According to our analysis (Figs. and), the averaged diameter of InN crystal grains is 9 nm. This result is comparable to the value of InN grown by ALD using N2 plasma on GaN surface as reported by Woodward et al. A finite inter distance (smaller than 7 nm) between particles together with high particle density of 7.5×10 11 cm -2 indicates that the InN crystal grains are homogeneously distributed on the surface (Fig. ). To better illustrate this coupled gas phase-surface dynamics in our ALD process, we utilized CFD modelling of the gas exchange in the reactor chamber. Fig. shows how the concentration of In species in the gas phase changes near the surface during the TMI pulse and the following N2 purge. With a purge time of 0.1 s, the concentration of In species near the surface is only reduced slightly, while a 2 s purge time afford a significant, but not complete removal of In species on the surface and in the chamber. A 2 s purge reduces the concentration to approximately one-eighth of the concentration just after the TMI pulse. This result coincides with the reduction in particle density observed between 0.1 s and 2 s purge (Figs. and). A purge time of 8 s and longer afforded a surface free from In species except those chemisorbed on the surface. It should be noted that the estimated necessary purge time is heavily dependent on the specific reactor design and carrier gas mass flow rate. Figure . Computational results of TMI concentration before and after the purge started in our growth process. (a) Average concentration over the substrate. The time between -4 to 0 represents the 4 s TMI pulse as indicated by blue shading. The time starting from 0 and afterward refers to the purge step. At 2 s, there is a non-negligible fraction of TMI left, whereas the gas above the substrate is effectively exchanged after 8 s. This is visualized in (b), which shows residual TMI concentration over a cross section of the reactor chamber for different purge times. Note also that the flow field (and hence the required purge time) was relatively unaffected by temperature.