Photoluminescence from ordered and disordered Si-SiGe superlattices

Ordered (Ord-SL) and disordered (Dis-SL) Si-SiGe superlattices are grown using ultrahigh vacuum chemical vapour deposition (UHVCVD). The results of cross-sectional transmission electron microscopy (XTEM) and high-resolution double crystal x-ray diffraction (HRXRD) indicate that high quality Si-SiGe superlattices can be achieved. Well-defined band-edge excitonic luminescence is observed for the Si0.86Ge0.14-Si superlattice. Stronger phosoluminescence (PL) is observed for the Si-SiGe disordered superlattice compared with the corresponding Si-SiGe ordered superlattice. Furthermore, PL peak energy of the Dis-SL shifts to lower value with respect to the peak position of the corresponding Ord-SL. The stronger intensity of the no-phonon (NP) peak and the red shift of the PL peak are possibly a result of two probable mechanisms: (i) the tunnelling effect and (ii) the formation of localized states.