Trap densities in amorphous-InGaZnO4 thin-film transistors

Trap densities in amorphous-InGaZnO4 (α-IGZO) 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 1.7×1016cm−3eV−1 in the deep energy far from the conduction band edge (Ec), but become larger near Ec. Moreover, postannealing reduces the trap density near Ec, which is associated with the reduction of the hysteresis in the current-voltage characteristics. The annealed α-IGZO does not have a Gaussian-type state and has fewer tail states than amorphous Si.