Fabrication of non-polar AlN films by ICP etching and overgrowth by MBE

Resumen

AlN films, a-plane and m-plane oriented, were obtained by molecular beam epitaxy overgrowth on GaN isolated nanopillars following a three-step process involving: dry etching of a GaN buffer layer to obtain nanopillars; GaN overgrowth on nanopillars and finally AlN overgrowth until nanocrystals coalescence. The resulting a-plane AlN layer shows a roughness, with a RMS of 90 nm over a 5 x 5 mu m2, higher than the m-plane AlN one with a RMS of 35 nm over the same area, which shows much better morphological quality. Plan-view transmission electron microscopy images of the m-plane AlN layer reveal stacking faults, but threading dislocations are barely seen. Cross-sectional transmission electron microscopy image shows stacking faults in bunches running through the sample volume, separated by areas (50 to 100 nm wide) which seem free of them.