Optical detection of microwave-induced impact ionization of bound excitons in silicon

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Abstract
In this paper we present the first experimental evidence for the cause of the nonresonant background signals commonly observed in optically detected magnetic resonance (ODMR) experiments in silicon. By making a direct comparison of bound-exciton (BE) photoluminescence (PL) intensity changes in an electric field with microwave-field-induced similar PL changes in n-type Si, we show that the main physical mechanism causing the ODMR background signal at lower microwave frequencies is impact ionization of free and bound excitons. We show that the efficiency of the microwave-induced impact ionization of bound excitons (BE’s) is very strong, and it causes complete quenching of PL intensity for BE’s associated with shallow donors. As a result the PL intensity can be enhanced by more than 150% for isoelectronic BE’s. The change in PL intensity with microwave power shows a characteristic threshold, which was typically 20 mW at 9 GHz microwave frequency in our case.