Effect of oxygen on transient photoconductivity in thin-filmNbxTi1−xO2

Transient photoconductivity in thin-film ${\mathrm{Nb}}_x{\mathrm{Ti}}_{1-x}{\mathrm{O}}_2$ and ${\mathrm{TiO}}_2$ was studied as a function of temperature, light intensity, illumination time, and ambient composition in a time range of ${10}^{-2}–{10}^7\mathrm{s}.$ Both excitation and relaxation transients were slow and followed a nonexponential rate law. A conductivity model predominantly involving hole capture by ${\mathrm{O}}_2^{\mathrm{-}}$ at the surface is proposed. It was possible to use a Laplace transform method to determine the free electron density and the photoinduced change in the surface barrier caused by hole capture at the surface. In argon, both the oxygen adsorption rate and the rate at which excess electrons reach the surface may contribute to the decay whereas only the latter may be important in air.