## 3 Results
### NH\({}_{3}\) Adsorption on PC 1-2 Structure  
When TMG is adsorbed on the Si\({}_{2}\)-NH surface by consuming a one-adsorption site, the product of the reaction would be the PC 1-2 + CH\({}_{4}\) structure (Figure 5). In this case, we simulated the adsorption of NH\({}_{3}\) on this structure. The reaction mechanism of the nitridation step is described in Figure 6, where the PC 1-2 + CH\({}_{4}\) structure is used as the substrate. The reaction starts from the adsorption 1-3 stage (a), where the first NH\({}_{3}\) molecule approaches the Ga atom at a distance of 2.13 A. Then, in the transition 1-3 stage (b), the Ga and N3 atom distances are reduced to 1.99 A, and the Ga-C2 bond is broken at 2.29 A. The Ga-N3 bond is formed with a length of 1.83 A in the PC 1-3 stage (c), while a CH4 molecule is released as a reaction by-product in the PC 1-3 + CH4 stage (d). Then in the adsorption 1-4 stage (e), the second NH\({}_{3}\) molecule approaches the Ga atom at a distance of 2.11 A. In the transition 1-4 stage (f), the Ga and N4 atom distances are reduced to 1.98 A, and the Ga-C3 bond is broken at 2.27 A. The Ga-N4 bond is formed with a length of 1.86 A in the PC 1-4 stage (g), while a CH4 molecule is released as a reaction by-product in the PC 1-4 + CH4 stage (h). The N4-Ga-N3 species is formed in the PC 1-4 + CH4 stage as a final product, while the second CH4 by-product is released. The energy profile for this reaction is shown in Figure 6. The two NH\({}_{3}\) molecules were adsorbed on the surface according to similar mechanisms. Therefore, they have similar reaction pathways. Energies of 0.71 and 0.74 eV were released when the first and second NH\({}_{3}\) molecules approached the surface in the adsorption 1-3 and 1-4 stages, respectively. Activation barriers of 1.88 and 1.92 eV are needed to overcome the transition stages, TS 1-3 and TS 1-4, respectively. NH\({}_{3}\) adsorptions were exothermic, where the final product (PC 1-4) structure was stably formed at 0.94 eV below the reactant level. The NH\({}_{3}\) molecules were adsorbed on the surface with activation barriers slightly less than the barrier for TMG adsorption on the Si-NH\({}_{2}\) surface (2.00 eV), indicating that the nitridation processes were preceded by a more facile reaction. In addition, the relative energies at transition stages (TS 1-3 and TS 1-4) were substantially less than the relative energy at TS 1-2 (1.65 eV), indicating that the nitridation process can occur at a lower process temperature. This work suggested that if TMG were adsorbed on the Si\({}_{2}\)-NH surface by consuming a one-adsorption site, the residual Ga-C bonds would be eliminated in the nitridation steps, which have lower energy barriers and lower process temperatures compared to the TMG adsorbed on the Si-NH\({}_{2}\) surface. For other cases, Figure 5 shows the reaction pathways leading to possible four-product structures that can be generated by the adsorption of TMG on Si\({}_{2}\)-NH and Si-NH\({}_{2}\) passivated Si(100) surfaces. The relative energies of PC 1-1, PC 2-1, PC 1-2, and PC 2-2 structures were 0.95, 1.33, 0.73, and 0.51 eV, respectively, below the reactant level, indicating that all the product structures could coexist on the initial surface. This was similar to the adsorption of TMG on the GaN surface reported by [PERSON] et al. in 2015 [32], with possible TMG adsorption models for low-temperature ALD proposed in their work. The Ga\({}_{2}\)(CH\({}_{3}\)) and Ga(CH\({}_{3}\))\({}_{2}\) species became new surface sites when TMG was adsorbed on the surface by consuming one- and two-adsorption site(s), respectively. The current work suggested that the ratio of each product structure involved in surface composition depends on the reaction barrier used to form them. Furthermore, the existence of Si\({}_{2}\)-NH species would support the adsorption of TMG at a low temperature as well as enhancing process reactivity due to the substantially lower activation barrier.