Ge out diffusion effect on SiGe nanoring formation

Based on atomic force microscopy, high-angle annular dark-field scanning transmission electron microscopy, energy dispersive x-ray spectroscopy, and Raman spectroscopy, Ge outdiffusion effects on SiGe quantum dots to form nanorings are studied using the ultrahigh vacuum chemical vapor deposition. The epitaxial Si layer grown on quantum dots with SiH4 and H-2 precursors cannot cover the whole quantum dots, and the central area is passivated by the hydrogen. After annealing longer than 1 h at 500 degrees C in vacuum, the Ge atoms at the central area of quantum dots diffuse outward to form nanorings. However, the epitaxial Si layer grown with SiH4 and He precursors can cap all over the quantum dots, and the Si cap layer retards the Ge outdiffusion at the central area of quantum dots, resulting in 4 h annealing time. Moreover, for the uncapped quantum dots, the annealing in H2 also prevents the Ge outdiffusion at the central area and no nanorings are observed up to 5 h annealing at 500 degrees C. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3702812]