Lattice distortion in InxGa1-xAs/InP epitaxial films: A second- and third-shell XAFS study

We investigate the lattice distortion of pseudomorphic epitaxial InxGa1-xAs/InP thin films by polarization-dependent x-ray absorption fine-structure spectroscopy; five samples with In concentration in the range 0.25-0.75 and strain ranging from tensile to compressive have been investigated. We find that the measured second- and third-shell distances exhibit a clear dependence on the angle between the photon beam and the sample normal, in agreement with the expected tetragonal distortion of the unit cell. A method is proposed to extract from the polarization-dependent measurements the values of the strain-induced split of second- and third-shell interatomic distances. The values obtained by this method are in excellent agreement with the predictions of a model that calculates the variations of interatomic distances due to strain by applying the macroscopic strain tensor at local scale and linearly summing the known alloying effect. This model was applied successfully to the first shell distances in previous papers; the application to the second and third shells is a further confirmation of the validity of the model in the InxGa1-xAs structure