Low temperature surface preparation of GaN substrates for atomic layer epitaxial growth: Assessment of ex situ preparations

In situ and in vacuo surface studies of in situ and ex situ GaN substrate preparation were conducted to advance fundamental understanding of GaN surface preparation for low temperature atomic layer epitaxial growth. Grazing incidence small angle x-ray scattering (GISAXS) information is complemented with in vacuo x-ray photoelectron spectroscopy and ex situ atomic force microscopy studies to assess different ex situ sample preparation methods to produce the most suitable GaN surface for epitaxy. The authors have determined that a UV-ozone exposure followed by an HF dip produces the cleanest and smoothest GaN surface. They have further determined with GISAXS that subjecting the optimum surface to the established low temperature emulated gallium flash-off atomic level process (ALP) eliminates the need for any nitridation ALP. These ex situ and in situ cleaning preparations result in clean, highly-ordered surfaces that should provide an ideal substrate for high quality crystalline epitaxial films.