Highly insulating phase of Bi₂O₂Se thin films with high electronic performance

Bi₂O₂Se is highly competitive as a candidate of next-generation high-performance semiconductors. Though dubbed as semiconductor, Bi₂O₂Se films exhibited high conductance, i.e., metallic behavior, due to spontaneously ionized defects. Semiconducting/insulating films are of practical importance in broad applications based on low-power, high-performance electronics, the existence of which lacks firm evidence. Here, we synthesized highly insulating films in a controlled way, which exhibit semiconducting behavior with channel resistance up to 1 TΩ. The electron chemical potential lies within the band gap, in some cases, even below the charge neutrality level, signifying the trace of hole-type semiconducting. The performance of insulating devices remains high, comparable to high-quality devices previously. Especially, the threshold voltage (V_th) is positive, contrary to common negative values reported. Calculations indicate that our synthesis conditions suppress electron donors (Se vacancies (V_Se)) and promote the formation of compensating acceptors (Bi vacancies (V_Bi)), leading to insulating behaviors. Our work offers insights into electron dynamics of Bi₂O₂Se, moves one step further towards p-type transistors and provides a valuable playground for engineering ferroelectricity in high-performance semiconductors.