Electron structure of porous silicon obtained without the use of HF acid

Porous silicon is an utterly unique material. Since 1990 when Canhem revealed visible photo-luminescence in por-Si [1], the number of publications concerned with technology of its producing, the study of its properties as well as its real and possible applications in various fields of science and industry continuously grows. Fabrication of porous silicon is based on the etching (chemical or electrochemical) of the wafers of single- or poly-crystalline Si. Fluoric acid (HF) is applied as one of the main components in solutions for etching. However, this acid is a potent substance and is really dangerous for the human health and can be hazardous for the environ-ment. Therefore, we have tested and improved an alternative technique for electrochemical etching of silicon [2, 3], where the concentrated aqueous solution of ammonium fluoride NH4F is used instead of HF. Since mobility of NH ions in aqueous solution is much less than that one for hy-drogen ions if HF solution is used as an etchant then sili-con is etched at a less rate. Therefore, a strong oxidant must be added to the solution, in our case it was nitric acid. The aim of this work was the study of the properties of por-Si obtained with the use of this new improved tech-nique of etching. For the analysis we applied the following experimental techniques: scanning electron microscopy (SEM), ultrasoft X-ray emission spectroscopy (USXES), X-ray absorption spectroscopy near absorption edge (XANES) and X-ray photoelectron spectroscopy of the core levels. Moreover, basing on the elaborated computer program [4] an estimation of the phase composition for the near-surface layers of obtained por-Si was performed.