Abstract
Selective area growth (SAG) of III-V nanowires (NWs) by molecular beam epitaxy (MBE) and related epitaxy techniques offer several advantages over growth on unpatterned substrates. Here, an analytic model for the total flux of group III atoms impinging NWs is presented, which accounts for specular re-emission from the mask surface and the shadowing effect in the absence of surface diffusion from the substrate. An expression is given for the shadowing length of NWs corresponding to the full shadowing of the mask. Axial and radial NW growths are considered in different stages, including the stage of purely axial growth, intermediate stage with radial growth, and asymptotic stage, where the NWs receive the maximum flux determined by the array pitch. The model provides good fits with the data obtained for different vapor–liquid–solid and catalyst-free III-V NWs.
Highlights
Flux influenced by specular re-emission and shadowing. This allows one to determine the shadowing length of NWs corresponding to the full shadowing of the substrate surface in molecular beam epitaxy (MBE)
A full description of MBE growth of III-V NWs on reflecting substrates that accounts for all possible factors, influencing the growth process and NW morphology, is beyond reach to this end
This late stage of NW growth occurs for S ≥ P2, where the substrate surface is entirely shadowed by the NW array and is exactly identical for MBE growth of NWs on any substrate
Summary
A high aspect ratio (length over radius) is crucial for the applications and fundamental physical properties of NWs, such as onedimensional transport of charge carriers, directional light emission, crystal purity within axial or radial heterostructures, abruptness of heterointerfaces, and crystal phase switching in III-V NWs [10] These features explain the importance of controlling the NW dimensions during growth. I try to fill the gap by developing an analytic model for the total group III flux influenced by specular re-emission and shadowing. This allows one to determine the shadowing length of NWs corresponding to the full shadowing of the substrate surface in MBE. The model is quite general and should work well for metal-catalyzed and catalyst-free NWs in different material systems, where MBE SAG is performed on a masked substrate
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