In contrast, ALD of GaN from TEG has been less studied. Stegmuller et al, have presented a quantum chemical study on the gas-phase decomposition pathways of TEG using density functional theory (DFT). They concluded that β-hydride elimination, i.e., replacing one ethyl ligand with a hydrogen on the gallium center while forming ethylene, is the dominant gasphase decomposition pathway for TEG in a thermal CVD process. In surface chemistry studies with TEG, ethyl groups are found to deposit onto the surface by the decomposition of TEG, followed by desorption at higher temperatures as ethylene (C2H4) and/or ethane (C2H6). This reaction has been shown on Ni(100) , GaAs(100) and Si(100) . For ALD of GaN, TEG adsorption and subsequent reactions are dependent on the surface termination after the NH3 pulse. We have previously investigated equilibrium surface terminations after the NH3 pulse on GaN(0001) and shown that -NH2 was the main surface structure up to about 600K. In a previous study on ALD of GaN using TEG and NH3 with and without plasma activation of ammonia, we explored how the surface chemistry can enhance the elimination of the ethyl ligands by introducing a reactive B pulse of H2, Ar plasma, or H2-Ar plasma, between the TEG and ammonia pulses. The results showed that adding a B-pulse afforded higher growth per cycle (GPC). We hypothesized that H2 gas as a B pulse would favor H2-assisted C2H6 elimination, Ar plasma would bring additional energy to the surface, favoring β-hydrogen elimination, while H2-Ar-plasma as B pulse would favor both H2-assisted C2H6 elimination and β-hydrogen elimination of C2H4. All these mechanisms would render a hydrogen-terminated surface with less steric hindrance than an ethyl-terminated surface.