LATTICE STRAIN FROM VALENCE-BAND HOLES IN SIGA ALLOYS

We use ab initio total-energy minimization techniques to resolve the lattice strain beta(h) arising from the presence of holes in the valence band of SiGa alloys. We find, in agreement with recent EXAFS results, the lattice to contract upon increasing the proportion of holes (beta(h) < 0). We also find that the valence-band deformation potential a(v) is positive, leading to a violation of Keyes' relation, which asserts that beta(h) and a(v) are equal within a constant positive factor. Our calculations suggest therefore that Keyes' formula does not describe adequately the relation between the two quantities, and also resolve the apparent contradiction between experiment and previous calculations.