Capacitance-voltage characterization of polyfluorene-based metal-insulator-semiconductor diodes

Metal-insulator-semiconductor structures with conjugated polymer ethyl-hexyl substituted polyfluorene (PF2̱6) as the active semiconductor layer, Al2O3 as the insulating oxide layer, and p+-Si as the metal layer have been characterized by means of capacitance-voltage (C-V) and conductance-voltage methods. The negative shift of the flat-band voltage with increasing frequency arises from positive interface charges in the PF2̱6∕Al2O3 layer. From C-V measurements the unintentional doping density is evaluated as ∼5.7×1017cm−3 at frequencies above 20kHz. The interface trap density is estimated as ∼7.7×1011eV−1cm−2 at the flat-band voltage.