Engineering coexistence between free and trapped carriers via extrinsic polarons
The transition between delocalized and localized electronic configurations is a characteristic property of all small-polaron systems. In this study, we explore a doping approach by which the coexistence between delocalized and localized electronic states may be precisely tuned within extrinsic polaron systems. Through comprehensive ab initio calculations employing hybrid functionals, for which Ti-doped SnO2 is selected as a model system, it is demonstrated how strain and alloying can be utilized to achieve a high degree of control over the activation energetics separating localized and delocalized electronic states. By means of a phenomenological tight-binding analysis of our ab initio results, it is shown that two physical parameters play a dominant role in the associated transition physics: (1) the dopant electronic offset Δa, and (2) the dopant bandwidth W. Overall, this study presents an exciting route toward tailoring the coexistence between delocalized and localized states with a potentially much greater degree of control than is currently possible in intrinsic materials.
