Nanoparticle stability in axial InAs-InP nanowire heterostructures with atomically sharp interfaces.
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The possibility to expand the range of material combinations in defect-free heterostructures is one of the main motivations for the great interest in semiconductor nanowires (NWs). However, most axial NW heterostructures suffer from interface compositional gradients and kink formation, as a consequence of nanoparticle (NP) NW interactions during the metal-assisted growth. Understanding such interactions and how they affect the growth mode is fundamental to achieve full control over the morphology and the properties of NW heterostructures for device applications. In this contribution we demonstrate that the sole parameter affecting the growth mode (straight or kinked) of InP segments on InAs NW stems by the Au-assisted vapour-liquid-solid (VLS) method is the NP composition. Tailoring the In/Au ratio of the NPs by the precursor fluxes at a fixed growth temperature enabled us to tune the NP contact angle and to find the conditions for achieving straight and radius-uniform InAs-InP NW heterostructures (single and double) with atomically sharp interfaces. We present a model that is capable of describing all the experimentally observed phenomena: straight growth versus kinking, the stationary NP compositions in pure InAs and InAs-InP NWs, the crystal phase trends, and the interfacial abruptness. Taking into account different NW/NP interfacial configurations (forming wetting or non-wetting monolayers in vertical or tapered geometry), our generalized model provides the conditions of NP stability and abrupt heterointerfaces for a rich variety of growth scenarios.