Experimental observation of the density of localized trapping levels in organic semiconductors

We have approximated the tail of the Gaussian distribution of states of organic semiconductors with an exponential function. We have used this approach to calculate the carrier concentration in organic materials, and subsequently the charge distribution in the accumulation region of a field effect device, the effective width of an accumulation layer (Debye length), and the space-charge capacitance in accumulation mode. Small signal high frequency capacitance-ramp voltage measurements performed at various temperatures show good agreement with this model and the characteristic temperature of the exponential function has been estimated from these measurements based on the theory developed.