Anisotropic misfit strain relaxation in lattice mismatched InGaAs/GaAs heterostructures grown by MOVPE

The relaxation process in InGaAs/GaAs heterostructures with a small lattice mismatch (less than 1%), grown by metalorganic vapour-phase epitaxy (MOVPE), has been investigated by means of high-resolution X-ray diffraction (HR-XRD). Transmission electron microscopy (TEM) revealed a two-dimensional (2D) network of 60° misfit dislocations formed at the (0 0 1) interface in the two orthogonal 〈1 1 0〉 crystallographic directions. The structural analysis by X-ray diffractometry was performed with the samples oriented either in the [1¯ 1 0] or the [1 1 0] perpendicular directions, using reciprocal lattice mapping. The observed anisotropic-strain relaxation, related to the asymmetry in the formation of α and β misfit dislocations along [1¯ 1 0] and [1 1 0] directions, respectively, causes distortion of the epilayer unit cell and lowers its symmetry to orthorhombic.