Facet-driven carrier separation in silicon quantum rods: a model for anisotropic nanocrystals

Abstract A precise understanding of surface effects is essential for interpreting the optoelectronic response of semiconductor nanostructures with complex geometries and reduced dimensions. In this work, we present a detailed atomistic analysis of the electronic structure of quantum rods (QR) with controlled facet transitions. Specifically, we study silicon QRs aligned along the (100) direction, featuring a gradual transition from (110) to (100) surface facet. We reveal how the resulting anisotropy drives spatial separation of charge carriers and modifies absorption characteristics. Our results show that shallow conduction and valence states tend to localize in different regions, resembling a type-II heterostructure. Despite changes in the size and the number of atoms, the energy gap of these anisotropic QRs remains around 2.0 eV. In contrast, the energy gap ranges from 2.0 to 3.0 eV for symmetric structures of comparable size. Our findings demonstrate that facet-engineered geometries can tune optical absorption thresholds and carrier separation in comparison to symmetric QRs.