Beryllium oxide(BeO)has a high dielectric constant(high-κ),low interface defect density and leakage current density.BeO also has excellent thermal stability in contact with Ⅲ-Vsubstrates.Thus,BeO is considered as the promising candidate for gate dielectric and interface passivation layer for future Ⅲ-VMOS devices.In addition,BeO is known to act as a strong diffusion barrier due to its very short Be-Obond and dense structure with small interstitial spaces as well as strong Be-Ocovalent bonding.The possible initial growth mechanism of BeO atomic layer deposition(ALD)on the hydroxylated GaAs surfaces using Be(CH3)2 and H2O precursors has been investigated by density functional theory(DFT).The ALD process is designed into two sequential half-reactions,i.e.,Be(CH3)2 and H2O half-reactions(Fig.1).Both of them proceed through an analogous trapping-mediated mechanism.By comparison of the reactions on Ga-rich GaAs surfaces with single and double hydroxyl sites,we find that the existence of neighboring hydroxyl can not facilitate the adsorption of Be(CH3)2 and lower the activation barrier obviously.In addition,our results indicate that the Be(CH3)2 half-reaction is thermodynamically more favorable as compared to the H2O half-reaction.In fact,Be(CH3)2 has been extensively used for the ALD of BeO films due to its relative high reactivity.Finally,we suggest that the reaction of the adsorbed-O-Be-CH3 group with its neighboring hydroxyl site is one preferential reaction pathway though it is energetically and kinetically less favorable than that with the H2O precursor.