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 used to study the adsorption and thermal decomposition of triethylgallium (TEGa) and trimethylgallium (TMGa) at Ga-terminated GaAs(100) surfaces. 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 (DEGa), is stable up to 250°C. Heating to 400°C results in the complete decomposition of the molecule via the facile β-elimination 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. Decomposition of this species occurs with increasing temperature and involves the loss of CH3 groups from the surface. In contrast to the clean decomposition of TEGa, a surface methylene (CH2) species is also identified for TMGa at elevated temperatures and suggests an additional decomposition pathway involving loss of hydrogen from adsorbed CH3 groups. The presence of this stable species in the case of TMGa, and not TEGa, is a possible explanation for the high carbon incorporation levels found in GaAs grown by chemical beam epitaxy (CBE) from this precursor.