The influence of AlN buffer over the polarity and the nucleation of self-organized GaN nanowires

We experimentally investigate the influence of AlN buffer growth on the nucleation and the polarity of a self-organized assembly of GaN nanowires (NWs) grown on Si. Two complementary growth mechanisms for AlN buffer deposited on Si are demonstrated. Both emphasize the aggregation of Si on the AlN surface and the growth of large cubic crystallites, namely, AlN pedestals. Further growths of GaN NWs assembly reveal that the GaN 2D layer found at the bottom of the NW assembly is the result of the coalescence of Ga-polar pyramids, whereas AlN pedestals are observed as preferential but not exclusive NW nucleation sites. NWs are N-polar or exhibit inversion domains with a Ga-polar core/N-polar shell structure. This suggests that N-polarity is a necessary condition to trigger NW self-organized nucleation due to a different facets energy hierarchy between the Ga- and the N-polar sides. (C) 2015 AIP Publishing LLC.