STRUCTURE AND VISIBLE PHOTOLUMINESCENCE OF POROUS SI1-XGEX

Porous Si1-xGex layers with efficient room-temperature visible photoluminescence (PL) were elaborated by anodical etching from p- and p(+)-type doped epitaxial layers with Ge contents of 5% and 20%. The luminescence is characterized by a broad PL band centered at 650 Mn, similar to the case of porous Si; its width and spectral dependence vary only slightly with the Ge composition. Time-resolved PL spectra reveal lifetimes in the 10(2)-ns range decreasing with increasing Ge concentration. The pore structure of the p(+)-type layers has typical dimensions in the 50-100 Angstrom range and is [100] oriented. Electron paramagnetic resonance results show the presence of Si- and Ge-P-b centers as well as Si and Ge dangling-bond centers, the relative concentrations of which depend on the porosity and the surface passivation state. The angular variation of the Si- and Ge-P-b center electron paramagnetic resonance spectra demonstrate the crystallinity of the porous SiGe layers.