Inelastic light scattering spectroscopy of semiconductor nitride nanocolumns

A review of inelastic light scattering measurements on group III-nitride nanocolumns grown by molecular beam epitaxy is presented. The nanocolumns are hexagonal, high quality single crystals with diameters in the range of 20 to 100 run, with no traces of extended defects. GaN nanocolumns grown on bare Si substrates with both (111) and (100) orientation display narrow phonon peaks, indicating the absence of strain inhomogeneities. This opens the possibility of efficient integration of the nanocolumns as optoelectronic devices with the complementary metal oxide semiconductor technology. Measurements of the E(2) phonon frequency on AlGaN nanocolumns indicate a linear dependence of the Al concentration on the Al relative flux, up to 60%. The E(2) peak width increases with Al content due to phonon damping by alloy scattering. Inelastic light scattering measurements in InN nanocolumns display a coupled LO phonon-plasmon mode together with uncoupled phonons. The coupled mode is not observed in a reference compact sample. The origin of the coupled mode is attributed to spontaneous accumulation of electrons at the lateral surfaces of the nanocolunms. The presence of free electrons in the nanocolumns is confirmed by infrared reflectance measurements. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.