Reaction Pathways for Model II-VI Precursors: A Computational Study

摘要

A computational study of the reactions of model II-VI precursors, MH_2 (M = Zn, Cd, Hg) and H_2E (E = O, S, Se, Te), is reported. The present computations yield several results of relevance to OMVPE of II-VI materials from MR_2/ER'_2 precursors. Adduct formation is feasible at low temperatures, in line with recent experiments, but not at higher temperatures common in II-VI OMVPE. Calculations suggest that adducts are most likely to form after elimination has resulted in replacement of hydride with hydroxide ligands (in our model) or alkyl with alkoxide ligands (in larger modes). The overall reaction MH_2 + 2H_2E -> M(EH)_2 is generally more favorable, kinetically and thermodynamically, for lighter metals and heavier elements. On the basis of calculated thermodynamic and kinetic quantities, we conclude that the preferred pathway from reactants (MH_2 + 2H_2E), except for M = Hg and E = Te, to an M(EH)_2 intermediate is by way of a 1:2 adduct (or a similar portion of the potential energy surface in the absence of a bound adduct) followed by two successive H_2 eliminations, in preference to the alternative in which adduct formation and H_2 elimination occur in succession.