ELECTRON-SPECTROSCOPY OF POROUS SILICON LAYERS INDIRECT DETECTION OF HYDROGEN BY ELASTIC PEAK ELECTRON-SPECTROSCOPY

Efficient visible luminescence from porous Si (PSi) layers is associated with the quantum size and the presence of hydrogen as a passivaant on the inner surface. The increase of the amount of H was performed by wet chemical etching in HF, producing the increase of photoluminescence intensity. The detection of H is not possible by AES or XPS and is difficult even with EELS. Elastic peak electron spectroscopy (EPES) showed a large decrease of the elastic reflection coefficient r(e) appearing in the elastic peak, and measured with a retarding field analyser (RFA). The effective elastic backscattering coefficients of a monolayer of H, Si, O were calculated for the RFA angular window and resulted in reasonable agreement with literature data available. They were completed for the 50-100 eV range. Experiments on a Si(111) wafer verified calculations. A dramatic decrease of r(e) was found on HF-etched PSI (a factor of 3-10) in the 50-100 eV range. Above 200 eV, effects are shadowed by the contribution of deeper layers of the substrate and reduced attenuation of the H adlayer. This indicates the formation of high H coverage on the porous inner surface. Experiments are interpreted by multiple elastic reflection and attenuation of electrons by the H-covered porous surface. Detailed AES and EELS studies made with a hemispherical analyser resulted in Si and SiO2 bond on the surface.