Simulator was calibrated with a reference photodiode. An HP
4284A LCR-meter operated in the frequency range 20–106 Hz
(vac = 20 mV ac voltage) was used to measure in the dark the
complex admittance Y(v), from which the capacitance C(v) = ImY
(v)/v and the conductance G(v) = ReY(v) were extracted. We have
carefully analyzed the low frequency regime in order to make sure
that the extracted C(v) and G(v) are not influenced by any parasitic
circuit reactance [28].