Influence of a ZnTe buffer layer on the structural quality of CdTe epilayers grown on (100)GaAs by metalorganic vapor phase epitaxy

The influence of a ZnTe buffer layer on the structural quality of CdTe epilayers grown on (100)GaAs substrates by metalorganic vapor phase epitaxy has been investigated by both x-ray diffraction and ion channeling Rutherford backscattering spectrometry measurements. Single-crystal (100)-oriented CdTe epilayers of good structural quality have been obtained after inserting a ZnTe buffer layer of a thickness ranging between 300 and 500 nm. The influence of the buffer layer thickness on the crystalline quality and the morphology of the CdTe epilayer has been related to the defect distribution and the surface roughness of the ZnTe buffer layer. The crystalline quality and the surface strain have been thus studied as a function of the CdTe thickness on samples having optimal ZnTe layer thickness. The initial compressive mismatch between CdTe and ZnTe, f=-5.8%, appears to be almost fully relaxed for a CdTe thickness around 200 nm. A residual compressive in-plane strain (about -0.02%), independent of the CdTe epilayer thickness, has been found above 300 nm which can be ascribed to thermal strain and indicates a complete relaxation of the lattice misfit at the growth temperature.