The saturation curve for the plasma NH3 pulse (Fig. ) shows differences to the thermal NH3 pulse (Fig. ), suggesting that the thermal reaction is not as strictly self-limited as the plasma reaction. However, such differences are not shown by the residual gas analysis, as both processes show the same pattern of evolution of methane with temperature (Fig. ). The observation that no reaction occurs below 300 °C in the thermal process agrees with previous studies that showed that the NH3 surface reactions with TMA in thermal ALD only occur with reasonable rates at temperatures close to where decomposition of TMA takes place. The presence of hydrogen radicals in the NH3 plasma (Fig. ), suggests that hydrogenation processes of the surface species could play a role in plasma ALD of AlN, which would limit TMA adsorption. This could explain why the plasma process has slightly lower GPCs than the thermal process. The difference in the saturation curves could also be a sign of difference in reaction activity. This is further supported by a higher nucleation delay in the thermal process compared to that in the plasma process (Fig. ).