Phosphorus donors in highly strained silicon
  The hyperfine interaction of phosphorus donors in fully strained Si thin films grown on virtual Si$_{1-x}$Ge$_x$ substrates with $x\leq 0.3$ is determined via electrically detected magnetic resonance. For highly strained epilayers, hyperfine interactions as low as 0.8 mT are observed, significantly below the limit predicted by valley repopulation. Within a Green's function approach, density functional theory (DFT) shows that the additional reduction is caused by the volume increase of the unit cell and a local relaxation of the Si ligands of the P donor. 
Hans Huebl, Andre R. Stegner, Martin Stutzmann, Martin S. Brandt,   Guenther Vogg, Frank Bensch, Eva Rauls, Uwe Gerstmann