Vapor-liquid-solid growth of germanium nanostructures on silicon

Abstract

The pressure and temperature dependencies for vapor-liquid-solid (VLS) growth of Ge nanostructures on Si using chemical vapor deposition are reported. Gold nanodots self-assembled by evaporation on clean hydrogen-terminated and heated Si substrates are used to seed the liquid eutectic VLS growth. Digermane pressures are varied from 4×10−5 to 1×10−2Torr and substrate temperatures from 400 to 600°C for heteroepitaxial growth on Si(111). Two types of nanostructures are identified, nanowires and nanopillars, with a transition from nanopillar growth to nanowire growth occurring with increasing pressure. Nanowires are characterized by rapid vertical growth, long-aspect-ratio structures, and linear dependence of the growth rate on pressure. At lower pressures a transition to nanopillars is observed; these exhibit both vertical and lateral growth with typical aspect ratios of 1:2. For Si(111) substrates nanowires grow epitaxially with their growth axis along the ⟨111⟩ direction. High-resolution transmission electron microscopy shows that the Ge nanowires are relaxed to their equilibrium lattice spacings a short distance from the Si substrate interface.

Growth of Ultralong ZnS/SiO2 Core−Shell Nanowires by Volume and Surface Diffusion VLS Process

“…In a much earlier work, Wagner and Ellis outlined for the Au-Si system what is generally regarded today as the classic vapor-liquid-solid (VLS) nanowire growth mechanism, in which a diffusing species is transmitted through the bulk of a metal catalyst in liquid phase before incorporating into the growing nanowire. 20 Such a process may be easily applied to other dual component systems, 21 which often, 22,23 but not always, 24 appear to mimic the Au-Si model system. Growth mechanisms in multiple component systems, however, have proved much more difficult to conclusively identify, as in many cases the final product is not well-explained by this VLS process.…”

Growth kinetics controlled rational synthesis of germanium nanotowers in chemical vapor deposition

“…2b) and the top of nanotower contains Au-riched Au-Ge alloy (Fig. 2c), confirming an Au-nanoparticle catalyzed growth process [21,22].…”

Synthesis of silicon and germanium nanowires.

“…Nanowire heterostructures require stringent control of growth parameters and their resulting electrical and optical properties are anticipated to enable valuable electronic, photonic, and sensing applications. 43 While many studies have investigated the final dimensions and orientations of semiconductor nanowires, 18,19 there have been few studies of nanowire synthesis during growth. 21 Such real time studies can greatly enhance the understanding of growth mechanisms and provide for the controlled fabrication of intricate heterostructured devices that otherwise may be difficult to achieve.…”

“…17,18 Although our initial investigations dealt exclusively with disilane and digermane precursor gases, the majority of other researchers utilize silane and germane for nanowire growth. Disilane is generally known to be more reactive than silane; 63 This greater reactivity of the dimolecular species versus the molecular species is consistent with our observation that disilane and digermane result in nanowire growth at lower pressures and temperatures than silane and germane, respectively.…”