The dependence of the structural and optical properties on the CdTe epitaxial layer thicknesses in CdTe (111)/GaAs (100) heterostructures

Abstract

X-ray diffraction (XRD), transmission electron microscopy (TEM), and spectroscopic ellipsometry measurements on the CdTe (111) epitaxial layers grown on the GaAs (100) substrates by molecular beam epitaxy were carried out to investigate the dependence of structural and optical properties on the CdTe epitaxial layer thickness. TEM measurements show that there is a lattice mismatch between the CdTe layer and the GaAs substrate and that the CdTe layers are twinned due to the strain. The spectroscopic ellipsometry spectra show that the critical-point energy shifts monotonically with decreasing the thickness of the CdTe epilayer. The results of the XRD curves show that compressive strains exist in CdTe layers thinner than 1.9 μm. As the strain calculated from the XRD spectra increases, the values of the critical-point energy-shifts obtained from the spectroscopic ellipsometry measurements increase linearly. These results indicate that the strains in the CdTe layers grown on GaAs substrates decrease with increasing the CdTe layer thickness.