Hydrogen-Doping-Enabled Boosting of the Carrier Mobility and Stability in Amorphous IGZTO Transistors

This study investigated the effect of hydrogen (H) on the performance of amorphous In-Ga-Zn-Sn oxide (a-In_0.29Ga_0.35Zn_0.11Sn_0.25O) thin-film transistors (TFTs). Ample H in plasma-enhanced atomic layer deposition (PEALD)-derived SiO₂ can diffuse into the underlying a-IGZTO film during the postdeposition annealing (PDA) process, which affects the electrical properties of the resulting TFTs due to its donor behavior in the a-IGZTO. The a-In_0.29Ga_0.35Zn_0.11Sn_0.25O TFTs at the PDA temperature of 400 °C exhibited a remarkably higher field-effect mobility (μ_FE) of 85.9 cm²/Vs, a subthreshold gate swing (SS) of 0.33 V/decade, a threshold voltage (V_TH) of -0.49 V, and an I_ON/OFF ratio of ∼10⁸; these values are superior compared to those of unpassivated a-In_0.29Ga_0.35Zn_0.11Sn_0.25O TFTs (μ_FE = 23.3 cm²/Vs, SS = 0.36 V/decade, and V_TH = -3.33 V). In addition, the passivated a-In_0.29Ga_0.35Zn_0.11Sn_0.25O TFTs had good stability against the external gate bias duration. This performance change can be attributed to the substitutional H doping into oxygen sites (H_O) leading to a boost in n_e and μ_FE. In contrast, the beneficial H_O effect was barely observed for amorphous indium gallium zinc oxide (a-IGZO) TFTs, suggesting that the hydrogen-doping-enabled boosting of a-IGZTO TFTs is strongly related to the existence of Sn cations. Electronic calculations of V_O and H_O using density functional theory (DFT) were performed to explain this disparity. The introduction of SnO₂ in a-IGZO is predicted to cause a conversion from shallow V_O to deep V_O due to the lower formation energy of deep V_O, which is effectively created around Sn cations. The formation of H_O by H doping in the IGZTO facilitates the efficient connection of atomic states forming the conduction band more smoothly. This reduces the effective mass and enhances the carrier mobility.