Lattice strain analysis of VPE-Grown ZnS epitaxial layers on (001) GaAs by RES - Channeling and high resolution XRD measurements

Lattice deformation and built-in residual strain have been determined in hydrogen transport vapour phase epitaxy (VPE) grown ZnS epilayers on (100) GaAs. Ion channeling - Rutherford backscattering spectrometry (RES) has been used to evaluate the overall crystalline quality of the ZnS epilayers. X-ray diffraction measurements in both double-axis (DA) and single axis modes have been performed to determine the residual ZnS strain tensor and the reciprocal orientation between ZnS and GaAs lattices. High crystalline quality can be achieved at the surface of relatively thick ZnS layers (greater than or equal to 1 mu m), althought a dense distribution of extended defects can be inferred close to the ZnS/GaAs interface from the dechanneling yield. The analysis of DA measurements performed along several symmetric and asymmetric reflections at different azimuthal angles shows that the ZnS unit cell is slightly orthorhombically distorted. The thermal misfit between ZnS and GaAs and the ZnS linear expansion coefficient have been determined by temperature dependent X-ray diffraction between room temperature and the growth temperature (650 degrees C). Systematic measurements of the ZnS lattice strain compared with the measured thermal strain indicate that initial lattice misfit at the growth temperature is almost totally relaxed even for relatively thin layers.