Optical properties of basal plane stacking faults in AlN nanowires

It is shown that depending on growth conditions, cathodoluminescence and photoluminescence spectra of AlN nanowires grown by plasma-assisted molecular beam epitaxy exhibit a peculiar optical signature around 5.85 eV. Several contributions to this peak can be identified, with a large variability in energy from nanowire to nanowire. We show that these peaks are correlated with the presence of I1 basal stacking faults (BSFs), crossing the entire diameter of nanowires. The formation of BSFs is assigned to the specific kinetics of Al and N adatoms when using migration enhanced epitaxy technique. By analogy with previous observations in GaN, we propose that I1 BSFs behave as zinc-blende quantum wells in a wurzite (WZ) matrix. Temperature and power dependence studies of the optical properties of these quantum wells by cathodoluminescence and photoluminescence are consistent with exciton coupling to randomly distributed donors in the WZ matrix and also suggest an inter-BSF coupling depending on their density.