Elastic reflection of electrons by porous silicon layered ( PSL) surfaces: effects of porosity

The electrical and optical properties of porous silicon layers deposited on silicon substrates are determined by their electrochemical preparation conditions. Porous silicon layers (PSL) deposited on low resistivity (10m3 R cm) boron doped p+ Si exhibits channel structure, whereas layers formed on p type (l-3 n cm) Si wafers are sponge type. In the abundant literature on PSL, little attention was paid to their electron spectra. We presented in this paper, a study of p+ and p type PSL samples by elastic peak electron spectroscopy (EPES). The elastic reflection coefficient r&E, P) is strongly affected by physical parameters of the sample as the porosity, the substrate Si type as well the presence of H adatoms within the pores. r,(E, P) spectra are measured in absolute units (%) with a retarding field analyzer. A general tendency of spectra was the decrease of intensity with P (porosity) and E (primary electron energy). We have observed that HF treatment of the samples is producing a dramatic decrease of re,(E, P) in the low energy range (E = 50-150 eV). r&E, P) intensities were measured at E = 50, 100 and 150 eV. We observed that the excess reflection (coming from the pores sides) becomes important for porosity P > 0.6. A phenomenological model is presented based on the intact Si surface and reflection of electrons from the pores.