Luminescence and Raman scattering from porous silicon under high hydrostatic pressure: A test for the present models 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 one 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 beta-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. The Raman lineshape analysis provides upper bounds for the relative quantity of nanosize crystalites 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, originating therefore from surface-related complexes.