Tailoring Nanoscale Crystal Polytype Selection for Quantum Confinement Engineering

Electrically-controlled and integrable single photon sources are essential components of quantum information systems. Although semiconductor quantum dots (QDs), including InGaN/GaN QDs-in-nanowires, are promising for room temperature applications, their scalability is limited by alloy composition fluctuations. Here, we aim to create alloy-fluctuation-free QD arrays, namely poly-type QDs-in-NWs, using self-catalyzed NW growth at vapor-liquid-solid (VLS) triple-junctions. We demonstrate, for the first time, epitaxy of GaN NW ensembles and films with a significant ZB content on Si(001). In addition to presenting our novel two-step molecular-beam epitaxy (TS-MBE) approach to control SixNy layer formation and subsequent GaN phase selection, we reveal new insight into the relative roles of surface and step-edge diffusion on film to nanowire transitions. The NWs exhibit remarkable photoluminescence (PL) characteristics consisting of distinct emission from donor-acceptor pairs (DAP) and excitonic transitions related to both ZB and WZ GaN. This first demonstration of epitaxial growth and PL emission from ZB GaN NWs on Si(001) provides a crucial step toward the realization of GaN QDs-in-NWs for single photon emitters.