Résumé
The low pressure MOVPE growth process of GaN deposited onto GaN buffer layers on sapphire substrates is studied in detail. The relevant growth parameters are identified, and their influences are studied. These include the influence of the sapphire nitridation, the growth of the GaN buffer layer and its subsequent thermal treatment, and the growth parameters of the GaN epilayer (growth temperature, precursor flow rates, V/III ratio, etc.). Low temperature photoluminescence was mainly used to investigate the layer quality and, as a result of this optimization study, we have been able to reproducibly grow layers which have a 2 K photoluminescence dominated by the free exciton. (C) 1997 Elsevier Science S.A.