On the Origin of the Bandshifts in the Action Spectra of Polycrystalline TiO2 Electrodes Prepared by Thermal Oxidation of Titanium

Abstract

The spectral distribution of the quantum efficiency in the range 250–550 nm has been determined for a number of electrodes prepared by thermal oxidation in air (temperature range 500°–700°C). A red shift in the action spectra and an extensive decrease in the quantum efficiency in the short wavelength range (250–300 nm) were observed with increasing oxidation. The effect of different polishing procedures on the electrodes before and after the formation of the layers was also investigated. A marked increase in quantum efficiency, especially in the short wavelength range, was registered with increasing surface finish of the electrodes. The observed changes in the action spectra are discussed in terms of electron‐hole recombination mediated via surface states and recombination in the rough surface. It was possible to describe the registered action spectra in the wavelength range 300–400 nm in terms of the known absorption coefficient and a modified Gärtner‐Butler equation with three adjustable parameters. The experimental data also give evidence of a gradient in doping density normal to the surface of the layer electrodes.