The B3LYP/DZP density functional method was used to calculate the structural, spectral, and thermodynamic characteristics of the R₃GaNR′₃ donor-acceptor complexes and of the products of their dissociation (GaR_x and NR′x) and association ([R₂GaNR′₂]_x and [RGaNR′]_x) (R, R′ = H, CH3; x = 1-3). It was shown that the elimination of RR′ followed by association in the gas phase is the thermodynamically most favorable process over the temperature range from 500 to 1000 K. This suggests that high-temperature association processes in vapors play the main role in the chemical vapor deposition of binary nitrides from the gas phase. A mechanism of the contamination of the nitrides with carbon that postulates the migration of the CH₂ group with the formation of Ga, N, C-containing rings stable in the gas phase was proposed.