Electrical and optical properties of reactively sputtered tungsten oxide films

Abstract

Electrical and optical properties of reactively sputtered tungsten oxide films have been investigated in relation to the oxygen concentration in sputtering atmosphere. The films with 5200–6600 Å thick were prepared under a constant pressure of 5×10−3 Torr using a mixture of Ar and 4–50% O2. Electrical resistivity and spectral transmittance of the films formed depend extremely on the oxygen concentration in the atmosphere. The films formed in an atmosphere containing less than 13% O2 are semiconductive, have a resistivity of 10−3–103 Ω cm, and are blue colored. The films formed in an atmosphere containing more than 16% O2 are transparent and have a resistivity of 107–1011 Ω cm. Optical band gap of the films formed under a sputtering atmosphere containing 8–50% O2 is almost constant and ranges 3.00–3.03 eV. The carrier concentration and Hall mobility of semiconductive films and the refractive index of insulating films were also measured. The presence of a critical oxygen concentration for the formation of either semiconductive or insulating films has been suggested.