Understanding the anisotropic growth of vapor–solid grown Pb <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> </mml

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.