We applied photoacoustic (PA), photoluminescence (PL), photoluminescence excitation (PLE), and atomic force microscopy (AFM) techniques on porous silicon (PS) layers to study the influence of chemical etching by low-concentration hydrofluoric acid. The chemical etching reveals the formation of PS layers of small dimensions by AFM observations, indicating the possibility of a strong quantum confinement effect. PA spectroscopy is useful to obtain the optical absorption characteristic for strongly scattering media such as PS and it helps to confirm the above speculation by indicating the blueshift of the fundamental absorption edge for the PS layer with chemical etching. PL spectroscopy also confirms the possibility of a quantum confinement effect by revealing the strong intensity and blueshift for the PS layer with chemical etching. PLE measurements suggest that the site for the radiative processes is different from that for the recombination of carriers and the PL of PS layers were dominated only by small ...

Photoacoustic and photoluminescence studies of porous silicon etched by low-concentration hydrofluoric acid

Photothermal spectroscopy experiments have been used for the first time to study non-radiative processes in mesoporous silicon layers of varying porosity. Data on low porosity material can be explained by a model which involves interference between thermal waves reflected at the porous silicon film-silicon substrate interface. High porosity material, which exhibits strong red photoluminescence, cannot be fitted to this model. These materials seem to indicate the existence of another critically damped wave-like excitation in addition to the thermal waves.

R Williams

Papers

Photothermal spectroscopy of mesoporous layers on heavily doped n-type silicon substrates