Spectroscopic identification of the reaction intermediates in the thermal decomposition of trimethylindium at GaAs(100) surfaces

High resolution electron energy loss spectroscopy (HREELS) has been used to study the adsorption and thermal decomposition of trimethylindium (TMIn) on Ga-terminated GaAs(100) surfaces. HREEL spectra recorded for adsorption at room temperature are dominated by strong CH3 deformation and stretching modes and indicate that the surface species is based on methyl groups, The intensities of these bands decrease with increasing temperature consistent with a primary decomposition route involving the loss of CH3 groups from the surface. A small upward shift in the frequency of the symmetric and asymmetric CH3 deformation modes is also observed with increasing temperature and indicates that decomposition takes place via an exchange reaction in which CH3 groups switch from In to Ga due to the stronger Ga-C bond. At temperatures greater than 350 degrees C, the spectra are dominated by CH2 rocking, deformation and stretching vibrations. The presence of a surface methylene species at elevated temperatures suggests a second, minority decomposition pathway which involves dehydrogenation of surface CH3 groups to CH2.