Fig. 6
Characteristics of WO3/GR after photo-induced modulation doping. a, b Current route and charge distribution in the WO3/GR device in case of UV light. Positive charges accumulate in WO3 under light illumination. Yellow, Cr/ Au; green, WO3; red, graphene; blue, SiO2; gray, Si. c Equivalent circuit model of the WO3/GR device. d Schematics of the band structure of the WO3/GR heterostructure and illustration of the photodoping mechanism, in which optical excitation first excites electrons from defects in WO3. Red (blue) lines represent the conduction (valence) band. The excited electrons enter the graphene, and the positively charged defects lead to modulation doping in the graphene