High efficiency ultraviolet emission from AlxGa1-xN core-shell nanowire heterostructures grown on Si (111) by molecular beam epitaxy

High crystalline quality, vertically aligned AlxGa1-xN nanowire heterostructures are grown on GaN nanowire templates on Si (111) substrates by plasma-assisted molecular beam epitaxy. The nanowires exhibit unique core-shell structures, with enhanced Al compositions in the near-surface region. The emission wavelength can be varied across nearly the entire ultraviolet A (∼3.10–3.94 eV) and B (∼3.94–4.43 eV) spectral range by controlling the Al compositions. Such nanowire structures can exhibit extremely high internal quantum efficiency (up to ∼58%) at room-temperature, which is attributed to the superior carrier confinement offered by the core-shell structures and to the use of defect-free GaN nanowire templates.