Nanoscale Res Lett (2006) 1:11–19 17 Fig. 10 Temperature dependence of PL spectra from Ge nanoclusters on Si(100) grown with a BLAG method. The nominal Ge thickness is 0.5 ML and Xe buffer thickness is 6 ML attribute our observed sublinear power exponent to a competition of a localized radiative recombination processes against parallel Auger recombination chan- nels. Figure 10 shows the dependence of the PL spectra on measurement temperature for band P1 and P2. The integrated PL intensity and the peak positions as a function of measurement temperature for band P1 and P2 are shown in Fig. 11a and b, respectively. The PL intensity starts to decrease rapidly at 75 K for both bands. The thermal activation energy EA can be ob- tained from the Arrhenius plot of the PL intensity. The deduced EA is 18.6 meV for P1 and 11.2 meV for P2. The obtained EA would correspond to the energy for the excitons escaping from the radiative centers to non- radiative recombination centers. The low activation energy means a weak conﬁnement and explains a quick PL intensity decrease. Fig. 12 PL spectra obtained for single layer Ge cluster structures grown using BLAG process. Schematics of the examined samples are shown at the left of the corresponding PL spectra. Only the peak ratios change as a function of layer number indicating that every layer has the same purity. The intensities are in arbitrary units and the energy scale is in eV The peak energies of the P1 and P2 bands red-shift with temperature, however, the variations depart sig- niﬁcantly from the Varshni relationships of the Ge bandgap and the Si bandgap [24]. This result again conﬁrms that the P1 and P2 transitions are not asso- ciated with the Ge band edges or Si band edges, indi- cating a ‘‘bound to bound’’ nature of the P1 and P2 transitions. These localized luminescence centers Fig. 11 The temperature dependence of PL spectra from Ge nanoclusters with 0.5 ML Ge and Xe buffer-layer thickness is 6 ML. (a) Arrhenius plot of PL integrated intensity for band P1 and P2 as a function of measurement temperature. (b) The PL peak shift with temperature of the P1 and P2 bands. The dashed line represents the Varshni relationship of Ge band gap