STRUCTURE AND PROPERTIES OF POROUS SILICON OBTAINED BY PHOTOANODIZATION

The results of an investigation of layers of porous silicon (PS), whic h was obtained by electrochemical etching of p-Si under different illu mination conditions - natural light, incandescent light, and light fro m a mercury lamp with and without a filter - are reported. The structu re of the layers was studied by double-crystal x-ray diffractometry, t he composition was monitored by means of the m. absorption spectra, an d the radiative properties were monitored according to the photolumine scence (PL) spectra. It was established that electrochemical etching u nder illumination produces PS with a higher porosity and more intense PL whose maximum is shifted into the short-wavelength region, These ch anges are accompanied by a large disordering of the structure and an i ncrease in the oxygen content in the layer, It is concluded that illum ination accelerates the chemical interaction of PS with the electrolyt e due to oxidation. High-porosity porous silicon stored in air exhibit s quenching of PL. Conversely, PL is excited in layers with a lower po rosity. Aging of PS is characterized by an increase in the microdeform ation of the layers, a decrease in the crystallite sizes with a partia l loss of coherence between the crystallites and the substrate, and an increase in the fraction of the amorphous phase. (C) 1997 American In stitute of Physics. [S1063-7826(97)03010-X].