Comparison of characteristic properties of Al, Ga, and In-doped ZnO thin films formed by sol-gel method

Abstract

Herein, we examine the effect of doping with Indium (In), Gallium (Ga), and Aluminum (Al) (group III elements) on the structural, optical, and vibrational properties of ZnO thin films . The characteristic properties of the ZnO films prepared by the sol-gel dip-coating method are explored by utilizing X-ray diffraction, optical spectroscopy , and Raman scattering measurements. XRD analyzes exhibit that the crystallite size reduces upon doping by Ga and Al, while it increases with In, and all films have hexagonal wurtzite structure. Additionally, Raman measurements indicate that the dominant two peaks at around 104 and 445 cm −1 are related to E 2 low and E 2 high phonon modes of ZnO, respectively. The low-frequency mode ( E 2 low ) is affected by dopant atoms, whereas the high-frequency mode ( E 2 high ) of the wurtzite phase is not influenced by the dopant. Moreover, E dop-atom phonon mode appears at low frequencies and the intensity ratio, I( E dop.atom )/I( E 2 low ), decreases as the ionic radius of dopant atoms increases. UV–Vis spectra reveal that the film transparency, optical band gap, Urbach energy, and refraction index can be effectively tuned by dopant atoms. • Al, Ga and In-doped ZnO films are prepared by sol-gel dip coating method. • XRD and Raman spectra show that films have hexagonal wurtzite structure. • The intensity of E 2 low mode rises as the ionic radius of the dopant atom increases. • The optical band gap of In-doped ZnO reduces due to expansion of crystallite size. • Raman and XRD measurements reveal that the films are under compressive stress.