Virtual-crystal approximation and alloy broadening of intersubband transitions in p-type SiGe superlattices - art. no. 125308

The predictions of quantized state energies as calculated by the empirical pseudopotential method (EPM) and by the 6x6 k.p model, both within the virt ual-crystal approximation (VCA), are compared for the case of SiGe based qu antum wells grown in the [001] direction. Furthermore. the accuracy of the VCA is tested by performing the EPM calculation with enlarged supercells co mprising a number of minimal-volume supercells with a number of different c onfigurations of pure Si or Ge atoms over the lattice sites. The accuracy o f the VCA is found to be excellent (with errors less than 1 meV), and the a greement between the EPM and k.p is very good for energies up to a few hund red meV away from the valence band top. Finally, the influence of alloy dis order on the transition matrix elements, and the broadening of intersubband transitions due to fluctuations of the alloy composition and atomic config uration, are discussed.