Nanoheteroepitaxy of GaN on AlN/Si(111) nanorods fabricated by nanosphere lithography

Nanoheteroepitaxy (NHE) of GaN on an AlN/Si(111) nanorod structure was investigated by metal-organic chemical vapor deposition. Silica nanosphere lithography was employed to fabricate a periodic hexagonal nanorod array with a narrow gap of 30 nm between the nanorods. We were successful in obtaining a fully coalesced GaN film on the AlN/Si(111) nanorod structure. Transmission electron microscopy revealed that threading dislocation (TD) bending and termination by stacking faults occurred near the interface between GaN and the AlN/Si(111) nanorods, resulting in the reduction of TD density for the NHE GaN layer. The full width at half-maximum of the X-ray rocking curve for (102) plane of the NHE GaN was found to decrease down to 728 arcsec from 1005 arcsec for the GaN layer on a planar AlN/Si(111) substrate, indicating that the crystalline quality of the NHE GaN was improved. Also, micro-Raman measurement showed that tensile stress in the NHE GaN layer was reduced significantly as much as 70% by introducing air voids between the nanorods.