MOVPE Mechanisms from studies of specially designed and labelled precursors

Studies of the reaction or decomposition products of precursors for metal o rganic vapour phase epitaxy (MOVPE) do not always give enough information t o allow the unequivocal determination of decomposition or growth mechanisms . By studying deuterium labelled precursors in the presence or absence of t heir protio analogues, other precursors and/or He, H-2, D-2 Or by studying precursors carrying substituents that are designed to give different produc ts if different mechanisms operate, it is possible to draw more definitive conclusions. Using these studies coupled with semi-empirical molecular orbital calculati ons, it is shown that primary arsines decompose by reductive elimination of H-2 followed by beta-abstraction ((BuAsH2)-As-t) or reaction with the pare nt arsine to form RAsH ., which undergoes reductive elimination (PhAsH .), beta-abstraction ((BuAsH)-As-t .) or As-C bond cleavage ((BuAsH)-As-t .). H ex-5-enylarsine has been used to show that adduct formation is not importan t during growth of GaAs. For group 16 dialkyls (R2E, E = S, Se or Te), the predominant decomposition mechanism is homolytic E-C bond cleavage. Subsequent reactions involve abs traction of H from the beta-position of the intact R2E to give alkane, two molecules of alkene E and H . (E = Te or Se). For E = Te, H . does not reac t significantly with (Pr2Te)-Te-i, but for (Bu2Se)-Se-t a short chain-react ion is initiated by H .. The importance of free radicals is confirmed by st udies of (but-2-enyl)(2)Te, (hex-5-enyl)(2)E (E = S, Se, Te), (pent-5-enyl) (2)Te and (hex-5-enyl)SH, as well as of secondary and tertiary analogues. R eactions of the labelled and designed group 16 precursors with Me2M (M = Cd or Zn) are also discussed.