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

In this study, we examine the effect of oxygen vacancies (
${V}_{O}$
) 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 (Al
₂
O
₃
) growth using plasma-enhanced atomic layer deposition (PEALD). During the initial period of Al
₂
O
₃
deposition, trimethylaluminum precursors absorbed oxygen from the SnO layer and created the
${V}_{O}$
, which can form a
${V}_{O}$
-rich region at the Al
₂
O
₃
/SnO interface. By modulating the oxygen plasma density during the PEALD process, the
${V}_{O}$
was effectively controlled, allowing the electrical characteristics to transition from ambipolar behavior to
${p}$
-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.