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.