A self-assembling method to align metal nanoparticles to quantum dots

Abstract

Hybrid nanostructures are known to elicit an enhanced optical response due to plasmonic coupling effects. A relevant material system of current interest is InAs-ErAs composite structure where semi-metallic ErAs nanoparticles (NPs) are coupled to InAs quantum dots (QDs). In order to achieve well-defined coupling, a precise alignment must occur between the QD and metal NP. However, the low migration of Er on III-V surfaces (due to strong bond strength) combined with random nucleation of QDs prevents accurate placement. Here we report a novel way to potentially address both these issues, where direct assembly of ErAs metal NPs over InAs QDs is achieved with molecular beam epitaxy (MBE). Using the strain driven nucleation mechanism we show that lightly Er doped InAs QDs can be self-aligned to underlying InAs QDs. Annealing uncapped Er:InAs QDs at high temperature desorbs the In atoms in QD. However, due to much lower volatility and limited solubility, Er atoms condense out and nucleate as ErAs NPs that align with the underlying InAs QDs. This method can potentially position other low-mobility materials (in our case ErAs) amenable to directed assembly processes of a higher mobility component (in this case InAs). To be successful the higher mobility/volatility component must be capable of dissolving the low mobility/volatility component without significantly changing its directed assembly process.