Electron Paramagnetic Resonance Studies of HF-CVD Diamond Films
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ABSTRACT Diamond thin films have been deposited on silicon substrates by hot-filament chemical vapor deposition (HF-CVD). Substrate temperature and methane concentration have been varied and the resulting structural properties of the deposited films studied. Raman spectroscopy, scanning electron microscopy and electron paramagnetic resonance (EPR) measurements were performed. The EPR measurements showed a single spectrum at g = 2.002"7(2). The bulk concentration of the paramagnetic species, as determined from the total EPR absorption were found to vary in the range 1017 to 1019 cm-3 . Low paramagnetic defect concentrations were found for samples exhibiting a low non-diamond carbon contribution to the Raman spectrum. These samples were those grown with a methane concentration of I % or less.
INTRODUCTION The growth of diamond at low temperatures and pressures by chemical vapor deposition has now developed so that films of high quality, as characterized by Raman spectroscopy, can be routinely fabricated. Extensive studies have been made on diamond films using various characterization techniques. The technological important thermal[1,2] and electrical properties[3,4] of these films are dependent on the incorporation of point and extended defects and non-diamond phases. An approximate relation has been shown between the Raman full width at half maximum (FWHM) and the electrical properties, and has been attributed to differences in the defect density[3]. Electron paramagnetic resonance (EPR) spectroscopy has high sensitivity to paramagnetic charge states of point defects in carbon phases. A number of EPR studies on diamond films have been reported[5-10], but a complete understanding of the origin of the paramagnetic defects observed has yet to be achieved. 501 Mat. Res. Soc. Symp. Proc. Vol. 423 0 1996 Materials Research Society
Previous studies[5-10] have reported the observation of an intense EPR spectrum from asgrown diamond films. The reported g-values range from 2.0021 to 2.0028. Variations in lineshape and linewidth have also been observed. Typically the spectrum exhibits partially resolved structure. Jia et. al.[8] have studied the EPR spectra from diamond thin films grown with gas mixtures H2 /CH 4 , D2/CH 4 and H 2/ 13 CH 4 from which they were able to conclude that the dominant contribution to the spectrum involved a paramagnetic center localized on a carbon site. The satellite lines were assigned to an interaction with hydrogen nuclei. In a 9.5 and 35 GHz EPR study of diamond films Holder et.al.[7] observed that the satellite lines were at - ±gNPfNBo with respect to the central line showing that they could not be due to hyperfine interaction but likely resulted from weak magnetic dipole coupling between the electronic spin and neighboring hydrogen nuclei[ 11] and were so called 'spin-flip' satellites. Earlier cross-polarization (CP) combined dynamic nuclear polarization (DNP) magic angle spinning (MAS) experiments[ 12] on diamond films had detected proton polarization transferred to the 13 C spin-system of
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