Modeling of amorphous InGaZnO4 thin film transistors and their subgap density of states

We report a model of the carrier transport and the subgap density of states in amorphous $\mathrm{In}\mathrm{Ga}\mathrm{Zn}{\mathrm{O}}_4$ ($a$ -IGZO) for device simulation of $a$ -IGZO thin-film transistors (TFTs) operated in both the depletion mode and the enhancement mode. A simple model using a constant mobility and two-step subgap density of states reproduced well the characteristics of the $a$ -IGZO TFTs. $a$ -IGZO exhibits low densities of tail states and deep gap states, leading to small subthreshold swings and high mobilities.