The effects of atomic hydrogen (AH) exposure on epi-ready, low-index surface orientations of GaAs at 400 degrees C have been studied using reflection high-energy electron diffraction (RHEED) and scanning tunnelling microscopy (STM). The effective removal of the native oxide by AH from GaAs(0 0 1), (1 10) and (I I I)A substrates was indicated by the gradual appearance of sharp, intense RHEED patterns, typical of those observed normally for clean, flat surfaces. STM images provided direct evidence for the high quality of the as-cleaned surfaces, with further improvements in surface morphology observed after annealing under an As, flux and subsequent buffer growth, as evidenced by significant reductions in surface roughness and step density. Our results show that AH treatment is an effective method for preparing atomically smooth GaAs surfaces for use in an epitaxial growth environment. (c) 2005 Elsevier B.V. All rights reserved.