THE USE OF HEX-ENYLARSINE AS A CHEMICALLY DESIGNED PRECURSOR TO PROBETHE MECHANISMS OF THE METALORGANIC VAPOR-PHASE EPITAXY GROWTH OF GALLIUM-ARSENIDE - CONSEQUENCES FOR REACTOR DESIGN

Ex-situ Fourier transform infrared spectroscopy has been employed to s tudy the mechanisms of the metalorganic vapour phase epitaxy growth of GaAs, using hex-5-enylarsine and trimethylgallium as precursors. Hex- 5-enylarsine was synthesized for the purpose of distinguishing between reductive elimination, free radical and beta-hydrogen elimination rea ctions since all three pathways are theoretically available for its de composition. However, the reaction under MOVPE conditions is not as si mple as envisaged in that fragmentation of the hex-5-enyl alkene chain competes effectively with C-As bond cleavage as a decomposition pathw ay. Thus for hex-5-enylarsine in dihydrogen decomposition is observed to commence at temperatures of ca. 500-degrees-C yielding as yet unass igned alkylarsines, methane and some ethene as products. At higher tem peratures ethane, propane and propene are formed while at very high te mperatures (> 700-degrees-C) there is evidence for the formation of et hyne and 1,3-butadiene. In the presence of trimethylgallium (TMGa), an involatile solid forms at room temperature via the elimination of met hane, strongly supporting the proposal that gas-phase adduct formation occurs as the primary process. At higher temperatures, ca. 350-degree s-C, this solid begins to decompose yielding the alkylarsines noted ab ove. In addition, methylarsine and dimethylarsine are formed, together with methylene cyclopentane and cyclohexane. The appearance of these latter products appears to correlate with the onset of decomposition o f TMGa and is attributed to a mechanism involving the formation of a r adical intermediate which may then undergo 1,5 or 1,6 cyclization.