Effect of Alloying and Pressure on the Band Structure of Germanium and Silicon

The pseudopotential method has been used to compute the band structure of germanium-silicon alloys and the band structure of germanium under high pressure. In the former case the parameters were chosen from a linear interpolation between the parameters used previously for pure germanium and pure silicon, while in the latter case a simplified expression for the pseudopotential parameters based on the orthogonalized plane wave method was used to estimate their variation with lattice constant. The results are in reasonable agreement with experimental observations on the variation with pressure and alloying of the principal band edges. The calculations also indicate that the first absorption peak due to direct transitions should have a much larger pressure coefficient in Ge than in Si.