Thermochemistry of alkylarsine compounds used as arsenic precursors in metalorganic vapor phase epitaxy

Abstract

Despite their increased safety, alkylarsine compounds have not generally replaced arsine (AsH3) in the metalorganic vapor phase epitaxy (MOVPE) of GaAs because of carbon incorporation and high background doping levels. We have studied the thermal decomposition of AsH3 and its alkyl derivatives (methyl, ethyl, and butyl compounds) to determine the impact of the thermochemistry on growth processes. The thermal stability of the As-precursor compounds was found to decrease in the order AsH3>MenAsH3−n >Et3As>t-BuAsH2. We report the first evidence for production of diarsine (As2H4) from t-BuAsH2 and for formation of lower substituted methylarsine homologs from Me3As and Me2AsH. The presence of these species is strong evidence that decomposition of the alkylarsines occurs via a free-radical mechanism. Formation of carbon-free arsenic products appears to be the key difference between t-BuAsH2 and the more highly substituted alkylarsines in attaining high quality films by MOVPE.