Résumé
Self-organised nanocolumnar systems based on group-III nitride semiconductors present numerous original characteristics, of which the absence of extended defects is certainly the most promising for optoelectronic applications. Nevertheless, another feature, namely the large surface/volume ratio of nanocolumns with typical diameters in the 20-60 nm range, deserves further investigation. We focus for this talk on luminescence properties of GaN and InGaN nanocolumns grown by plasma-assisted molecular beam epitaxy on silicon (111) substrates. Two cases of surface-related properties will be addressed: 1) The origin of the photoluminescence doublet at 3.450-3.456 eV will be discussed in terms of the particular physics of donor-bound excitons, when donor nuclei sit within a layer of ~10 nm from the side surface of a GaN nanocolumn. Detailed studies of power- and temperature-dependent PL spectroscopy will be analyzed. 2) Changes in photoluminescence properties of nitride nanocolumnar systems placed in various environments (vacuum, air...) will be presented and discussed in terms of photochemical effects and their consequences on the dynamics of excitonic recombination.