Structural, optical and dielectric properties of (Co and Sm) co-implanting O-polar ZnO films on sapphire substrate

Highlights: • O-polar ZnO films on the sapphire substrate were prepared by molecular beam epitaxy. • Co ions and Sm ions were injected into O-polar ZnO films by ion implantation. • The structure, optical and dielectric properties of the films were studied. • The band gap of the co-implanted film was the smallest after ion implantation. • Dielectric constants of ZnO films were explored by spectroscopic ellipsometry. -- Abstract: In this paper, molecular beam epitaxy (MBE) was used to prepare O-polar ZnO films on the sapphire substrate. Co ions and Sm ions were respectively injected into the O-polar ZnO films by ion implantation, so that Co-implanted O-polar ZnO film, Sm-implanted O-polar ZnO film, and (Co and Sm) co-implanted O-polar ZnO film were prepared. We adopted X-ray diffraction (XRD), Atomic Force Microscope (AFM), Raman spectroscopy, photoluminescence spectra (PL), absorption spectroscopy and Spectroscopic Ellipsometry (SE) to study the structure, optical and dielectric properties of all samples. XRD showed that Co atoms and Sm atoms had entered the crystal lattice and the high-quality ZnO films had been prepared. Compared with the unimplanted sample, the surfaces of the implanted samples were granular and the roughness became larger. The co-implanted sample had the smaller roughness than the single-implanted samples. It was found from Raman spectra that two modes related to the LO vibration mode appeared near 50–230 cm⁻¹ and 520–570 cm⁻¹ after implantation. The PL spectra indicated that the intensity of the Sm-implanted sample was greater than the (Co and Sm) co-implanted sample. After ion implantation, the results measured by SE showed the band gap values of the (Co and Sm) co-implanted sample was reduced, and a transition peak around 3.15 eV appears in the second-order derivative spectra of the imaginary part ε₂ of the dielectric function. These paved the way for their application and development in optoelectronic devices.