GaN quantum discs embedded in AlGaN nanocolumns with outstanding crystal quality and very high luminescence efficiency were grown on Si͑111͒ substrates by plasma-assisted molecular beam epitaxy under highly N-rich conditions. Nanocolumns with diameters in the range of 30-150 nm, with no traces of any extended defects, as confirmed by transmission electron microscopy, were obtained. GaN quantum discs, 2 and 4 nm thick, were grown embedded in AlGaN nanocolumns by switching on and off the Al flux during variable time spans. Strong optical emissions from GaN quantum discs, observed by photoluminescence and cathodoluminescence measurements, reveal quantum confinement effects. While Raman data indicate that the nanocolumns are fully relaxed, the quantum discs appear to be fully strained. These nanostructures have a high potential for application in efficient vertical cavity emitters.

High quality AlGaN nanocolumns have been grown by molecular beam epitaxy on Si(111) substrates. Scanning Electron Microscopy micrographs show hexagonal, single crystal columns with diameters in the range of 30 to 60 nm. The nominal Al content of the nanocolumns was changed from 16% to 40% by selecting the flux ratio between the Al and the total III‐element, while keeping the growth temperature and the active nitrogen constant. The nominal values of the Al content are consistently lower than the experimental ones, most likely due to the high Ga desorption rates at the growth temperature. The Al composition trend versus the Al flux is consistent with the E2 phonon energy values measured by inelastic light scattering. These results open the possibility to grow high quality low dimensional structures based on AlGaN/GaN/AlGaN heterocolumns for basic studies and device applications.

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Pyrite thin films have been grown by sulphuration of Fe thin films and their Seebeck coefficient has been measured as a function of the sulphuration temperature in the range 370-720 K. Films appear to be p-type (positive Seebeck coefficient) for sulphuration temperatures higher than 450 K The evolution of the coefficient with the sulphuration temperature has been qualitatively correlated with the crystallization process that the films suffer on increasing that temperature. According to our analysis, the highest value of the Seebeck coefficient obtained in our measurements (S ≈ 80 µV K −1 ) should correspond to non-stoichiometric crystallized pyrite films formed by spheroidal grains.

This work reports on the characterization of hexagonal, single crystal AlGaN nanocolumns with diameters in the range of 30 to 100 nm grown by molecular beam epitaxy on Si(111) substrates. The change of the flux ratio between the Al and the total III-element controls the alloy composition. The Al composition trend versus the Al flux is consistent both with the E 2 phonon energy values measured by inelastic light scattering and the luminescence emission peaks position. High quality low dimensional AlGaN/GaN/AlGaN heterostructures with five GaN quantum discs, 2 and 4 nm thick, embedded into the AlGaN columns, were designed in order to study the quantum confinement effects.