Extraction of bulk and interface trap densities in amorphous InGaZnO thin-film transistors

Abstract

The authors determine the density of interface and bulk trap states in the amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) by using a simple extraction method. To determine the bulk trap density, the current–voltage curve is measured between the source and drain electrodes of the TFT at room temperature under the flat-band condition. In the high voltage region, the carrier transport is well described by the space charge limited current controlled by the bulk trap states that are exponentially distributed in energy with a trap density at the conduction band edge of 6.27 × 1017 cm−3 eV−1 and an inverse slope for the trap distribution of 0.12 eV. The density of traps at the a-IGZO/gate dielectric interface is calculated by subtracting the bulk trap components from the density of total subgap trap states extracted from the subthreshold slope in the transfer curve and the frequency-independent capacitance-voltage characteristics. The experimental results show that the contribution of the interface trap is more significant compared to that of the bulk trap in the subgap density of states of the fabricated a-IGZO TFTs.