1.8 μ m thick high-quality cubic GaN film was successfully grown on GaAs (100) using an ultra-thin, low-temperature GaN buffer layer by a plasma-assisted molecular beam epitaxy. The 'as-grown' low-temperature buffer layer was amorphous and ultra-thin (∼ 6&ANGS;), which is a necessity condition to grow a pure cubic GaN epilayer. FWHM of X-ray rocking curve (c-GaN (200) diffraction) is as narrow as 28.7 arcmin. © 2005 Elsevier B.V. All rights reserved.