Photoluminescence Efficiency of Self Assembled Ge Dots

For self assembled Ge dots, the predicted nonlinear increase in the photoluminescence (PL) efficiency with decreasing dot diameter has been evaluated using the dot size distribution observed from atomic force microscopy and transmission electron microscopy. The dots were formed by thermal annealing of an amorphous Ge layer deposited by molecular beam epitaxy on a thin insulating layer of either TiO$_{2}$/SiO$_{2}$ or just SiO$_{2}$ [1] on Si(001). For the present range of particle sizes (2.5 to 60 nm), the dot PL appeared primarily as a wide near-infrared band near 800 meV. The peak energy of the PL band reflects the average dot size and its shape depends on the dot size distribution. Using theoretical calculations for the band gap energy, the PL energy spectrum was transformed into the PL variation with dot size. The present results show how, conversely, dot size distributions can be obtained from PL data. \\[4pt] [1] N.L. Rowell, et al., J. Electrochem. Soc. 156, H913 (2009).