Modified Conductance Method for Extraction of Subgap Density of States in a-IGZO Thin-Film Transistors

We propose a modified conductance method for extraction of the subgap density of states (DOS) in amorphous indium-gallium-zinc oxide thin-film transistors by using the measured capacitance and conductance through the capacitance-voltage (C-V) measurement. In the proposed method, the subgap DOS [gA(E)] is extracted from the frequency-dispersive C-V characteristics by localized traps in the active channel region. The extracted gA(E) shows a superposition of the exponential tail states and the exponential deep states over the bandgap (NTA= 3 × 1018cm-3· eV-1, NDA= 2.8 × 1017cm-3· eV-1, kTTA= 0.04 eV, and kTDA= 0.77 eV). We note that the gate-bias-dependent Cfree by free electron charges can be separated from Clocby localized trap charges through the proposed method.