Growth of BiSb on GaAs (001) and (111)A surfaces: A joint experimental and theoretical study

The integration of the Bi1−xSbx topological insulator on GaAs is studied both experimentally and theoretically on (001) and (111)A surfaces. The molecular beam epitaxy of thin Bi0.9Sb0.1 layer on both substrates leads to the observation of different growth modes: Volmer Weber for GaAs(001) and Stranski–Krastanov for GaAs (111)A. By first principles calculations, we corroborate these observations. On the (001) surface at the early stages of deposition, we show that Bi atoms diffuse more easily until they agglomerate to form isolated islands on the surface, favoring a 3D growth. Here, each island can have an independent growth direction. On contrary, the diffusion of Bi atoms on the (111)A surface is limited: it is favorable for Bi atoms to bond directly with GaAs, creating thus a wetting layer before a further Stranski–Krastanov growth.