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-xGexSi1-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.