Triple-twin domains in Mg doped GaN wurtzite nanowires: structural and electronicproperties of this zinc-blende-like stacking

Abstract

We report on the effect of Mg doping on the properties of GaN nanowires grownby plasma assisted molecular beam epitaxy. The most significant feature is thepresence of triple-twin domains, the density of which increases with increasing Mgconcentration. The resulting high concentration of misplaced atoms gives rise to localchanges in the crystal structure equivalent to the insertion of three non-relaxedzinc-blende (ZB) atomic cells, which result in quantum wells along the wurtzite (WZ)nanowire growth axis. High resolution electron energy loss spectra were obtainedexactly on the twinned (zinc-blende) and wurtzite planes. These atomically resolvedmeasurements, which allow us to identify modifications in the local density of states,revealed changes in the band to band electronic transition energy from 3.4 eV forwurtzite to 3.2 eV in the twinned lattice regions. These results are in good agreementwith specific ab initio atomistic simulations and demonstrate that the redshiftobserved in previous photoluminescence analyses is directly related to the presenceof these zinc-blende domains, opening up new possibilities for band-structureengineering.