A COMPARATIVE-STUDY OF THE ADSORPTION AND THERMAL-DECOMPOSITION OF TRIETHYLGALLIUM AND TRIMETHYLGALLIUM AT GAAS(100) SURFACES STUDIED BY ELECTRON-ENERGY-LOSS SPECTROSCOPY

High resolution electron energy loss spectroscopy (HREELS) has been us ed to study the adsorption and thermal decomposition of triethylgalliu m (TEGa) and trimethylgallium (TMGa) at Ga-terminated GaAs(100) surfac es, HREEL spectra recorded for adsorption of TEGa at room temperature show that the dominant surface species is based on intact ethyl (C2H5) groups. The surface species, which is likely to be diethylgallium (DE Ga), is stable up to 250 degrees C. Heating to 400 degrees C results i n the complete decomposition of the molecule via the facile beta-elimi nation mechanism. For TMGa adsorption, HREEL spectra indicate that the stable surface species at room temperature is based on intact methyl (CH3) groups, and is likely to be a dimethylgallium (DMGa) species. De composition of this species occurs with increasing temperature and inv olves the loss of CH3 groups from the surface. In contrast to the clea n decomposition of TEGa, a surface methylene (CH2) species is also ide ntified for TMGa at elevated temperatures and suggests an additional d ecomposition pathway involving loss of hydrogen from adsorbed CH3 grou ps. The presence of this stable species in the case of TMGa, and not T EGa, is a possible explanation for the high carbon incorporation level s found in GaAs grown by chemical beam epitaxy (CBE) from this precurs or.