The electronic and optical properties of silicon/germanium strained layer superlattices

An empirical pseudopotential scheme for the calculation of the electronic structure of lattice mismatched semiconductor superlattices is presented. In this method the strain is treated on a microscopic level. A scheme based on the nearly free electron model is used to determine the absolute energies of the constituents. The electronic structure of Si/Ge superlattices with period in the range 10 to 100 A is calculated using this method. The band alignment produced in the calculation is in close agreement with experiment and other calculational procedures. The inclusion of strain is found to be important in predicting the momentum mixing in the superlattice states. The enhancement of the optical transition across the fundamental gap is investigated in a variety of superlattices. The magnitude is found to depend on the confinement of the states and the magnitude of the momentum mixing. The inclusion of strain at a microscopic level is found essential in predicting the magnitude of the transition.