DFT suggested that a surface chemistry fully dominated by ligand exchange, render a GPC on the (001) surface of AlN of 2.49 Å/cycle, while a surface chemistry dominated by reductive elimination render a third of that GPC, i.e., 0.83 Å/cycle. Our experiments, with growth on the (100); (002); and (101) AlN surfaces, with increasing TMA and NH3 plasma exposure times show a self-limiting surface chemistry for both half reactions (Fig. ) with 0.83 and ∼1 Å/cycle at saturation for the plasma and thermal processes, respectively. This suggests that, during the TMA pulse, the surface chemistry is highly dominated by reductive elimination of methyl groups as methane, rendering monomethyl aluminum on the surface. Methane was also detected by mass spectrometry. The change in CH4 evolution with temperature, Fig. , suggests that thermal activation is stronger from the TMA pulse than the NH3 pulse. Our estimated activation energies are in line with this, with the highest activation energy for the methane evolution during the TMA pulse. The much lower intensity of the unprotonated methyl ligand, CH3 at m/z = 15 and its possible recombination product C2H6 at m/z = 30 (two methyls can combine and produce ethane in a 'termination' type of reaction), compared to methane at m/z = 16 in Fig. , aligns with the anticipated reaction mechanism where the adduct ligand participates in the reaction, forming CH4, rather than separating independently as • CH3.