Abstract
Strong light emission has been observed in porous silicon layers prepared by immersing highly doped silicon wafers in a HF/HNO3/H2O etching solution. Morphological information has been obtained through porosity measurements, scanning electron microscopy (SEM), scanning tunnelling microscopy (STM) and Raman spectroscopy. The material optical properties have been investigated by photoluminescence (PL) and photoacoustic (PAS) spectroscopies. The image obtained shows that in chemically prepared porous silicon (CPS), three phases, namely, macroporous, mesoporous and microporous, exist. SiOx, c-Si, and voids are suggested to affect the optical response of the layers. Comparisons of PL spectra of CPS and electrochemically prepared PS (EPS) samples with the same and higher porosity values reveal marked similarities, suggesting that carrier confinement in nanometer-sized structures plays a key role in the light-emission process.