Evidence for fast decay dynamics of the photoluminescence from Ge nanocrystals embedded in SiO2

We have investigated the origin of room temperature photoluminescence from ion-beam synthesized Ge nanocrystals (NCs) embedded in SiO2 using steady state and time-resolved photoluminescence (PL) measurements. Ge NCs of diameter 4-13 nm were grown embedded in a thermally grown SiO2 layer by Ge+ ion implantation and subsequent annealing. Steady state PL spectra show a peak at similar to 2.1 eV originating from Ge NCs and another peak at similar to 2.3 eV arising from ion-beam induced defects in the SiO2 matrix. Time-resolved PL studies reveal double exponential decay dynamics on the nanoseconds time scale. The faster component of the decay with a time constant tau(1) similar to 3.1 ns is attributed to the nonradiative lifetime, since the time constant reduces with increasing defect density. The slower component with time constant tau(2) similar to 10 ns is attributed to radiative recombination at the Ge NCs. Our results are in close agreement with the theoretically predicted radiative lifetime for small Ge NCs. (C) 2004 Elsevier Ltd. All rights reserved.