Homolysis versus β-hydride elimination in the decomposition of trialkylgallium on GaAs(100)

Abstract The decomposition of various surface alkyl groups on GaAs(100), which were generated by dissociative adsorption of the corresponding trialkylgallium precursors R 3 Ga (R=Me, Et, Et- d 5 , n Pr , i Pr , n Bu and t Bu ), was studied by temperature programmed desorption. Two elimination pathways were observed, homolysis and β-hydride elimination. The former reaction results in the formation of alkyl radicals and the latter gives alkene and H 2 as products. On GaAs(100), both reactions are observed in the decomposition of all surface alkyl groups, except for methyl that reacts by homolysis. For each surface alkyl group, homolysis always occurs at slightly lower temperature than β-hydride elimination. Experiments with perdeuterated triethylgallium reveal that surface Et groups do not undergo coupling with coadsorbed deuterium on the surface to form ethane, and that ethane forms in subsequent wall reactions that involve Et radicals. The activation energy E a for homolysis followed the trend Me>Et> n Pr> n Bu> i Pr> t Bu , which reflects the strength of alkyl–surface bonds as well as the increased stability of the alkyl radical. The E a for β-hydride elimination follows closely the E a for homolysis and exhibits similar behavior in terms of magnitude and trend, i.e. Et> n Pr> n Bu≈ i Pr> t Bu , suggesting that breaking the alkyl–surface bond contributes to the activation energy for both homolysis and β-hydride elimination reactions. The alkyl–surface bond energy (Δ H h ) and the heat of reaction for β-hydride elimination (Δ H β ) for all surface alkyls are calculated from the desorption temperatures of their products.