Figure 3.

Schematic band diagram for the standby condition in air (a) in the dark and (b) under the UV light. The Fermi energy in the dark (E_F) splits to the quasi Fermi energies for the electron and hole (E_Fn and E_Fp) under the UV light. The carrier excitation processes due to light irradiation are shown by ① and ② as explained in the text. Both the electron and hole transitions are shown in the ② process. The band diagrams under NO exposure are shown (c) in the dark and (d) under the UV light. The relative variations of the adsorbed O₂⁻ and NO⁻ charges are drawn. The variations in the depletion region depths in the dark and under the light before and after exposure to NO are also shown.