Composition-dependent structural and electrical properties of p-type SnOx thin films prepared by reactive DC magnetron sputtering: effects of oxygen pressure and heat treatment

Abstract

The composition-dependent structural and electrical properties of SnO_x films prepared by means of reactive DC sputtering at various oxygen partial pressures (P_O) and post-heat treatment temperatures (T_A) were investigated, toward these films' potential use in p-channel oxide thin-film transistors (TFTs). A SnO_x film fabricated under the lowest studied P_O of 4% and heat-treated at 210 °C consisted of dendritic phases and irregular protrusions of metallic Sn. The resulting p-channel SnO_x thin-film transistors suffered from marginal field effect mobility (μ_FE) and low on/off current ratio (I_ON/OFF), suggesting that the imperfect phases caused by oxygen-deficient stoichiometry hinder hole carrier conduction and act as bulk trap states. The heterogeneous structures observed in SnO_x films annealed at 210 °C could be eliminated by increasing P_O during fabrication. The resulting TFTs based on p-type SnO_x films prepared at the high P_O of 8% showed high mobilities up to 2.8 cm² V⁻¹ s⁻¹ and reasonable I_ON/OFF of approximately 10³, demonstrating the critical role of these films' homogeneous ordered aggregates without any imperfect phases such as a dendritic phase or irregular protrusions of metallic Sn. Among TFTs based on the films fabricated under 8% P_O, the μ_FE and I_ON/OFF performance metrics degraded with increasing T_A from 210 to 300 °C, which was mainly related to the 2SnO → SnO₂ + Sn disproportionation reaction.