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 [g(A)(E)] is extracted from the frequency-dispersive C-V characteristics by localized traps in the active channel region. The extracted g(A)(E) shows a superposition of the exponential tail states and the exponential deep states over the bandgap (N-TA = 3 x 10(18) cm(-3) . eV(-1), N-DA = 2.8 x 10(17) cm(-3) . eV(-1), kT(TA) = 0.04 eV, and kT(DA) = 0.77 eV). We note that the gate-bias-dependent C-free by free electron charges can be separated from C-loc by localized trap charges through the proposed method.