Surface relaxation of strained semiconductor heterostructures revealed by finite-element calculations and transmission electron microscopy

Surface relaxation of a cross-section strained In 0.13 Ga 0.87 As layer buried in GaAs is studied by finite-element calculations and transmission electron microscopy (TEM). Strain fields in the In 0.13 Ga 0.87 As layer and in the cladding layers are calculated by the finite-element method and they are then used to compute the corresponding TEM image contrast, in the framework of the column approximation. A good qualitative match between experimental and computed TEM images is obtained, which demonstrates that, using the column approximation, the finite-element approach can be adapted to this type of study. The sensitivity of TEM contrasts to parameters such as foil thickness, deviation parameter, anomalous absorption and chemical composition is also analysed. In particular, the results of our exhaustive study, of TEM contrasts as a function of foil thickness show that surface strain relaxation is significant whatever the foil thickness and that this relaxation should not thus be mistaken for what is commonly called "thin-foil effects".