Laser molecular beam epitaxy of vertically self-assembled GaN nanorods on Ta metal: Role of growth temperature and laser repetition rate

Self-aligned GaN nanorod assembly directly grown on metal foil substrates is very attractive for developing flexible devices. In this report we have investigated the effect of growth temperature (500-700 ᵒC) and laser repetition rate (10-30 Hz) on the formation, structural, morphological and optical properties of GaN nanorods, grown on flexible Ta metal foil by laser molecular beam epitaxy (LMBE). It is found that the growth temperature plays a critical role in the formation of vertically self-aligned growth of GaN nanorods. The high temperature growth at 700 C yielded a highly dense and vertically-aligned nanorod ensemble on Ta foil. The nanorod alignment is highly uniform across the sample and no tilt was observed irrespective of the polycrystalline nature of the Ta foil. The GaN nanorods are characterized for its hexagonal wurtzite structure and c-axis oriented growth. The laser repetition rate on the growth GaN at 700 C altered only the dimension and aerial density of GaN nanorods but did not affect the nanorod alignment. The grown GaN nanorod ensemble exhibits high optical quality with an intense and sharp near band-edge emission in the UV region and negligible yellow band emission. The growth of GaN nanorod on Ta foil is observed to be self-driven without being influenced by the substrate nature.