DFT Modeling of Chemical Vapor Deposition of GaN from Organogallium Precursors. 1. Thermodynamics of Elimination Reactions

The thermochemistry of dissociation and elimination reactions of organogallium precursors for the GaN chemical vapor deposition (CVD) is studied at the hybrid Hartree−Fock/density functional level of theory (B3LYP/pVDZ). Geometries, relative energies, vibrational frequencies of R x GaNR‘ x species, and their dissociation products (NR x, GaR x, x = 1−3; (R, R‘ = H, CH 3 ) are presented. Methane elimination from the source adducts is exothermic at standard conditions, while hydrogen elimination is endothermic. Both for R = H, CH 3 elimination reactions are predicted to be more favorable compared to dissociation into components, in contrast to the halogen containing precursors. The Ga−N bond dissociation enthalpies (kJ mol -1 ) are the highest for R 2 GaNR‘ 2 compounds (313−382), followed by RGaNR‘ (196−266); and for donor−acceptor complexes R 3 GaNR‘ 3 (56−100) they are the lowest. (CH 3 ) x GaNH x isomers are more than 50 kJ mol -1 lower in energy than H x GaN(CH 3 ) x species, but the formation of Ga−H and N−H bonds is the thermodynamically most favorable process. Hence, the replacement of alkyl groups might be viable during the CVD process from trimethylgallium and ammonia.