Misfit strain anisotropy in partially relaxed lattice-mismatched InGaAs/GaAs heterostructures

Partially relaxed InGaAs/GaAs heterostructures with a small lattice mismatch have been studied by means of atomic force microscopy and high-resolution x-ray diffractometry. Additionally, electron-beam induced current in a scanning electron microscope and transmission electron microscopy have been employed to investigate misfit dislocations formed at the (001) heterostructure interface. The measurements revealed a direct correlation between the surface crosshatched morphology and the arrangement of interfacial misfit dislocations. The reciprocal lattice mapping and the rocking curve techniques employed for the samples aligned with either the [(1) over bar 10] or the [110] crystallographic direction perpendicular to the diffraction plane revealed anisotropic misfit strain relaxation of the InGaAs layers. This anisotropy results from an asymmetry in the formation of the alpha and beta types of misfit dislocations oriented along the [(1) over bar 10] and [110] directions, respectively, which differ in their core structures. The misfit strain anisotropy causes a distortion of the unit cell of the layer and lowers its symmetry to orthorhombic.