Photoluminescence of Ge nanocrystals self-assembled on SiO2

Ge nanocrystals have been obtained from the dewetting process during thermal annealing of an amorphous Ge layer deposited by molecular beam epitaxy on a thin SiO2 layer on Si(001). The Ge nanocrystals were then capped with a thin layer of amorphous Si. The mean nanocrystal size-2.5-60 nm-depends on the initial Ge layer thickness. Low-temperature photoluminescence (PL) measurements were performed to investigate quantum confinement effects on the Ge nanocrystal energy gap and defect states. For the present range of particle sizes, the nanoparticle PL emission appeared as a wide near-infrared band near 900 meV although a weak confined band was also observed for the smallest nanoparticles. Further thermal annealing of the samples increased the interband recombination by nearly two orders of magnitude.