(i) reductive elimination, where TMA undergoes reductive elimination to produce monomethyl aluminum on the surface and ethane gas; this pathway does not involve the removal of surface hydrogen atoms, (ii) methyl protonation followed by reductive elimination where TMA interacts with two surface hydrogen atoms, leading to the formation of monomethyl aluminum on the surface, along with methane and ethane gas, surface hydrogen atoms are transferred to the methyl groups during this decomposition pathway, and (iii) methyl protonation twice where TMA reacts with a surface hydrogen atom to generate an aluminum adatom, methane and ethane gas, this process involves the removal of hydrogen atoms from the surface during decomposition. These pathways were found to be pivotal in determining surface coverage, hydrogen removal, and the overall AlN film-growth efficiency. The DFT study found that TMA would most likely adsorb as a Lewis adduct on the -NH2 covered surface and decompose via reductive elimination or methyl protonation pathways, with the proximity to previously adsorbed TMA molecules influencing the decomposition pathway. The ratio of the different decomposition pathways was suggested to affect the growth per cycle (GPC) by influencing the saturation coverage of the surface. The relative concentrations of TMA molecules decomposing via the three pathways determine the availability of surface sites for TMA adsorption. If the dominant pathway is methyl protonation, which removes surface hydrogen and allows for additional TMA adsorption sites, the GPC may increase due to higher surface saturation coverage. On the other hand, if the dominant pathway is reductive elimination, which does not involve hydrogen removal, the GPC may be lower as the surface may become saturated with hydrogen atoms, limiting additional TMA adsorption sites.