Structural, electrical and optical properties of sputtered vanadium pentoxide thin films

Abstract

Thin films of vanadium pentoxide (V 2O 5) are prepared by r.f. sputtering from a V 2O 5 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 V 2O 5 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 o (value for bulk V 2O 5), and to increase with increasing sputtering gas O 2 content. The thermally induced reduction under vacuum of V 2O 5 into a VO 2 occurs at about 400 °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.