Strain Analysis of CdTe on InSb Epitaxial Structures Using X-ray-Based Reciprocal Space Measurements and Dynamical Diffraction Simulations

The structural properties of CdTe layers grown by molecular beam epitaxy on (001) InSb substrates were assessed using high-resolution x-ray scattering methods. Triple-axis diffraction measurements and dynamical diffraction theory were employed to determine the strain in the epitaxial layer and at the interface for CdTe layer thicknesses of 1.0 μm and 1.8 μm. Reciprocal space maps were generated around the 004, 115, 224 and 335 reciprocal lattice points (RLP). An alignment procedure is described which ensured all reflections were aligned to the same zone axes. (335) reflections exhibited greater sensitivity to strain relaxation than (115) reflections due to a larger in-plane component; so these were used to better determine the strain state of the layers. Both of our 1.0-μm and 1.8-μm thick samples exhibited no relaxation, showing that pseudomorphic layers formed. Additionally, interference oscillations in the (004) ω:2θ scan of the 1.0-μm CdTe sample were observed. These oscillations were replicated through dynamical diffraction simulations by including a ∼1-nm highly strained interfacial layer. These results are consistent with an earlier electron microscopy study that detected a similar strained layer at a defect-free CdTe/InSb interface. The CdTe lattice parameter and Poisson ratio are determined to be 0.648201 ± 0.000002 nm and 0.408, respectively.