The role of interstitial native defects in the topological insulator Bi2Se3

Bi2Se3 is a prominent narrow gap semiconductor with a rhombohedral crystal structure and potential applications in thermoelectric and spintronic technologies. Its electrical conduction is ruled by native point defects inducing an n-type degenerate behavior. Here, we present a first principles study of the point defects in Bi2Se3, focusing on the relevance of the interstitial sites. A density functional methodology was employed with van der Waals correction and spin-orbit coupling in order to achieve a better description of the defects. The results indicate that interstitial Bi atoms in octahedral sites between two consecutive quintuple layers have a lower formation energy than selenium vacancies and that these interstitials could act as a possible source of free electron carriers. In addition, we show that the utilization of an experimental or strained lattice constant in the calculations may lead to an under- or overestimation of the defect formation energies.