DFT modeling of chemical vapor deposition of GaN from organogallium precursors. 1. Thermodynamics of elimination reactions

The thermochemistry of dissociation and elimination reactions of organogall ium precursors for the GaN chemical vapor deposition (CVD) is studied at th e hybrid Hartree-Foc/density functional level of theory (B3LYP/pVDZ). Geome tries, relative energies, vibrational frequencies of RxGaNR ' (x) species, and their dissociation products (NRx, GaRx, x = 1-3; (R, R ' = H, CH3)) are presented. Methane elimination from the source adducts is exothermic at st andard conditions, while hydrogen elimination is endothermic. Both for R = H, CH3 elimination reactions are predicted to be more favorable compared to dissociation into components, in contrast to the halogen containing precur sors, The Ga-N bond dissociation enthalpies (kJ mol(-1)) are the highest fo r R2GaNR ' (2) compounds (313-382), followed by RGaNR ' (196-266); and for donor-acceptor complexes R3GaNR ' (3) (56-100) they are the lowest. (CH3)(x )GaNHx isomers are more than 50 kJ mol(-1) lower in energy than H,GaN(CH3), 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 via ble during the CVD process from trimethylgallium and ammonia.