Room-temperature fabrication of epitaxial ZnO thin films on polymer substrates coated with a seed layer of exfoliated β-Ga₂O₃ single-crystal thin sheets by pulsed laser deposition

Abstract

Room-temperature (RT) epitaxial growth of ZnO thin films on flexible cyclo-olefin polymer (COP) substrates coated with the exfoliated β-Ga₂O₃(100) single crystal thin sheets as a seed layer was investigated using the pulsed laser deposition technique. Scanning electron microscopy (SEM) observations and X-ray diffraction (XRD) measurements demonstrated that c-axis-oriented epitaxial ZnO(0001) thin films were obtained at RT on the exfoliated β-Ga₂O₃(100) seed layer bonded to the COP substrate. Also, the epitaxial relationship between the ZnO thin films and β-Ga₂O₃(100) seed layer was ZnO(0001)/β-Ga₂O₃(100) with ZnO[1120] ∥ β-Ga₂O₃[010] and ZnO[1100] ∥ β-Ga₂O₃[001]. The optical transmittance of the thin film, including the seed layer was more than 80 % in the visible light region. The optical band gap and the electrical resistivity of the ZnO thin film were estimated to be about 3.4 eV and about 2.1 × 10⁻³ Ω cm at RT, respectively.