APPLICATIONS OF MBMS AND SURFACE SPECTROSCOPIC TECHNIQUES IN THE STUDY OF REACTION-MECHANISMS IN CBE - INVESTIGATIONS OF THE REACTIVITY OF TRITERTIARYBUTYLGALLIUM AND TRIISOBUTYLGALLIUM AS ALTERNATIVE PRECURSORS FOR EPILAYER GROWTH

Current approaches to the study of reaction mechanisms in CBE and investigations of the potential of triisobutylgallium and tritertiarybutylgallium as novel CBE precursors are reviewed. Surface spectroscopic techniques indicate that adsorbed iso-butyl radicals decompose to produce gaseous butene and hydrogen at significantly lower temperatures than in the corresponding process for ethyl radicals on GaAs, resulting in lowered growth temperatures and low temperature C incorporation levels in comparison to the results obtained with triethylgallium. A beta-methyl migration occurs at higher temperatures causing C to deposit irreversibly on the surface in the presence of Al. Lowered temperatures for the beta-hydride elimination reaction are also observed for adsorbed tertiarybutyl radicals and the absence of beta-methyl groups avoids the facile C deposition process seen for iso-butyl. These potential advantages associated with tertiarybutyl ligands cannot be realized straightforwardly in CBE using tritertiarybutylgallium however, since steric crowding effects result in the inefficient total dissociation of the adsorbing precursor molecule.