Local lattice distortion in Si1-x-yGexCy epitaxial layers from x-ray absorption fine structure

The local structure around Ge in an epitaxial him of Si1-x-yGexCy alloy is investigated by x-ray absorption fine structure. The interatomic distances and the Debye-Waller factors were determined as a function of the carbon concentration up to the third coordination shell. The most important effect of the introduction of C in the Si1-xGex matrix is the increase of static disorder with C concentration. This effect is larger for higher coordination shells. Molecular dynamics simulations show that this effect is due to the strong deformations induced by the small C atoms in the Si1-xGex matrix. The variation of interatomic distances as a function of C concentration and of the epitaxial strain is also discussed.