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 HfO 2 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 HfO 2 dielectric was deposited on an InP substrate with an abrupt interface, the resulting HfO 2 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 -HfO 2 . The electronic structure and the charge-transition levels of t -HfO 2 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 -HfO 2 lead to substantial midgap states caused by interstitial elemental In or P in the t -HfO 2 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 HfO 2 using a thermal NH 3 treatment.