Time-resolved photoluminescence study of the red emission in nanoporous SiGe alloys

Porous Si1-xGex (PSiGe) layers with efficient room temperature visible photoluminescence (PL) were elaborated by anodical etching from p-type doped epitaxial layers with Ge contents from 5 to 30%. The luminescence is characterised by a broad PL band centred at 1.8 eV. Time resolved photoluminescence decay is studied in porous silicon germanium as a function of germanium content, temperature, emission energies and surface passivation. The PL decay line shape is well described by a stretched exponential in all cases. The effective lifetime at low temperature in as prepared porous Si1-xGex is 400 mu s, i.e. an order of magnitude less than in porous silicon. After the formation of a 20 Angstrom thick oxide surface layer we observe a decrease of the effective lifetime to 20 mu s at T = 4 K. (C) 1999 Published by Elsevier Science B.V. All rights reserved.