DEFECTS AND VISIBLE PHOTOLUMINESCENCE IN POROUS SI1-XGEX

We prepared porous SiGe layers by anodic etching from epitaxial SiGe l ayers of 5 and 20% Ge content and of two different doping concentratio ns (p, p(+)). Their morphology was investigated by electron microscopy and electron paramagnetic resonance. The structural analysis reveals for the p and pf material a pore structure very similar to the case of porous Si. The electron paramagnetic resonance measurements show for the high porosity SiGe layers after 300 degrees C oxidation the presen ce of Si-Pb centres, which proves the monocrystalline character of the porous layers. In addition Ge dangling bond defects are observed; the y are ascribed to Ge precipitates at the oxide interface. The SiGe lay ers with a porosity higher than 60% show efficient red room-temperatur e photoluminescence (PL). The maximum of the pi, is centred at 1.8 eV with a half width of about 0.4 eV, Time resolved PL spectra reveal lif etimes for this red PL in the 100 ns range, decreasing with increasing Ge concentration.