Excitonic properties of ordered and disordered SiGe nanocrystals

The excitonic properties of ordered and disordered Si/Ge nanocrystals (NCs) are investigated by means of ab initio calculations. In the former group, we investigate Si(core)/Ge(shell) and Ge(core)/Si(shell) NCs, while alloyed Si1-xGex NCs are studied in the latter focusing on the role of the molar fraction x. Concerning ordered NCs, we show that Ge/Si (Si/Ge) NCs exhibit type II confinement in the conduction (valence) band. As for disordered NCs, we show that optical gaps and radiative recombination lifetimes decrease with x. (c) 2008 Elsevier Ltd. All rights reserved.