Figure 6. Photo-response of Gr/TiO₂ heterostructure at zero gate voltage.

(a) I_sd vs. V_sd output characteristics in the dark (red color plot) and under visible light illumination (blue color plot). (A) white LED (P_o = 36 mW) was used to illuminate the device. (b) The comparison of transfer characteristics (I_sd vs V_g) in the dark (red color plot) and under illumination (blue color plot) at V_sd = 0.2 V. In the dark, the Gr/TiO₂ heterostructure showed typical graphene ambipolar transfer characteristics. Under illumination, a linear transfer characteristic is exhibited, (c) Output characteristic of Gr/TiO₂ heterostructure under illumination at different gate bias voltages from −20 V to 20 V with 5 V steps. (d) The on/off temporal response of Gr/TiO₂ heterostructures at zero gate bias. V_sd = 0.2 V was applied during measurement. Insert: the zoomed plot showing fast photo-response behavior.