Study of relaxed InxGa1-xAs epilayers by grazing incidence x-ray diffraction

Partially relaxed InxGa1-xAs films with high In content (x=0.35, 0.47), grown on GaAs(001) substrates, have been studied using grazing incidence x-ray diffraction techniques. By measuring the separation between the film peak and the substrate peak along different crystallographic directions, the in-plane lattice mismatch along these directions has been directly determined. We observed an asymmetric distribution of strain relief, the two [110] directions showing a stronger relaxation than the [100] direction. From the shift of peak positions as a function of the x-ray penetration depth, a strain relaxation gradient within the film has been determined, with the top layers more relaxed than those near the interface, In the thinnest films (5 nm thick) the presence of stacking faults was also found to relax the misfit strain. We used the grazing incidence x-ray diffraction technique for these measurements, with a novel approach that allowed the entire profile of the strain relaxation as a function of depth to be recorded in one measurement.