Electronic structure of Ge-Si superlattices grown on Ge (001)

The authors have studied the electronic energy structure of pseudomorphic Ge_m/Si_n superlattices by using the empirical tight-binding method. Effects of the band offset, sublattice periodicity and the lateral lattice constant on the transition energies have been investigated. They found that Ge_mSi_n superlattices grown on Ge (001) can have a direct band gap, if m+n=10 and m=6. However, optical matrix elements for in-plane and perpendicular polarized light are negligible for the transition from the highest valence band to the lowest conduction band state at the centre of the superlattice Brillouin zone.