Giant tunable Rashba spin splitting in a two-dimensional BiSb monolayer and in BiSb/AlN heterostructures

The search for novel two-dimensional giant Rashba semiconductors is a crucial step in the development of the forthcoming nanospintronic technology. Using first-principles calculations, we study a stable two-dimensional crystal phase of BiSb having buckled honeycomb lattice geometry, which is yet unexplored. The phonon, room temperature molecular dynamics, and elastic constant calculations verify the dynamical and mechanical stability of the monolayer at 0 K and at room temperature. The calculated electronic band structure reveals the direct band gap semiconducting nature of a BiSb monolayer with the presence of a highly mobile two-dimensional electron gas (2DEG) near the Fermi level. Inclusion of spin-orbit coupling yields the giant Rashba spin-splitting of a 2DEG near the Fermi level. The calculated Rashba energy and Rashba splitting constant are 13 meV and 2.3 eV\AA{}, respectively, which are amongst the largest yet known Rashba spin splitting parameters in 2D materials. We demonstrate that the strength of the Rashba spin splitting can be significantly tuned by applying in-plane biaxial strain on the BiSb monolayer. The presence of the giant Rashba spin splitting together with the large electronic band gap (1.6 eV) makes this system of peculiar interest for optoelectronics applications. Furthermore, we study the electronic properties of BiSb/AlN heterostructures having a lattice mismatch of 1.3% at the interface. Our results suggest that a BiSb monolayer and BiSb/AlN heterostructure systems could be potentially used to develop highly efficient spin field-effect transistors, optoelectronics, and nanospintronic devices. Thus, this comprehensive study of two-dimensional BiSb systems can expand the range of possible applications in future spintronic technology.