Fully Transfer Characteristic-Based Technique for Surface Potential and Subgap Density of States in p-Channel Polymer-Based TFTs

We report a fully subthreshold current-based technique for characterization of subgap density of states [DOS:g(E)] with consistent mapping of the surface potential (ψ_S) in p-channel polymer-based thin-film transistors (PTFTS). Initially, we propose a technique for extraction of the DOS over the bandgap using the gate voltage (V_GS)-dependent ideality factor [m(V_GS)] from the transfer characteristics of the PTFTs under subthreshold operation. We also propose a technique for a consistent nonlinear mapping of V_GS to the subgap energy level by converting m(V_GS) to ψ_S. Through combining the two methods, the exponential tail and deep g(E) are obtained to be N_TD=1·1×10¹⁷ [eV^-1·cm^-3], kT_TD=0·035 [eV], N_DD=9·8×10¹⁶ [eV^-1·cm^-3], and kT_DD=0·80 [eV] over the bandgap.