A simple growth method for Nb2O5 films and their optical properties

A simple method for the synthesis of Nb2O5 films of thicknesses ranging from tens to several hundreds of nanometers on amorphous silicon dioxide or quartz substrates is presented. Nb2O5 films were formed by annealing the sputter deposited Nb films under an Ar flow and without oxygen plasma in a quartz tube within a furnace at 850 C. The structural, compositional, optical, and vibrational properties were characterized by grazing incidence X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet visible spectroscopy, and Raman scattering. Each of the Nb2O5 films is polycrystalline with an orthorhombic crystal structure. We observed vibrational modes including longitudinal optical, transverse optical, and triply degenerate modes, and measured the indirect optical band gap to be 3.65 eV. The transmittance spectrum of the 20 nm thick Nb2O5 film shows over 90% transmittance below the band gap energy in the visible wavelength range and decreases to less than 20% in the ultraviolet regime. The optical properties of the films in the UV-vis range show potential applications as UV detectors.