The physical and electrical effects caused by interfacial reactions of HfO2 on Si-passivated GaAs were investigated by various methods. The results showed that the Si layer decreases the diffusion and formation of Ga-O. Moreover, post-nitridation in HfO2/Si/GaAs significantly reduced the formation of As-O and Ga-O. The depth profiling data showed that two separated layered structures were formed with HfO2 and a mixture of HfO2 and SiO2 after the annealing process. The crystalline structure and formation of Ga-O in the film affect the band offsets between GaAs and the high-k HfO2 dielectric. Moreover, the Si passivation effectively suppressed the interfacial defects caused by Ga-O diffusion during the annealing treatment. The nitridation cause As diffusion to oxygen vacancy of HfO2 result in the increase of the interfacial defect. (c) 2013 Elsevier B.V. All rights reserved.