Chemical states and electrical properties of a high-k metal oxide/silicon interface with oxygen-gettering titaniummetal-overlayer Appl.We present theoretical and experimental results regarding the thermodynamic stability of the high-k dielectrics ZrO 2 and HfO 2 in contact with Si and SiO 2 . The HfO 2 /Si interface is found to be stable with respect to formation of silicides whereas the ZrO 2 /Si interface is not. The metal-oxide/SiO 2 interface is marginally unstable with respect to formation of silicates. Cross-sectional transmission electron micrographs expose formation of nodules, identified as silicides, across the polycrystalline silicon/ZrO 2 /Si interfaces but not for the interfaces with HfO 2 . For both ZrO 2 and HfO 2 , the x-ray photoemission spectra illustrate formation of silicate-like compounds in the MO 2 /SiO 2 interface.
The atomic structure, stability and electronic properties of zirconium and hafnium nitrides and oxynitrides (MN, M3N4, and M2N2O; M=Zr, Hf) have been studied using first-principles density functional theory calculations. It is found that the orthorhombic Pnam structure of M3N4, which was observed experimentally for zirconium nitride, is more stable for this stoichiometry than the cubic spinel and rock-salt-type structures. The calculated band structures and electronic densities of states demonstrate that both the MN and M3N4 phases of zirconium and hafnium nitrides in the rock-salt-type structure are characterized by metallic properties, while the orthorhombic structure of the M3N4 phase exhibits an insulating behavior in agreement with experimental observations. The formation of nitrogen vacancies in the insulating M3N4 phase converts it into the metallic MN phase. Calculations of Zr2N2O and Hf2N2O in the cubic Bixbyite-type and hexagonal P3–ml crystal structures predict that these materials are insulators and that the Bixbyite-type structure found experimentally is lower in energy than the P3–ml phase.
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