AVS 52nd International Symposium
    Electronic Materials and Processing Monday Sessions
       Session EM-MoM

Paper EM-MoM11
Differences in Band Edge Electronic Structure between Nanocrystalline ZrO@sub 2@ and HfO@sub 2@ Thin Films, and Bulk Crystals and Thin Films of Cubic Zironia (ZrO@sub 2@-Y@sub 2@O@sub 3@) and Hafnia (HfO@sub 2@-Y@sub 2@O@sub 3@)

Monday, October 31, 2005, 11:40 am, Room 309

Session: Electronic Properties of High-k Dielectrics and their Interfaces
Presenter: N.A. Stoute, North Carolina State University
Authors: N.A. Stoute, North Carolina State University
H. Seo, North Carolina State University
C.C. Fulton, North Carolina State University
D.E. Aspnes, North Carolina State University
G. Lucovsky, North Carolina State University
Correspondent: Click to Email
There is considerable interest in the band edge electronic structure of high-k oxides for applications as gate dielectrics in advanced semiconductor devices. This paper compares band edge electronic structure of nanocrystalline (nc) thin films of ZrO@sub 2@ and HfO@sub 2@, with i) bulk crystals of cubic zirconia and hafnia, e.g., ZrO@sub 2@ that is cubic as a result of incorporation of 5%-30% Y@sub 2@O@sub 3@, as well as ii) thin alloys of nanocrystalline ZrO@sub 2@-Y@sub 2@O@sub 3@ over a wider composition range. The band edge electronic structure of these alloy dielectrics has been studied by visible-near UV optical transmission and visible-near-UV-VUV spectroscopic ellipsometry. Band edge structure is also compared with ab initio calculations. For (Y@sub 2@O@sub 3@)@sub 0.095@(ZrO@sub 2@)@sub 0.905@ we observe a sub-bandgap absorption onset at ~4 eV, an absorption edge at ~5.3 eV and a weak d-state structure at ~6.3 eV. In contrast, nc-ZrO@sub 2@ has an absorption edge at ~5.7eV, and prominent d-state features at ~6.2 and 7.0 eV. Cubic (Y@sub 2@O@sub 3@)@sub 0.15@(HfO@sub 2@)@sub 0.85@ displays sub-bandgap absorption at ~ 4 eV, an absorption edge at ~5.9 eV, and a weak, broad d-state feature at ~7.5 eV, compared with an absorption edge at ~5.8 eV and sharp d-state features at ~6 and 7.2 eV in nc-HfO@sub 2@. The end-member ZrO@sub 2@ and HfO@sub 2@ nanocrystalline thin films display Jahn-Teller distortions that remove band edge d-state degeneracies that are not present in the Y@sub 2@O@sub 3@-stabilized cubic phases. The Y@sub 2@O@sub 3@-stabilized cubic phases display sub-bandgap absorption attributed to deep electronic states associated with the O-vacancies, while the nc-thin films display defects ~0.5 to 0.8 eV below the conduction band edge. These have been assigned to nanocrystalline grain boundary defects.