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Non-crystalline SiO2: processing induced pre-existing defects associated with vacated O-atom intrinsic bonding sites

G. LUCOVSKY1,* , J. W KIM1, K. WU1, D. ZELLER1, B. PAPAS1, J. L. WHITTEN1

Affiliation

  1. North Carolina State University Raleigh, N.C., 27695-8202, USA

Abstract

Electron spin resonance (ESR) studies by Galeener and co-workers on bulk-quenched silica (SiO2) have distinguished between pre-existing, and X-ray and γ-ray radiation induced defects. Pre-existing defect densities increase exponentially with increasing quenching and annealing temperatures and in “dry silicas” these are assigned to X-ray activated E’ centers, singly occupied Si atom dangling bonds. Non-bonding O hole centers, NBOHC defects are also detected in dry silicas, but only after X-ray or γ-ray irradiation, and these defects increase linearly with the radiation dosage. Pre-existing defects have also been detected by 2nd derivative O K pre-edge X-ray absorption spectroscopy in remote plasma deposited and thermally grown SiO2 and GeO2 thin films. These spectra display singlet and triplet features labeled according to Tanabe-Sugano diagrams. It is demonstrated by ab initio theory and experiment that pre-existing defects in thin film SiO2 and GeO2 are vacated O-atom sites in which an O atom has never resided, rather than O-vacancy sites from which an O-atom bond has been broken and remains within the material. As such Tanabe-Sugano diagram symmetries and singlet and triplet labeling have been extended to d-states on nearest-neighbor Si and Ge dangling bonds in these vacated sites. Vacating Oatoms complement chemical bonding self-organizations that result in medium range order (MRO) as an additional mechanism providing local strain relief. Based on ESR, pre-existing defects (i) in As1-xS(Se)x alloys, including As2S(Se)3, and (ii) in S(Se)-rich Ge1-xS(Se)x alloys are qualitatively different that pre-existing defects in (i) SiO2 and GeO2, and (ii) GeS(Se)2. These differences are associated with fundamental differences in their respective electronic structures..

Keywords

SiO2, Defects, Oxygen sites.

Submitted at: Nov. 1, 2011
Accepted at: Nov. 23, 2011

Citation

G. LUCOVSKY, J. W KIM, K. WU, D. ZELLER, B. PAPAS, J. L. WHITTEN, Non-crystalline SiO2: processing induced pre-existing defects associated with vacated O-atom intrinsic bonding sites, Journal of Optoelectronics and Advanced Materials Vol. 13, Iss. 11-12, pp. 1359-1363 (2011)