X-ray absorption spectroscopy (XAS) is used to study band edge electronic structure of high-k transition metal (TM) and trivalent lanthanide rare earth (RE) oxide dielectrics. The lowest conduction band d*-states in nano-crystalline TiO 2, ZrO 2 and HfO 2 are correlated with features in the O K 1 edge, and transitions from occupied Ti 2p, Zr 3p and Hf 4p states to empty Ti 3d-, Zr 4d-, and Hf 5d-states, respectively. Optical band gaps, E opt , and conduction band offset energy with respect to Si , E B , scale monotonically with d-state energies of the TM/RE atoms. The multiplicity of d-state features in the Ti L 2,3 spectrum of TiO 2, and the O K 1 derivative spectra for ZrO 2 and HfO 2 indicate a complete removal of d-state degeneracies resulting from a static Jahn-Teller effect. Similar degeneracy removals are shown for complex nano-crystalline TM/RE oxides such as Zr and Hf titanates, and La , Gd and Dy scandates. XAS and band edge spectra indicate an additional band edge defect state assigned Jahn-Teller distortions at internal grain boundaries. These defect states are electronically active act as bulk traps in metal oxide semiconductor (MOS) devices, contributing to asymmetries in tunneling and Frenkel-Poole transport with important consequences for performance and reliability in advanced Si devices.
Conduction band-edge States associated with the removal of d-state degeneracies by the Jahn-Teller effect
