The properties of spark-processed material were studied by using photoluminescence and X-ray photo-electron spectroscopic measurements. The spark processing was performed in various N-O atmospheres. As a result of this processing, room-temperature radiative transitions occurred at 2.35eV and varied in intensity over 5 orders of magnitude; depending upon the N2/O2 ratio. After processing in pure N or pure O, however, the green photoluminescence disappeared and weak blue (2.7eV) or orange (1.9eV) photoluminescence bands, respectively, appeared. The temperature-dependent features of the 2.35eV emission were characterized by an intensity increase, together with a red-shift of the peak position at lower temperatures. The results of a cross-sectional study revealed that the green photoluminescence was generated mainly in a near-surface layer which had a chemical composition that was close to SiO2, and a N concentration that was below 1at%. Almost no photoluminescence was observed from a deeper SiO2 layer that was enriched with Si clusters and which had an increased N content (up to 7at%.). It was concluded that the results did not support a quantum-dot related photoluminescence mechanism for spark-processed Si. It was instead proposed that N additions reduced the densities of non-radiative centers which were introduced by Si dangling bonds.

M.H.Ludwig, A.Augustin, R.E.Hummel, T.Gross: Journal of Applied Physics, 1996, 80[9], 5318-24