PHOTOLUMINESCENCE PEAK ENERGY EVOLUTION FOR POROUS SILICON DURING PHOTOOXIDATION AND GAMMA-RAY OXIDATION

The evolution of photoluminescence (PL) from a series of as-anodized porous silicon (PS) samples with peaks in a wide energy range has been investigated systematically during oxidation enhanced by either laser illumination or gamma-ray irradiation. Under both oxidation conditions, PL spectra initially located in the infrared-red region undergo a blue shift, while those initially located in the orange-yellow region experience a red shift. Eventually, all the peaks are pinned at fixed energies which are in an energy range narrower than that for as-anodized PS samples. These experimental results can be explained by the quantum confinement-luminescence centres model, which argues that photoexcitation proceeds in nanoscale silicon and photoemission through the luminescence centres outside nanoscale silicon, and also by assuming that during oxidation the main luminescence centres change from one kind to another and/or the relative contributions to the PL intensity from various kinds of luminescence centres vary.