Fine Structures of Conduction and Intermediate Bands of NaBiO3•2H2O/NaBiO3•xH2O Heterostructures Investigated by Surface Photovoltage Measurement with External Bias

The fine structures of conduction and intermediate bands of semiconductors determine photoelectronic properties of devices, whose investigation is developed with surface photovoltage(SPV) measurement. With external bias, the differences of SPV intensities at 400 and 375 nm of NaBiO3•2H2O/NaBiO3•xH2O heterostructures increase with temperature and reach the maximum for the sample heated at about 110 °C. The SPV at about 470 nm NaBiO3•2H2O/NaBiO3•xH2O heterostructures (30 °C) is enhanced about 8.8 times after ethanol treatment. The results suggest that the possible excited state corrsponding to 3.1 eV (400 nm) above the conduction band bottom is better matching conduction band of NaBiO3•2H2O than that corresponding to 3.3 eV (375 nm). The intermediate band within band gap corresponding to 2.6 eV (470 nm) due to ethanol treatment inducing surface defects contributes to the enhanced SPV. The investigation suggests that the SPV measurement is a helpful tool to investigate the fine structures of conduction and intermediate bands of NaBiO3•2H2O/NaBiO3•xH2O heterostructures and related photovoltaic and catalytic materials.