Regrowth of hexagonal GaN pyramids at the tops of GaN nanocolumn arrays by plasma-assisted RF-MBE

Abstract

Well-aligned hexagonal GaN pyramids on the top of GaN nanocolumn arrays have been achieved successfully by the two-step method. Fistly, the well-aligned nanocolumn arrays are fabricated by UV-curing nanoimprint lithography. Next, the GaN pyramids are regrown on the top of GaN nanocolumn arrays by RF-plasma assisted molecular beam epitaxy. The as-grown GaN nanostructures are characterized by the in-situ reflection high-energy electron diffraction (RHEED), field emission scanning electron microscopy (FESEM) and photoluminescence (PL) spectrum. The results demonstrate that the GaN pyramid/nanocolumn arrays are formed with extremely smooth facets and sharp tips, the epitaxial growth of pyramids on the top o f columns cause the columns to evolve from spherical to quasi-hexagonal shape. The V/III ratio has a great effect on the lateral growth of pyramid, the V/III ratio of 4:1 is beneficial to the growth of (1012) facet, while that of 8:1 is the (2023) facets. And the formation mechanism of GaN pyramids is discussed.