Defect states in epitaxial HfO2 films induced by atomic transport from n-GaAs (100) substrate

Abstract

We investigated the chemical states and nature of the defect states below the conduction band edge of HfO2 films grown on GaAs (100) substrates using high-resolution x-ray photoelectron spectroscopy (HRXPS), x-ray absorption spectroscopy (XAS), and density functional theory calculations. O K1-edge absorption spectra of the HfO2/GaAs film revealed two distinct conduction band edge defect states, located at 1.6 ± 0.2 eV and 3.0 ± 0.2 eV below the conduction band edge in HfO2. The combined XAS and HRXPS results as a function of post-deposition annealing temperature indicated that the changes in defect states below the conduction band edge of HfO2 were correlated with the extent of interfacial chemical reactions between the HfO2 film and the GaAs substrate. Spectroscopic and theoretical results revealed that the two conduction band defect states are caused by (i) diffused Ga–O states, Hf3+ states, and (ii) an O divacancy related to the As–O states, respectively.