Porous layers with efficient room-temperature visible photoluminescence properties were prepared by the anodic etching of p-doped and p+-doped epitaxial layers with Ge contents of 5 or 20%. The luminescence was characterized by a broad photoluminescence band that was centered at 650nm; similar to the case of porous Si. Its width and spectral dependence varied only slightly with Ge composition. Time-resolved photoluminescence spectra revealed lifetimes, in the 100ns range, which decreased with increasing Ge concentration. The pore structure of the p+-type layers typically had dimensions of 5 to 10nm, and was [100]-oriented. Electron paramagnetic resonance results revealed the presence of Si- and Ge-Pb centers as well as Si and Ge dangling-bond centers. Their relative concentrations depended upon the porosity and the surface passivation state. The angular variations in the Si- and Ge-Pb center electron paramagnetic resonance spectra demonstrated the crystallinity of the porous SiGe layers.

M.Schoisswohl, J.L.Cantin, M.Chamarro, H.J.Von Bardeleben, T.Morgenstern, E.Bugiel, W.Kissinger, R.C.Andreu: Physical Review B, 1995, 52[16], 11898-903