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 × 10 ¹⁸ cm ^-3 ̇ eV ^-1, N _DA = 2.8 × 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.