Structural and optical characterization of intrinsic GaN nanocolumns

The morphology and optical properties of GaN nanocolumns grown on Si( I I I) and sapphire substrates by plasma-assisted molecular beam epitaxy, are studied by photoluminescence. Raman scattering, scanning electron microscopy and cathodoluminescence. The nanocolumns grow along the [0 0 01] direction and exhibit high-crystal line quality, Their section is hexagonal with diameters between 450 and 1250 Angstrom. The photoluminescence spectrum is composed by two excitonic peaks at 3,471 and 3.452 eV. and three broad emissions at lower energy. Cathodoluminescence images show that the excitonic emissions originate at the upper nanocolumns body while the low-energy peaks are originated at the 'bulk' material at the bottom of the nanocolumns. The low-energy emissions are related to defects at the interface between the columns and the substrate. (C) 2002 Elsevier Science B.V. All rights reserved.