Luminescence and Raman scattering from porous silicon under high hydrostatic pressure: an evidence for the surface related mechanisms of luminescence

Luminescence and Raman scattering experiments have been performed on different types of porous silicon (PS) samples as a function of hydrostatic pressure. These measurements allow to compare the response of the material in different structural phases, and show that under moderate conditions of pressurization the strong PS luminescence still exists in samples which have undergone the diamond to β-Sn phase transition, and persists in those samples when they are recovered at atmospheric pressure in the BC8 phase. This intense PS luminescence intensity collapses by about two orders of magnitude for pressures beyond 17 GPa, value coinciding with that of the second high pressure phase transition β-Sn to simple hexagonal. They provide also upper bounds on the relative quantity of nanosize crystallites eventually present in these PS samples. In addition specific PS Raman features are observed on these transformed samples. It is concluded that the PS luminescence is very likely not related to the diamond phase of silicon and therefore originates more likely from surface related complexes of the material. (orig.)