Jpn. J. Appl. Phys. 46 (2007) pp. 1899-1909  |Previous Article| |Next Article|  |Table of Contents|
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Intrinsic Electronically Active Defects in Transition Metal Elemental Oxides

Gerald Lucovsky, Hyungtak Seo, Sanghyun Lee, Leslie B. Fleming, Marc D. Ulrich, Jan Lüning¹, Pat Lysaght², and Gennadi Bersuker²

(Received September 15, 2006; accepted December 23, 2006; published online April 24, 2007)

Densities of interfacial and bulk defects in high-κ dielectrics are typically about two orders of magnitude larger than those in Si–SiO₂ devices. An asymmetry in electron and hole trapping kinetics, first detected in test capacitor devices with nanocrystalline ZrO₂ and HfO₂ dielectrics, is a significant potential limitation for Si device operation and reliability in complementary metal oxide semiconductor applications. There are two crucial issues: i) are the electron and hole traps intrinsic defects, or are they associated with processed-introduced impurities?, and ii) what are the local atomic bonding arrangements and electronic state energies of these traps? In this study, thin film nanocrystalline high-κ gate dielectrics, TiO₂, ZrO₂, and HfO₂ (group IVB TM oxides), are investigated spectroscopically to identify the intrinsic electronic structures of valence and conduction band states, as well as those of intrinsic bonding defects. A quantitative/qualitative distinction is made between crystal field and Jahn–Teller (J–T) d-state energy differences in nanocrystralline TM elemental oxides, and noncrystalline TM silicates and Si oxynitrides. It is experimentally shown and theoretically supported that a length scale for nanocrystallite size <2–3 nm i) eliminates J–T d-state term splittings in band edge π-bonded d-states, and ii) represents a transition from the observation of discrete band edge defects to band-tail defects. Additionally, π-state bonding coherence can also be disrupted with similar effects on band edge and defect states in HfO₂ films which have been annealed in NH₃ at 700 °C, and display Hf–N bonds in N atom K₁ edge X-ray absorption spectra.

URL: http://jjap.jsap.jp/link?JJAP/46/1899/
DOI: 10.1143/JJAP.46.1899
KEYWORDS:transition metal oxides, crystal field and Jahn–Teller d-state splittings, ab initio molecular orbital theory, valence and conduction band states, intrinsic defect states, coherent π-bonding interactions, nanocrystalline length scales of order

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