AVS 53rd International Symposium
    Electronic Materials and Processing Thursday Sessions
       Session EM+AS-ThM

Paper EM+AS-ThM6
A Soft-X-Ray Photoelectron Spectroscopy Study of D-State Contributions to Valence Band States in Nanocrystalline HfO2, TiO2, and Hf1-xTixO2 Alloys

Thursday, November 16, 2006, 9:40 am, Room 2003

Session: High-k Dielectric Characterization
Presenter: L.B. Fleming, NC State University
Authors: L.B. Fleming, NC State University
M.D. Ulrich, NC State University
J. Rowe, University of North Carolina at Chapel Hill
C.C. Fulton, NC State University
G. Lucovsky, NC State University
Correspondent: Click to Email
This paper compares d-state contributions to valence band, and valence band edge defect states determined from i) synchrotron soft x-ray photoelectron spectroscopy (SXPS) at photon energies between 40 and 80 eV, with d-state contributions determined from ii) ultra-violet photoemission spectroscopy (UPS) at 21.2 eV. Measurements have been performed on thin films of HfO@sub 2@, TiO@sub 2@ and Hf@sub 1-x@Ti@sub x@O@sub 2@ alloys prepared by reactive evaporation, and subjected to post deposition annealing at 700°C. The atomic Hf, Ti and O contributions to the valence band states in the SXPS and UPS spectra are at approximately the same energies with respect to the Fermi level, but have different spectral weighting. The only significant differences in the USP and SXPS spectra are defect state features at, and above the valence band edge. The UPS spectra, limited by the incident photon energy, yield a single feature with a spectral peak ~1 eV above the valence edge, whereas SXPS spectra, performed with higher incident photon energies can defect electronic states deeper into the forbidden band gap. The SXPS spectra confirm the band edge features, as well as identifying a second defect states at higher energy, ~3 eV above the valence band edge. The defect states in TiO@sub 2@, and the alloys are interpreted in as O-atom vacancy states in which the formal valence of Ti is 3+ rather than 4+. This assignment is based on comparisons between SXPS spectra, and epsilon 2 spectra obtained from analysis of reflection spectra of Ti@sub 2@O@sub 3@ over a spectra range from 0.01 eV to 10 eV. Defect states in HfO@sub 2@ are similar, and assigned to d-states of Hf@super 3+@ at O-atom vacancies.