HYDROSTATIC-PRESSURE EFFECTS ON THE POROUS SILICON LUMINESCENCE

Recent high pressure measurements on different types of porous silicon (PS) samples have provided very interesting information on the variat ion and the stability of the related visible luminescence. It is shown that this luminescence still exists in samples which have undergone t he diamond-beta-Sn phase transition and persists in those samples when they are recovered at atmospheric pressure in the BC8 phase. Differen t techniques, including Raman and X-ray measurements, have been used t o determine the structure of the silicon on these luminescent samples. They provide upper bounds on the degree of the phase transformation w hich will be discussed. Since the results are not qualitatively depend ent on the way the samples are prepared, it is concluded that the obse rved effects are characteristic of the PS luminescence and that its ex istence cannot be related to the diamond phase of the silicon. Therefo re this luminescence is believed to originate more likely from the sur face of the silicon than from the bulk part.