Impact of hydrogen dopants incorporation on InGaZnO, ZnO and In2O3 thin film transistors

In this work, hydrogen (H) plasma treatment is implemented to dope the indium gallium zinc oxide (InGaZnO), zinc oxide (ZnO), indium oxide (In2O3) thin-film transistors (TFTs). We systematically analyze the active defect states inside these n-type metal oxides and reveal how they are impacted by the H dopants incorporation, combining the device transfer characteristics (including threshold voltage, subthreshold slope, carrier mobility), the X-ray photoelectron spectra, the numerical and theoretical investigations. An increase of the field-effect mobility of these TFTs is mainly attributed to the decreased interface and bulk tail-distributed traps, after an appropriate amount of the H dopants is incorporated. In ZnO, hydrogen exclusively acts as a shallow donor during the plasma treatment, while the zinc vacancy Zn(Vac) cannot be passivated by the H dopants as no improvement of the subthreshold slope (SS) is observed in the hydrogenated ZnO TFT. The H interstitial (Hi) incorporated into In2O3 is stable in the + charge state at equilibrium, then changes in the – charge state as the Fermi level energy EF gets closer to the bottom of conduction band. Due to the H insertion into an oxygen vacancy Vo, the VoH complex (acting as acceptor) is formed in InGaZnO with the increased H plasma treatment duration, leading to the degraded SS. This paper clarifies the H dopants’ role and the different dominant defects inside the three-type TFTs, which may benefit in systematic understanding and exploration of the H dopants incorporation into the InGaZnO, ZnO and In2O3 films for the TFTs improvement and optimization.