PROBING SURFACE CHEMICAL PROCESSES DURING EPITAXIAL SEMICONDUCTOR CRYSTAL-GROWTH AT NEAR-ATMOSPHERIC PRESSURES USING PHOTON-BASED TECHNIQUES

It is demonstrated here that for the study of epitaxial semiconductor crystal growth from vapour-phase precursors, photon-based methods may be applied under true 'in situ' conditions and can, where appropriate, reveal a great deal regarding the nature of the growing surface. Whil e several techniques exist which may probe the gaseous phase, the stud y of the surface phase under conditions of high pressures (up to 1000 mbar) and high temperatures (up to 1000 K) is far from trivial. This p aper sets out to emphasise recent developments in technique which perm it the study of the surface phase during epitaxial crystal growth. Dat a are presented for several semiconductor/ substrate systems obtained using the linear technique of reflectance anisotropy and the non-linea r technique of optical second-harmonic generation (SHG). In particular , the technique of reflectance anisotropy is shown to be a very powerf ul probe of surface stoichiometry, real-time monitoring of layer-by-la yer growth processes, adsorption and desorption kinetics and also the detection of surface reconstructions that occur under high vacuum and near-atmospheric pressure conditions. For the SHG technique it is show n that the application of this method to centroasymmetric substrates s uch as GaAs is not trivial, yet under certain conditions surface SHG r esponses can be observed which are directly related to the structure o f the surface layers. While the data presented are for special epitaxi al semiconductor systems, throughout the paper emphasis is placed upon the applicability of the experimental approach towards the study of c rystal growth systems in general.