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

Abstract

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 ; 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.

Nature of the parasitic chemistry during AlGaInN OMVPE

“…Further CH 4 elimination and association (oligomerization) may occur, eventually leading to clusters (or nuclei) large enough to support growth by a CVD process. One aspect of the concerted path-A is that it involves reactions with relatively low activation energy (o40 kcal/mol) [12][13][14][15]. Mihopolous et al [12] used a mechanism of this type, with thermophoresis considerations, to explain many AlN OMVPE observations.…”

Growth mechanism of catalyst‐ and template‐free InN nanorods

“…The strong intramolecular H-Cl hydrogen bonding and dipoledipole interactions are known to favor the formation of larger oligomer species [21]. The extent of the oligomerization process has not been known explicitly, but Timoshkin reported that the generation of gas phase [HGaNH] n clusters even with oligomerization degree n ≥ 60 is viable in his theoretical works [30,31]. When the Cl/In ratio becomes much higher than 3, InN growth becomes unfavorable because of the enhanced HCl etching by excess HCl (g).…”

Materials Chemistry of Group 13 Nitrides

“…Therefore, the majority of computational investigations have dealt with the chemistry of ammonia adducts and their decomposition products. A wealth of thermodynamic information has been calculated at the DFT level by Timoshkin et al [80][81][82]. The structures and relative energies of a number of possible non-radical gas phase species have been calculated, including gallium amides R 2 GaNR 2 (with R, R = Me, H) and their oligomers.…”