Fig. 3: Illustration and theory of the photocurrent generation.
a and b Illustration of the thermal mechanism of the photocurrent generation when the top graphene layer is biased slightly (a) below or (b) above the impurity level (which corresponds to i1b, i2b-curves on Fig. 1d). c Illustration of the photocurrent generation at zero bias at 2 gate voltages near impurity alignment. d Theoretically calculated photocurrent and e \({d}^{2}{I}_{{{{\rm{b}}}}}/d{V}_{{{{\rm{b}}}}}^{2}\) map as a function of gate and bias voltages, well reproducing experimental results. f and g Slices of maps d and e at three different bias voltages: f Vb = 0.25 V; g Vb = 5 mV, along dashed line on (d); h Vb = 0. The red dashed and dotted lines on g, h demonstrate the contribution of the top and bottom layers, respectively, to the total photocurrent. The heating of the layers is assumed to be slightly different, δTt = 1.2δTb, which gives a non-zero photocurrent at Vb = 0.
