EFFECT OF ELECTROCHEMICAL TREATMENTS ON THE PHOTOLUMINESCENCE FROM POROUS SILICON

In order to understand the mechanisms which limit the quantum efficiency of visible light emission from porous Si, the effects of electrochemical treatments on the luminescence intensity as well as the spectra have been studied in aqueous solutions. A strong improvement of the luminescence intensity has been noted in each step of the following sequential treatments in acid solution (0.1N H2SO4): (i) immersion into the electrolyte; (ii) anodic polarization; and (iii) desiccation. The only degradation of intensity has been observed in neutral solution (0.1M Na2SO4) following similar electrochemical treatments, although some recovery of the intensity has been noticed during anodic polarization. These photoelectronic behaviors, combined with our independent TEM observation of the porous Si, strongly suggest that the porous layer has a heterogeneous structure composed of a photo-absorptive, amorphous Si-like medium and Si clusters, dispersed in the medium, which act as emission centers.