Defect states below the conduction band edge of HfO₂ grown on inp by atomic layer deposition

The electronic structure and nature of the defect states below the conduction band edge of an HfO₂ gate dielectric grown on InP substrate prepared by atomic layer deposition was examined using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and density functional theory (DFT). When the HfO₂ dielectric was deposited on an InP substrate with an abrupt interface, the resulting HfO₂ develops a tetragonal (t) structure, which minimizes the interfacial lattice mismatch. The O K-edge absorption features and DFT calculations indicated that additional structural distortion occurred by a q = -2 charged O vacancy (VO^-2) in the t-HfO₂. The electronic structure and the charge-transition levels of t-HfO₂ with VO^-2 were assigned based on a second derivative analysis of O K-edge features; 12 distinct pre-edge defect states below the Hf 5d conduction band edge were evident when the degeneracies resulting from Jahn-Teller splitting and crystal field splitting were removed. No changes in the electronic structure near valence band edge by VO^-2 were observed in XPS valence spectra. Moreover, O vacancies in t-HfO₂ lead to substantial midgap states caused by interstitial elemental In or P in the t-HfO₂ due to the enhanced out-diffusion of elemental In or P through O vacancies. We conclude that both the defect states near the CBE and the midgap states could be controlled by the incorporation of nitrogen into the HfO₂ using a thermal NH₃ treatment.