Ordered arrays of defect-free GaN nanocolumns with very narrow excitonic emission line width

Abstract

Ordered arrays of very high quality, defect-free GaN nanocolumns were achieved by selective area growth following a two step process involving nanopillar dry etching (top down) and overgrowth by Molecular Beam Epitaxy (bottom up). A study by transmission electron microscopy, over more than 50 individual nanocolumns, confirmed the absence of extended defects, such as dislocations, polarity inversion domain boundaries and stacking faults. Low temperature (10 K) photoluminescence spectrum is dominated by a donor-bound exciton emission line at 3.472 eV with a line width of 0.5 meV. In addition, a distinct emission line from the free-exciton A is observed at 3.479 eV. No traces of emission lines, either at 2.3 eV (Yellow Band); 3.45 eV (also labeled as UX line and recently linked to polarity inversion domain boundaries); or 3.42 eV (stacking faults) were observed.