Direct and alternating electrical performance of TiO2/SiO2/p-Si heterojunction under visible illumination

The titanium dioxide (TiO2) thin film was deposited on the surface of p-type silicon (Si) substrate using spray pyrolysis technique and TiO2/SiO2/p-Si heterojunction was formed. The microstructure of the heterojunction surface is characterized by X-ray diffraction and atomic force microscopy. The energy-band gap (similar to 3.38 eV) and the work function (similar to 5.53 eV) of the TiO2 thin film were calculated by ultraviolet-visible spectrum and ultraviolet photoelectron spectroscopy, respectively. The energy-band structure of the heterojunction is established. The current-voltage characteristics of the heterojunction is investigated, which displays a typical diode rectifying property. The alternating current capacitance and impedance are measured under different visible light intensities, and the heterojunction exhibits good photosensing performance. The resistance and impedance of the heterojunction decrease with increasing of light intensity, while the capacitance value increases. The phenomenon is mainly attributed to the decrease of Fermi level difference between TiO2 thin film and Si with the increase of light intensities, which can be explained by the energy-band diagram of the TiO2/SiO2/Si heterojunction.