A review on vapor-solid growth of GaAs-based nanowires by molecular beam epitaxy: insights from twins, facets, dopants, and dilute species.

Vapor-solid (VS) growth presents a robust alternative to vapor-liquid-solid (VLS) techniques for the fabrication of nanowires (NWs), particularly in applications involving doping, accurate control of composition and heterointerfaces and formation of high-uniformity NW arrays. Despite many obvious advantages, surprisingly few efforts have been undertaken to establish VS growth of GaAs-based NWs, especially in molecular beam epitaxy (MBE) growth. This review encompasses recent developments and breakthroughs in catalyst-free VS growth of GaAs-based NWs through selective-area MBE. It emphasizes the significance of template design on NW characteristics and examines the important roles of twin defects, growth facets, dopants and dilute group-V species, such as silicon (Si) and antimony (Sb) on growth dynamics, adatom diffusion, and crystal phase purity. Si doping emerges as a critical factor in stabilizing twin defects, improving axial growth, NW uniformity, and n-type conduction in GaAs NWs otherwise not feasible in VLS-type growth. The inclusion of dilute Sb in these nanostructures further promotes surfactant action while reducing twin defects, resulting in high-aspect-ratio NWs with superior structural and optical properties. These findings are supported by microscopic growth models that illustrate the relevance of twin defects and competing growth facets. The selective-area MBE growth is further applied to VS-grown ternary AlGaAs NWs as well as axial AlGaAs/GaAs(Sb) and InGaAs/GaAs(Sb) NW heterostructures and their growth-structure-property relationships are elucidated by correlated high-resolution electron microscopy and micro-photoluminescence spectroscopy. This review therefore underscores VS growth of GaAs-based NWs under MBE processes as a versatile approach for the precise engineering of NW heterostructures and implementation on Si substrates.