Afterglow effect in photoluminescence of Si:Er

The afterglow effect of slowly decaying photoluminescence, well known for phosphor materials, is identified in silicon. A component with a lifetime of up to 100 ms is observed in kinetics of the λ≈1.5 μm emission of Er-doped crystalline silicon. This is measured at T≈4.2--40 K under pulsed band-to-band excitation with a Nd:YAG laser (532 nm). The slow component is found to be superimposed upon the Er-related emission characterized by the commonly reported lifetime of approximately 1 ms. Thermalization and subsequent recombination of nonequilibrium carriers trapped at shallow levels after the excitation pulse is proposed as the microscopic mechanism responsible for this slow emission. Using time-resolved two-color spectroscopy with a free-electron laser, the earlier reported mid-infrared induced enhancement of Er emission is related to the presently observed afterglow. A simple kinetic model is developed and shown to successfully link the amplitude and temporal characteristics of both effects. Measurements at higher temperatures support the proposed interpretation.