Growth mechanism of catalyst-free [0001] GaN and AlN nanowires on Si by molecular beam epitaxy

Real‐time in‐situ X‐rays scattering experiments were performed to study the nucleation process of GaN nanowires grown by plasma‐assisted molecular beam epitaxy on AlN(0001)/Si(111). From the comparison between the case of nanowires and the case of GaN quantum dots, it is concluded that nanowire precursor islands are completely relaxed from the beginning. Next, based on high resolution electron microscopy analysis, it is demonstrated that relaxation of nanowire precursors is associated to formation of dislocations at the AlN/GaN interface, establishing that three‐dimensional islanding and plastic strain relaxation of GaN are two necessary conditions for nanowire growth. Along the same lines, we demonstrate that three‐dimensional islanding of AlN on SiO2 leads to formation of AlN nanowires with structural and optical properties characteristic of high quality relaxed material (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)