Photocarrier injection to transition metal oxides

An efficient and clean method of doping transition metal oxides (TMOs) with hole carriers is presented. We have fabricated oxide heterostructures made of various TMO thin films grown on n-type titanium oxide substrates, and measured in-plane resistance under ultraviolet light irradiation. It is shown that the resistance of the insulating TMOs is reduced significantly with increasing light irradiance, as a result of photoinduced hole carrier injection from the titanium oxide substrates. A generic band structure for the heterojunctions is proposed, in which a large potential slope and a small barrier exist near the interface for photoinduced holes and electrons in the titanium oxides, respectively. This photocarrier injection (PCI) technique would provide us with a useful method to achieve the external control of hole carrier density in TMOs.