SPATIALLY RESOLVED RAMAN MEASUREMENTS AT ELECTROLUMINESCENT POROUS N-SILICON

The cross section of electroluminescent (EL) porous silicon layers (LEPOS) made from n- and p-doped silicon has been investigated by means of micro-Raman and photoluminescence (PL) spectroscopy to find the luminescence active zone in LEPOS. Special care has been taken to avoid the heating of the sample. Additionally an energy dispersive spectroscopy scan over the sample cross section has been performed for n-LEPOS to detect the distribution of oxygen. Since the n samples display much better EL properties than the p samples, the investigations concentrate on the n samples. For n-LEPOS, a layered structure has been found with SiOx/Si at the top followed by a PL active layer. There are two types of samples showing different forms of Raman spectra. Type-I spectra are narrow and shifted by small values as compared with the Raman spectra of bulk silicon. They have a shoulder at about 510 cm-1 only in the PL active layer. Type-II spectra are broad and shifted by about 7-10 cm-1. All the electroluminescent samples show Raman spectra of type I.