FORMATION OF LUMINESCENT CHEMICALLY ETCHED POROUS SILICON

We report a systematic study on the formation of photoluminescent chem ically etched porous silicon. Samples have been fabricated in HF/HNO3 based solutions for various etching times. The growth of the luminesce nt layer has been studied by correlating film porosity, thickness and integrated photoluminescence intensity to the etching time. For long e tching duration porosity attains an almost constant value while the ra te of film formation strongly decreases. On the other hand Photolumine scence spectra, recorded in the visible range, are similar in shape fo r the various samples. Our data are explained assuming the existence o f a critical pore width, W-c, such that, once initiated, the preferent ial etching at some anodic site on the silicon surface stops only when W-c is reached.