Intrinsic limitations for CMOS with high-k gate dielectrics: electrically-active grain boundary and oxygen atom defect states

Chemically pure thin films of HfO₂, as well as other transition metal (TM) and rare earth (RE) elemental and complex oxides, e.g., LaScO₃ and LaAlO₃, are nanocrystalline as-deposited. The local bonding environments of TM and RE atoms are distorted with respect to ideal octahedral or cubic bonding, and degeneracies of the respective band edge d-states are completely removed by Jahn-Teller (J-T) distortions. Spectroscopic studies have revealed J-T term splittings, and additionally two localized states. The first is associated with an electronically-active defect at the nanocrystalline grain boundaries and the second with O-atom vacancies. These states are different energies within the band gaps of HfO₂ and ZrO₂.