The influence of oxygen partial pressure on the performance and stability of Ge-doped InGaO thin film transistors

The device performance and bias stability of radio frequency (RF) sputtered Ge-doped InGaO (GIGO) thin film transistors (TFTs) were investigated as a function of oxygen partial pressure during the deposition step. At low oxygen partial pressure, the electrical performance and stability of GIGO TFTs were significantly improved with a decrease of oxygen deficient bonding states, suggesting strong oxygen bonding ability of Ge atoms. We demonstrate that these changes can be corroborated with the evolution of the electronic structure, such as band alignment and band edge states below the conduction band, as measured by X-ray photoelectron spectroscopy and spectroscopic ellipsometry analysis. As the oxygen partial pressure decreased, the energy difference between the conduction band minimum and Fermi level and the deep band edge states was decreased. In particular, it was revealed that, with an increase of oxygen partial pressure, the relative energy level of the band edge states was shifted to a deeper level within the bandgap.