Kinetics of metal organic-ammonia adduct decomposition: implications for group-III nitride MOCVD.

We have used infrared spectroscopy to investigate the decomposition of the gas-phase (Me)(3)M:NH(3) (M = Al, Ga, In) adducts from room temperature to 573 K, at reactant concentrations in the nominal range used for Al(Ga,In)N metal organic chemical vapor deposition. At 473-523 K TMAl:NH(3) decomposes quantitatively to yield (Me(2))AlNH(2) and CH(4). Comparison of the experimental and theoretical spectra indicates that the majority of the aluminum metal organic product exists in dimer form, i.e., [(Me(2))AlNH(2)](2). The decomposition reaction exhibits unimolecular decomposition kinetics with rate constant parameters of nu = 1 x 10(12) s(-1) and E(a) = 25.7 kcal/mol. At temperatures <543 K, TMGa + NH(3) and TMIn + NH(3) mixtures are dominated by reversible adduct formation-dissociation with no detectable quantities of CH(4) produced. At 574 K a small amount of decomposition is observed in TMGa + NH(3) mixtures, which can be explained by a simple kinetic model that includes the effect of adduct equilibrium. Results demonstrate that the (Me)(3)Al:NH(3) decomposition rate is fast enough to contribute to the early stages of a concerted parasitic chemical reaction mechanism, but the (Me)(3)Ga:NH(3) decomposition rate is too slow.