bi-doped SnO2 for transparent semi-insulator applications

Bi-doped SnO2 (BTO) thin films were prepared by the magnetron reactive sputtering technique. The BTO thin films were characterized by x-ray photoelectron core level and valence band spectroscopy. Bi was introduced into an SnO2 lattice dominated with Bi5+ states accompanied with Bi3+ minority states. The BTO films exhibited a high optical transparency (>85% @550 nm) in the whole range of solar radiation spectrum without compromising the band gap alignment. The sheet resistance dramatically increased up to 108 Ω/sq after Bi doping. The reduction of electron concentration can be attributed to the electrons pinning to the intermediate state within the band gap. The BTO films have promising applications in high performance optoelectronic and photovoltaic devices.