Efficiency of Photocarrier Injection in a VO₂/TiO₂:Nb Heterostructure

Abstract

The efficiency of photocarrier injection in a VO₂/TiO₂:Nb heterostructure is studied by measuring I–V characteristics at room temperature under ultraviolet light irradiation. It is revealed that photogenerated hole carriers in the TiO₂:Nb substrate are injected and accumulated in the VO₂ film by the photovoltaic effect. The surface charge density is controlled successfully in a wide range of 10⁹–10¹³ cm⁻² as a function of light irradiance. The maximum hole density of 9×10¹⁸ cm⁻³ is attained at a light irradiance of 133 mW/cm², which is estimated by assuming the uniform distribution of holes in the film. It is suggested that high efficiency can be achieved by utilizing the large dielectric constant of titanium oxide substrates.