The effect of implanting boron on the optical absorption and electron paramagnetic resonance spectra of silica

Abstract

Silica samples (type III, Corning 7940) were implanted with B using multiple energies to produce a layer ∼600 nm thick in which the concentration of B ranged from 0.034 to 2.04 at. %. Optical absorption spectra were measured from 1.8 to 6.5 eV. Electron paramagnetic resonance (EPR) measurements were generally made at ∼20.3 and 33 GHz for sample temperatures ranging from 77 to 100 K. Based on the EPR spectra three types of defects, namely, Eγ′, the E′-type 73 G split doublet (E73′), and the peroxyradical (POR) were identified. No oxygen-associated hole centers (OHCs) nor specific B-associated paramagnetic defects were detected, not even at the largest B concentration of 2.04 at. %. Unlike previous assignments, there was no correlation between the 4.83 eV optical absorption band and the observed PORs. From these results, we infer that in addition to POR, there is at least one additional Si-related state absorbing in the 4.8–4.9 eV range that is likely diamagnetic. The 5.85 eV optical absorption band is found to be due to the Eγ′ and E73′ centers, with, in average, quite similar oscillator strengths inferred as before. Both the optical absorption and the electron spin resonance data can be satisfactorily explained without the need for specific B-associated defect site (s). As no OHCs are detected by ESR, these do not seem to make a detectable contribution to the optical spectra.