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 Cfree by free electron charges can be separated from C
_loc
by localized trap charges through the proposed method.