Effect of oxygen on transient photoconductivity in thin-film NbxTi1-xO2

Transient photoconductivity in thin-film NbxTi1-xO2 and TiO2 was studied as a function of temperature, light intensity, illumination time, and ambient composition in a time range of 10(-2)-10(7) s. Both excitation and relaxat ion transients were slow and followed a nonexponential rate law. A conducti vity model predominantly involving hole capture by O-2(-) at the surface is proposed. It was possible to use a Laplace transform method to determine t he free electron density and the photoinduced change in the surface barrier caused by hole capture at the surface. In argon, both the oxygen adsorptio n rate and the rate at which excess electrons reach the surface may contrib ute to the decay whereas only the latter may be important in air.