STRUCTURAL, ELECTRICAL AND OPTICAL-PROPERTIES OF SPUTTERED VANADIUM PENTOXIDE THIN-FILMS

Thin films of vanadium pentoxide (V2O5) are prepared by r.f. sputtering from a V2O5 target in a gas mixture of argon and oxygen under a total pressure P-t=P(O-2)+P(Ar)=10(-2) mbar. The P(O-2)/P-t partial pressures ratio is changed from 0% to 20%. Investigations by X-ray diffraction measurements (XRD), by infrared (IR), Raman and X-ray photoelectron (XPS) spectroscopies, by conductivity measurements and by optical transmission spectroscopy are made in order to determine the structural, electrical and optical properties of V2O5 thin films. All the films grown under oxygen partial pressure are identified as vanadium pentoxide. Their polycrystalline texture is such that the (001)-type planes lie parallel to the substrate. The average (001) interplanar spacing c is found to be greater than c(0) (value for bulk V2O5), and to increase with increasing sputtering gas O-2 content. The thermally induced reduction under vacuum of V2O5 into a VO2 occurs at about 400 degrees C. On the other hand, the treatment of electrical conductivity is made on the basis of Mott and Austin's theories. Finally, the optical constants and thickness of the films are calculated using a simple and accurate method based on the transmission spectrum alone and taking into account thickness inhomogeneities in the sputtered films.