Trap densities in amorphous-InGaZnO4 thin-film transistors

Abstract

Trap densities in amorphous-$\mathrm{In}\mathrm{Ga}\mathrm{Zn}{\mathrm{O}}_4$ $\left(\alpha \text{-}\mathrm{IGZO}\right)$ are extracted directly from the capacitance-voltage characteristics of thin-film transistors at low frequencies. It is found that the trap densities are flat in the energy gap, and are $1.7\times {10}^{16}{\mathrm{cm}}^{-3}{\mathrm{eV}}^{-1}$ in the deep energy far from the conduction band edge $\left(E_c\right)$ , but become larger near $E_c$ . Moreover, postannealing reduces the trap density near $E_c$ , which is associated with the reduction of the hysteresis in the current-voltage characteristics. The annealed $\alpha \text{-}\mathrm{IGZO}$ does not have a Gaussian-type state and has fewer tail states than amorphous Si.