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 × 10¹⁸ cm^-3 · eV_-1, N_DA = 2.8 × 10¹⁷ cm^-3 · eV-1, kT_TA = 0.04 eV, and kT_DA = 0.77 eV). We note that the gate-bias-dependent Cfree by free electron charges can be separated from C_loc by localized trap charges through the proposed method.