Theoretical investigation of near gap electronic states of Si/SiGe multiple quantum wells on (001)-Si or SiGe substrates

We present a theoretical study of the near gap electronic states of Si/Ge based multiple quantum well systems composed of Si and Si1-xGex alloys coherently grown on (001)-Si or SiGe substrates. We interpret the experimental photoluminescence spectra recently reported [S. R. Sheng , Appl. Phys. Lett. 83, 857 (2003); 83, 2790 (2003)] in terms of direct or indirect k-space transitions. The effect of the spatial localization of the valence and conduction states is analyzed. We investigate the structures in the experiments within the tight binding renormalization method. Strain conditions, spin orbit effects, and quantum confinement are fully considered. Our calculations give an accurate description of the near gap experimental photoluminescence peaks.