Annealing effects on the structural and optical properties of vanadium oxide film obtained by the hot-filament metal oxide deposition technique (HFMOD)

Abstract

Vanadium oxide films amorphous, nonstoichiometric and highly absorbing in the optical region were deposited
on ITO-coated glass and on silicon substrates, by the hot-filament metal oxide deposition technique
(HFMOD) and oxidized by ex-situ annealing in a furnace at 200, 300, 400 and 500 ºC, under an atmosphere
of argon and rarefied oxygen. X-ray diffraction, Raman and Rutherford backscattering spectroscopy as well
as optical transmission were employed to characterize the amorphous and annealed films. When annealed at
200 and 300 ºC the as-deposited opaque films become transparent but still amorphous. Under treatments at
400 and 500 ºC a crystalline nonstoichiometric V2O5 structure is formed. All the annealed films became semiconducting,
with their optical absorption coefficients changing with the annealing temperature. An optical
gap of 2.25 eV was measured for the films annealed at 400 and 500 ºC. The annealing in rarefied oxygen
atmosphere proved to be a useful and simple ex-situ method to modulate the structural and optical properties
of vanadium oxide films deposited by HFMOD technique. This technique could be applied to other amorphous
and non-absorbing oxide films, replacing the conventional and sometimes expensive method of modulate
desirable film properties by controlling the film deposition parameters. Even more, the HFMOD technique
can be an inexpensive alternative to deposit metal oxide films.