Coexistence of fast and slow luminescence in three-dimensional Si/Si1-xGex nanostructures

We report an experimental observation of both a fast (∼10μs) and a slow (∼10ms) photoluminescence (PL) that coexist in Ge-rich (x>0.5) islandlike, three-dimensional Si/Si1-xGex nanostructures. We present a quantitative model that explains the observed PL lifetime dependence on carrier concentration, temperature, and detection wavelength. The PL dynamics are found to be determined by the excess carrier concentration: the fast PL is associated with a dynamic type I and the slow PL with a type II energy band alignment in Ge-rich Si/SiGe nanostructures.