Effects of B and N implantation on optical absorption and photoluminescence and comparison to the effects of implanting Si, Ge, O, and Ar in silica

Abstract

Silica samples were implanted at multiple energies with B and N ions, which resulted in a constant concentration implanted layer ∼600 nm thick starting ∼100 nm below the sample surface. The energies to produce the constant concentration layer ranged from 35 to 320 keV and the concentrations were 0.03–2.1 at.% for B and 0.024–2.5% for N. The optical absorption of the suite of samples was measured from 2.8 to 6.5 eV. No bands were detected at energies <2.8 eV. Bands which have been identified in the literature as intrinsic to SiO 2 were fitted to the data with only one free parameter, the amplitudes of the maxima of the bands. This fit was within ±2% from 2.8 to 5.4 eV. To fit the data from 5.4 to 6.6 eV we assumed that there was a single band with an energy >6.5 eV. The nonlinear fitting program calculated a band at 6.76 ± 0.06 eV with a width at half maximum amplitude of 0.81 ± 0.08 eV, for all concentrations of B and a band at 6.65 ± 0.06 eV with a full width at half maximum of 0.67 ± 0.08 eV for the N implanted samples to achieve a fit to ±2% from 5.4 to 6.5 eV. In the range of energies from 2.0 to 6.5 eV no bands attributable to either B or N were required to fit the observed optical absorption. Excitation of the samples with 5 eV photons produced a photoluminescence [PL] band at 4.43 ± 0.02 eV with a full width at half maximum amplitude [FWHM] of 0.53 ± 0.02 eV. When measured at 4.43 eV the photoluminescence excitation [PLE] band had a maximum at 5.00 ± 0.02 eV with a FWHM of 0.40 ± 0.02 eV. Bands with approximately the same energies and FWHMs were observed in the N samples as observed in the B samples. The correlation of the amplitudes of these PL bands with the amplitudes of the absorption bands at 5.01 and 5.17 eV is less than one. Based on a comparison of the absorption amplitudes deduced from the linear and nonlinear fitting procedure, and PL and PLE amplitudes in the B, Si, N, O, and Ar samples, an absorption band at 5.00 ± 0.02 eV producing the PL at 4.43 ± 0.02 eV is due to a Si related defect state. In the Ge case PL bands were observed at 4.38 ± 0.02 and 3.23 ± 0.02 eV with PLE bands at 4.98 ± 0.2 and 5.18 ± 0.02 eV, respectively. An absorption band at 5.17 eV is the source of the 3.23 eV PL band and is, therefore Ge related. The fitted absorption spectra in the Ge case required another absorption band at 5.54 ± 0.07 eV as well as a band at 6.87 ± 0.04 eV to fit the spectra in the Ge case for all concentrations, to within the ±2%. PL bands at other energies were not detected in the PL spectra of any of the samples when excited with energies in the 4.5–6.4 eV range.