Optical Properties of Si−Ge Semiconductor Nano-Onions

We explore theoretically the possibility of obtaining efficient light emission from Si−Ge semiconductor nano-onions. Our motivation stems from the strong luminescence recently observed from II−VI nano-onions, combined with the technological significance of the Si−Ge system. We calculate the electronic properties of a range of hypothetical Si−Ge nano-onions using the tight-binding method and determine the combination of size, strain, and materials which optimizes the production of visible luminescence. We predict that small (less than around 30 Å diameter) Si-covered Ge nano-onions will be visible light emitters.