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In order to model dc characteristics of n-channel amorphous InGaZnO thin-film transistors from experimentally obtained density of states (DOS), the acceptorlike DOS is extracted from the optical response of capacitance-voltage characteristics and confirmed by the technology computer-aided design (TCAD) simulation comparing with the measured data. Extracted DOS is a linear superposition of two exponential functions (tail and deep states), and its incorporation into TCAD model reproduces well the experimental current-voltage characteristics over the wide range of the gate and drain voltages. The discrepancy at higher gate voltage is expected to be improved by incorporating a gate voltage-dependent mobility in the model.

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 computeraided 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.Index Terms-Amorphous, density of states (DOS), indiumgallium-zinc-oxide (InGaZnO), multifrequency capacitancevoltage (C-V ) characteristics, technology computer-aided design (TCAD), thin-film transistors (TFTs).

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