  Photo-gated transistors based on dye-sensitized nanocrystalline titanium
dioxide thin film are established. A transistor-like transport behavior
characterized by the linear increase, saturated plateau, and breakdown-like
increase in the voltage-current curve is achievable with a low driven bias for
the present device. The response current exhibits a linear dependence on the
intensity of gated light, and the measured maximum photosensitivity is
approximately 0.1 A/W. The dynamic responses for various light frequencies and
their dependences on the load resistances are investigated as well. The cut-off
frequency of ~50 Hz is abstracted, indicating the potential application for
economical and efficient light switch or optical communication unit. The dc
photo-gated response is explained by the energy level diagram, and is
numerically simulated by an equivalent circuit model, suggesting a clear
correlation between photovoltaic and photoconductive behaviors as well as their
optical responses.
