OPTICAL-ABSORPTION OF STRAIN-SYMMETRIZED (SI)N (GE)10-N SUPERLATTICES/

Calculations of the optical absorption of short-period strain-symmetri zed (Si)n/(Ge)10-n superlattices, with n = 3-7, are presented. The cal culations are based on an empirical tight-binding model in the three-c entre representation, which includes third-neighbour and spin-orbit in teractions. These strained-layer superlattices (SLS) exhibit a direct gap. Their absorption coefficient, alpha(omega), is evaluated close to the bandgap, taking into account only direct transitions. The influen ce of the symmetry, the lattice constant in the growth plane and the c omposition of the SLS on the absorption coefficient is examined. It is found that among these materials the most appropriate for use in devi ces, such as receivers, is the strain-symmetrized (Si)4/(Ge)6 SLS.