OPTICAL-ABSORPTION OF PSEUDOMORPHIC SI GE SUPERLATTICES/

The optical properties of pseudomorphic (defect-free) (Si)n/(Ge)n stra ined-layer superlattices grown on Si1-xGex (001) substrates are studie d within the framework of the empirical tight-binding method. Attentio n is focused on the nature (direct/indirect) of the fundamental energy gap and on the effects of the superlattice periodicity on the optical absorption near the band edge. The band-edge absorption is the main d istinguishing feature among different superlattices. It is found that the behavior of the absorption is strongly dependent on light polariza tion (anisotropy) and substrate lattice constant. The contribution of the lowest interband transitions to absorption spectra is also analyze d. Theoretical results are compared with recent experimental data.