The properties of stain-etched porous material with 60 to 70% porosity were studied by using electron paramagnetic resonance, scanning tunnelling microscopic and Raman spectroscopic techniques. The samples contained 2 pore phases, with dimensions in the 1 and 10nm range, and exhibited both visible and infra-red photoluminescence. In the case of as-prepared and aged samples, 2 paramagnetic defects were detected. These were the Pb center at (111) Si/SiO2 interfaces, and the Si dangling bond center. The neutral Pb center concentration was of the order of 1018/cm3. This was an order of magnitude greater than that in comparable anodically etched porous Si. The angular variation of the Pb electron paramagnetic resonance spectrum demonstrated the mainly monocrystalline nature of the material. A neutral dangling bond concentration of less than 1017/cm3 indicated, in agreement with Raman data, that there was only a low (approximately 1%) fraction of disordered Si. The results demonstrated that highly luminescent porous Si, which retained the crystallinity of the substrate, could be prepared by stain etching.

M.Schoisswohl, J.L.Cantin, H.J.Von Bardeleben, G.Amato: Applied Physics Letters, 1995, 66[26], 3660-2