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 0.29 Ga 0.35 Zn 0.11 Sn 0.25 O) thin-film transistors (TFTs). Ample H in plasma-enhanced atomic layer deposition (PEALD)-derived SiO 2 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 0.29 Ga 0.35 Zn 0.11 Sn 0.25 O TFTs at the PDA temperature of 400 °C exhibited a remarkably higher field-effect mobility (μ FE ) of 85.9 cm 2 /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 ∼10 8 ; these values are superior compared to those of unpassivated a -In 0.29 Ga 0.35 Zn 0.11 Sn 0.25 O TFTs (μ FE = 23.3 cm 2 /Vs, SS = 0.36 V/decade, and V TH = -3.33 V). In addition, the passivated a -In 0.29 Ga 0.35 Zn 0.11 Sn 0.25 O 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 SnO 2 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.