Dopant-induced indirect-direct transition and semiconductor-semimetal transition of bilayer SnSe.

Tin selenide (SnSe) is a layered semiconductor, which is reported to be the best thermoelectric material to date. Few-layer tin selenide is highly sensitive to external conditions such as strain, pressure, or temperature. Crystal structure of SnSe is orthorhombic, where atoms are arranged in an accordionlike structure with nonbonding intralayer interactions. Bulk and few-layer pristine SnSe are reported to have indirect electron bandgaps. Based on the results from first-principles density functional theory calculations, we show that two major structural changes can happen upon substitutional chemical doping of bilayer SnSe. Substitutional chemical doping can manipulate the directionality of interlayer interactions of bilayer SnSe, which results in an indirect-direct transition of the electronic bandgap. Our results also suggest that larger dopant atoms can convert the nonbonding intralayer interactions to covalent bonding. Such an increase in the atomic orbital overlap may result in a semiconductor-semimetal transition. [ABSTRACT FROM AUTHOR]