In situ characterisation of epiready III-V substrates for MOVPE

The use of the term epiready in relation to III-V substrates in MOVPE is il l defined and poorly understood. In this paper we attempt to clarify some o f the issues associated with the term epiready, in particular, the thicknes s and distribution of native oxide on the surface of a GaAs wafer. The surf ace quality of a wafer is established at three stages, fresh from the packe t, oxide removed, and after growth. The surface is assessed by means of ato mic force microscopy on a microscopic level and laser light scattering and oxide thickness mapping on a macroscopic scale. GaAs substrates from long-t erm storage are also examined. It is shown that even long-term stored wafer s (in excess of six years) with quite thick native oxide layers can be succ essfully deoxidised to give atomically flat terraces and can subsequently b e used for successful homoepitaxial growth provided that atomic hydrogen (i n this case, from the arsenic precursor) is used in the deoxidation stage. No difference between various manufacturers substrates has been found in re spect to storage and subsequent use, nor has any difference been establishe d between doped and undoped wafers. (C) 2000 Elsevier Science B.V. All righ ts reserved.