Oxygen Stoichiometry Engineering in Bi2O2Se for Carrier Regulation and High-Performance Homojunction Photodetectors.

While lattice matching facilitates the construction of two-dimensional (2D) homojunctions by alleviating interface compatibility issues, realizing effective carrier polarity modulation within a single material system remains a significant challenge. In this work, we developed a versatile carrier regulation strategy for 2D Bi2O2Se by modulating oxygen content in the form of oxygen deficiency or oxygen adsorption. Specifically, n-type conduction is achieved by introducing SiO2 powder into the growth precursor Bi2O3 to suppress oxygen sublimation, thereby inducing oxygen vacancies during CVD growth of Bi2O2Se. Conversely, by treating intrinsic Bi2O2Se with ultraviolet ozone (UVO), surface oxygen adsorbates function as electron trap centers to deplete electron carriers inside the underneath layer, achieving a hole-dominated transport channel. These distinct mechanisms are substantiated by comprehensive material characterization and electrical measurements. Leveraging this carrier polarity modulation, vertical Bi2O2Se homojunctions were fabricated. The resulting device exhibits exceptional performance, featuring an ultralow dark current of 710 fA, a photoresponsivity of 3.61 A/W, and a noise equivalent power on the scale of fW/Hz1/2.