The origin of evolutionary device performance for GeGaInOx thin film transistor as a function of process pressure

This paper addresses changes in device performance for GeGaInOx (GGIO) thin film transistors deposited as a function of process pressures, and the mechanisms responsible for electronic band structure and defect states within sub-gap states. As the process pressure decreased from 5 to 1 mTorr during sputtering of the GGIO active layer, the saturation mobility increased from 6.51 to 11.18 cm²/Vs and the sub-threshold swing value decreased from 0.64 to 0.21 V/decade. Conduction band areas measured by x-ray absorption spectroscopy in GGIO films increased as the total process pressure decreased from 5 to 1 mTorr, which can help charge transport in GGIO semiconductors. In addition, the ΔVth shift during positive bias temperature stability for 3 h was also enhanced from 17.5 to 6.2 V. This improvement can be attributed to the reduction of relative near conduction band edge defect states, which was found in not only at the GGIO films level by spectral ellipsometry, but also at the device level by the Meyer-Neldel rule.