Electronic structure of VO2/TiO2:Nb upon photocarrier injection

We study the photocarrier injected electronic structure of VO2/TiO2:Nb (equivalent to p-n junction) thin-film heterostructure using photoemission spectroscopy, across the temperature-dependent metal-insulator transition in VO2. The valence band of VO2 shifts systematically to higher binding energy upon photocarrier injection (PCI). In the insulating phase, the energy shift as a function of irradiated power matches the surface photovoltage (SPV) behavior, while in the metallic phase, the energy shift follows the SPV trend but is reduced due to recombination. The temperature dependence of the energy shift between 200 and 330 K varies nearly linearly with the SPV. The study provides evidence for hole doping from TiO2:Nb to VO2 by the PCI effect.