Infrared modulation of photoluminescence in glow discharge amorphous silicon

Dual beam photoluminescence (PL) from a-Si:H was measured at various temperatures by exciting the sample with a modulated infrared (IR) beam in addition to a steady beam of visible light. Varying the modulation frequency revealed that the IR caused a transient enhancement of the PL, followed by a slow quenching effect. The IR excitation spectrum showed quenching by photons with energies between 0.45 and 1.1 eV, similar to the IR quenching of photoconductivity. The fast process enhanced the emission peak equally at all energies, while the slow process quenched only the high energy side of the peak. These results can be explained by the re-excitation of holes from ``safe traps'' by the IR, followed by recombination at dangling bonds.