Heavy Doping-Induced Phase Segregation and Heterojunction Formation

Elucidating the atomic arrangement of dopant states at high doping concentrations is crucial for understanding structure-property relationships in materials. On the atomic scale, closely connected interfaces, particularly coherent interfaces, can effectively suppress interface-induced trapping processes. Although not yet experimentally verified, heavy doping holds promise for generating heterojunctions within host materials. This study combines spherical aberration-corrected electron microscopy and first-principles calculations to reveal that, at low doping concentrations (1%), Bi primarily occupies W sites, resulting in substitutional doping. However, at high doping concentrations (>10%), we have identified the formation of a Β-Bi₂O₃ phase within the WO₃ host. The formation of these heterojunctions can effectively facilitate electron transfer due to favorable band alignment and potential energy differences between Bi₂O₃ and WO₃. The findings of this study are crucial for rethinking the atomic structures of dopant states at high doping concentrations and their potential application in the development of heterojunctions.