Investigations on strain relaxation of MOVPE grown ZnSxSe1-x layers

We investigated the strain relaxation process of ternary ZnS~Se~ .~ layers using high-resolution X-ray diffractometry (XRD), Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM). The samples were grown by low pressure MOVPE on (001) GaAs substrates. XRD analysis shows that after exceeding a critical layer thickness strain relaxation occurs first in the [1]-0] direction and the layer unit cell is monoclinically distorted. A detailed structural characterization and strain measurements for various compositions and layer thicknesses were carried out. TEM and RBS channeling measurements reveal an anisotropic distribution of defects not confined at the interface. Their contribution to the observed strain relaxation will be discussed. It is demonstrated that the introduction of a thin ZnSe layer between substrate and ZnSxSet_,. epilayer will drastically slow down the relaxation process and hamper the formation of stacking faults at the heterointerface.