Key Sputtering Parameters for Precursor In₂O₃ Films to Achieve High Carrier Mobility

Owing to their extremely high carrier mobility (μ) of >100 cm²/(V s) and suitable low carrier concentrations, transparent conducting films of solid-phase crystallized H-doped In₂O₃ (spc-IO:H) exhibit high conductivity with high optical transparency over a broad frequency range. These properties can be attributed to solid-phase crystallization of the amorphous precursor film. Therefore, the development of high-quality spc-IO:H films requires the deposition conditions of the precursor films to be optimized. This study systematically investigates the effects of three key sputtering parameters, namely, water vapor partial pressure (P_H2O), radio frequency magnetron sputtering power (P_RF), and flow ratio of O₂ to total sputter gas (fO₂) on the crystallographic texture evolution of spc-IO:H films during solid-phase crystallization. In addition, the carrier transport in the resulting films is examined. P_H2O, P_RF, and fO₂ are found to be indispensable for producing high-mobility (>100 cm²/(V s)) spc-IO:H films. Furthermore, it is found that introducing a small amount of P_H2O during deposition, a lower P_RF, and a suitable fO₂ facilitates the formation of precursor films having a lower crystallite density. Moreover, after annealing at a temperature of 200 °C, the IO:H precursor films with a lower crystallite density are found to have larger crystal grains. However, the μ values of the postannealed IO:H films are mainly correlated with the stoichiometric deviation.