Excitation wavelength dependent photoluminescence in structurally non-uniform Si/SiGe-island heteroepitxial multilayers

In nanometer-size Si/SiGe-island heteroepitxial multilayers grown on Si(001), low temperature photoluminescence spectra are observed that strongly depend on the excitation wavelength and show a strong correlation with structural properties revealed by transmission electron microscopy. These experimental results can be explained by assuming that the optically created carriers are strongly localized at Si/SiGe island heterointerfaces. We show that electron-hole pairs are generated and recombine within spatial regions mainly defined by the photoexcitation penetration depth, and that the estimated exciton diffusion length is notably short and comparable with the SiGe-island average size.