Electrical and optical properties of r.f.-sputtered amorphous V2O5-CaO-MoO3 films

Amorphous films of the V2O5-CaO-MoO3 system are fabricated by r.f.-sputtering and the d.c. conductivity and optical properties are studied. The conductivity of 1200–1400 nm thick amorphous V2O5-CaO-MoO3 films with different film compositions ranges from 4.7 × 10−4 to 1.1 S cm−1 at 458 K. The films are n-type semiconducting. The conduction of the films is attributed to adiabatic small polaron hopping and is primarily due to hopping between V4+ and V5+ ions. The films are optically transparent in the visible range. The optical band gap energy is evaluated to be between 2.90 and 2.39 eV. The Urbach tail analysis gives the width of localized states between 0.40 and 0.58 eV. A feasibility study reveals the films to be applicable as transparent film thermistors.