Determination of the phase composition of surface layers of porous silicon by ultrasoft X-ray spectroscopy and X-ray photoelectron spectroscopy techniques

The phase composition of the surface layers in porous silicon (por-Si) is determined by analysis of the density of states in the valence band using ultrasoft X-ray emission spectroscopy (USXES) and X-ray photoelectron spectroscopy (XPS) of the core levels. Since porous silicon demonstrates instability of its properties the investigations of the changes in its phase composition under atmosphere exposure (e.g. low-temperature anneals in an oxygen flow) have been made. Phase analysis by USXES is performed with the help of a specially elaborated mathematical technique using expansion of the experimental spectrum by the spectra of some standard samples, c-Si and c-SiO2 as well as disordered phases of these species (by USXES) and low-oxidized defect silicon (by USXES and XPS) have been detected in the surface layers of per-Si. Some changes in the composition were found in the samples annealed in oxygen at various temperatures. (C) 2001 Elsevier Science B.V. All rights reserved.