Anisotropy of strain relaxation in heterogeneous GaInNAs layers grown by AP-MOVPE

• TEM and XRD were used for characterizing undoped GaInNAs layers grown by MOVPE.
• Heterogeneous layer structure and gradient compositions were revealed.
• Asymmetric formation of misfit dislocations evoked anisotropy of strain relaxation.
• Modified band structure and epitaxial layer unit cell parameters were calculated.
• Optimized growth conditions are needed to avoid structural inhomogeneities.

The structural investigations of thick undoped GaInNAs/GaAs heterostructures grown by atmospheric pressure vapor phase epitaxy (AP-MOVPE) have been performed by transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The cross-sectional view TEM images revealed plainly heterogeneous layer structure, consisting of a few sublayers with different indium and nitrogen contents. On the other hand, planar-view TEM images revealed 2D network of misfit dislocations oriented in two orthogonal 〈110〉 crystallographic directions at the (001) sublayer interface. Moreover, the XRD measurements provide information about gradient profiles of indium and nitrogen contents, as well as distinct anisotropy of strain relaxation in GaInNAs epitaxial layer, evoked by the asymmetry in formation of interfacial misfit dislocation. The obtained results were exploited to calculate the band structure diagram of the investigated GaInNAs/GaAs heterostructure and mean values of the lattice parameters of the distorted epitaxial layer unit cell, respectively.