Molecular beam epitaxial growth and optical properties of the CdTe thin films on highly mismatched SrTiO₃ substrates

High-quality (111)-orientated CdTe thin films are grown epitaxially on SrTiO₃ (001) substrates by molecular beam epitaxy (MBE). The evolution of epitaxial growth was in-situ monitored by reflection high energy electron diffraction. The surface morphologies of the CdTe epitaxial layers (CTELs) are characterized by atomic force microscope, and atomic flat surface is confirmed as the thickness of the CTELs is below ∼40 nm. Three types of X-ray diffraction, including single crystal ω-2θ scan, double crystal X-ray rocking curve and φ-scan, are performed to characterize the structural quality of the CTELs. A full width at half maximum of ∼110 arcsec is yielded when the thickness of the CTELs is beyond ∼100 nm supported by the X-ray rocking curve. And φ-scan illustrates the appearance of four types of domains in the CTELs. Finally, direct band transition is determined, and the temperature dependent transmittance spectra exhibit that the optical band gap decreases from 1.581 eV to 1.503 eV with the temperature from 10 K to 300 K because of the electron-phonon interaction and the lattice thermal expansion.