Photoluminescence Efficiency of Self-Assembled Ge Nanocrystals

Abstract

For self-assembled Ge nanocrystals (NCs), the predicted nonlinear increase in the photoluminescence (PL) efficiency with decreasing NC diameter has been evaluated using the NC size distribution observed from transmission electron microscopy. The NCs were formed by thermal annealing of an amorphous Ge layer deposited by molecular beam epitaxy on a thin layer on Si(001). For the present range of particle sizes (2.5–60 nm), the NC PL appeared primarily as a wide near-IR band near 800 meV. The peak energy of the PL band reflects the average NC size, and its shape depends on the NC size distribution. Using both the and tight binding models, the PL energy spectrum was transformed into the PL variation with NC size. For smaller diameter NCs, the band shape contains significant bandgap enlargement due to quantum confinement. The present results show how NC size distributions can be obtained from the PL data.