Kinetics of the reaction between trimethylgallium and arsine

Abstract

The kinetics of the reaction between trimethylgallium (TMGa) and AsH3 were studied in a flow tube reactor with D2 as the carrier gas and using a time-of-flight mass spectrometer to analyze the products. Addition of TMGa accelerates AsH3 decomposition. Like wise, AsH3 lowers the pyrolysis temperature of TMGa. The data from the decomposition at a series of V/III ratios shows that the stoichiometry is exactly 1:1 Experiments using a methyl radical scavenger show that gas phase free radical reactions are not important in the temperature range studied. The variation in rate constant with surface area shows that the rate determining step is predominatly heterogeneous. The only product in D2 is CH4, so there is no independent gas phase decomposition of TMGa. The lack of H2 and C2H6 indicates that independent surface pyrolysis of either TMGa or AsH3 does not occur. Two mechanisms are consistent with our data: (i) heterogeneous decomposition of an adduct formed in the gas phase and (ii) a Langmuir-Hinshelwood mechanism consisting of reaction between undecomposed adsorbed TMGa and AsH3 molecules. Based on measurements of growth rate versus pressure of TMGa and AsH3, the latter is the most likely pathway.