Understanding the anisotropic growth of vapor-solid grown Pb1-xSn_xTe nanowires

Pb_0.5Sn_0.5Te is a topological crystalline insulator, which holds promise for scattering-free transport channels and fault-tolerant quantum computing. As the topologically non-trivial states live on the surface, the nanowire (NW) geometry, with a high surface-to-volume ratio, is ideal for probing these states. The controlled growth of Pb_0.5Sn_0.5Te NWs using molecular beam epitaxy has been shown before, but an understanding of the anisotropic growth and the resulting morphology is lacking. Here, based on experimental observations, we develop a model that describes the evolution of NW morphology as a function of growth time. It is found that the anisotropic morphology can be described by a combination of direct impingement, mask diffusion and facet diffusion which results in a transition from a Te-limited growth regime to a group IV-limited growth regime. This growth model allows us to design more targeted experiments which could lead to a higher flexibility in device design.