Sub-meV linewidth of excitonic luminescence in single GaN nanowires: Direct evidence for surface excitons

Abstract

We investigate the low-temperature photoluminescence of GaN nanowires grown catalyst free on Si(111). For single nanowires dispersed on Si(111), we observe excitonic transitions with linewidths below $300\text{ }\ensuremath{\mu}\text{eV}$ and at energies clearly above the donor-bound exciton in the bulk. We show that these transitions are due to donor-bound excitons close to the surface. The broadening of about 3 meV observed for the nanowire ensemble is shown to be a natural consequence of the energy dispersion of bound-exciton states as a function of their distance from the surface.