Raman scattering from free standing porous silicon under hydrostatic pressure

Luminescence and Raman scattering experiments have been performed on different types of porous silicon (PS) samples as a function of the 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 is still observed though the sample has been transformed in a structural phase different from the diamond phase. They provide also upper bounds on the degree of the phase transformation which is discussed. In addition specific PS Raman features are observed for the first time on these transformed samples. It is concluded that the PS luminescence is not related to the diamond phase of silicon and that the emitting medium involves more likely surface related complexes of the material.