Origin of Ambipolar Behavior in p-Type Tin Monoxide Semiconductors: Impact of Oxygen Vacancy Defects

Abstract

In this study, we examine the effect of oxygen vacancies (<inline-formula> <tex-math notation= LaTeX >${V}_{O}$ </tex-math></inline-formula>) near the back surface of p-type tin monoxide (SnO) semiconductors on the device performance of its thin-film transistors (TFTs). Non-stoichiometry of the SnO surface layer was controlled through oxidant exposure conditions during alumina (Al₂O₃) growth using plasma-enhanced atomic layer deposition (PEALD). During the initial period of Al₂O₃ deposition, trimethylaluminum precursors absorbed oxygen from the SnO layer and created the <inline-formula> <tex-math notation= LaTeX >${V}_{O}$ </tex-math></inline-formula>, which can form a <inline-formula> <tex-math notation= LaTeX >${V}_{O}$ </tex-math></inline-formula>-rich region at the Al₂O₃/SnO interface. By modulating the oxygen plasma density during the PEALD process, the <inline-formula> <tex-math notation= LaTeX >${V}_{O}$ </tex-math></inline-formula> was effectively controlled, allowing the electrical characteristics to transition from ambipolar behavior to <inline-formula> <tex-math notation= LaTeX >${p}$ </tex-math></inline-formula>-channel only conduction. This study demonstrates the importance of the back surface of SnO, suggesting a new perspective of ambipolar behavior in p-type SnO semiconductors.