Extraction of Subgap Density of States in Amorphous InGaZnO Thin-Film Transistors by Using Multifrequency Capacitance–Voltage Characteristics

An extraction technique for subgap density of states (DOS) in an n-channel amorphous InGaZnO thin-film transistor (TFT) by using multifrequency capacitance-voltage (
C
-
V
) characteristics is proposed and verified by comparing the measured
I
-
V
characteristics with the technology computer-aided design simulation results incorporating the extracted DOS as parameters. It takes on the superposition of exponential tail states and exponential deep states with characteristic parameters for
N

_TA
= 1.1 × 10
¹⁷
cm
^-3
· eV
^-1
,
N

_DA
= 4 × 10
¹⁵
cm
^-3
· eV
^-1
,
kT

_TA
= 0.09 eV, and
kT

_DA
= 0.4 eV. The proposed technique allows obtaining the frequency-independent
C
-
V
curve, which is very useful for oxide semiconductor TFT modeling and characterization, and considers the nonlinear relation between the energy level of DOS and the gate voltage
V

_GS
. In addition, it is a simple, fast, and accurate extraction method for DOS in amorphous InGaZnO TFTs without optical illumination, temperature dependence, and numerical iteration.