Nanorings with an average height and diameter of 1.2 and 65 nm, respectively, were observed to form in Si-capped Ge quantum dots grown at 600 °C by ultrahigh-vacuum chemical vapor deposition. The nanorings were captured with the rapid cooling of the samples with appropriate amount of Si capping. Based on the results of transmission electron microscopy and Raman spectroscopy, the formation of nanorings is attributed to alloying and strain relief in the Si/Ge/ ͑001͒Si system. The self-assembly of nanorings provides a useful scheme to form ultrasmall ring-like structure and facilitates the characterization of the physical properties of unconventional quantum structures.

Blue-light-emitting Si1−xGex oxide nanowires have been grown on epitaxial Si0.8Ge0.2 alloys on silicon by thermal annealing in a quartz tube furnace in N2 ambient. The photoluminescence spectrum of Si1−xGex oxide nanostructures exhibits the blue-light emission with a peak at 415 nm, compared with the Si oxide nanowires with a peak at 470 nm. Nanowires with uncommon shapes, such as sunflowerlike and radiolarialike shape, have been observed. A field emission scanning electron microscope was used to monitor the growth of nanowires on the same patterned catalytic Au region. The growth can be understood in term of vapor-liquid-solid mechanism.

Room-temperature electroluminescence at 1.3 and 1.5 μm from Ge/Si quantum-dot light-emitting diodes is reported. The devices were fabricated in a mesa-type structure, with a silicon oxide layer on the top for surface/sidewall passivation. Different passivation processes were employed. We found that the integrated electroluminescence intensities were relatively less sensitive to temperature, persisting at nearly the same intensity up to RT. The fabricated device shows an internal quantum efficiency of about 0.015% at RT. The improved emission property is attributed to the reduced nonradiative recombination centers due to the surface passivation and thermal treatment.

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