Effects of Cr-doping concentration on the structural, optical, and magnetic properties of ZnO thin films

Cr-doped ZnO thin films have been prepared on silicon (100) substrates by a radio-frequency (RF) magnetron sputtering method. The crystallographic structures, optical, and magnetic properties of the thin films are investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and physical properties measurement system (PPMS), respectively. The XPS results confirm that the chemical-bonding state of the doped Cr ions is +3. XRD analyses reveal that the Cr ions successfully replace Zn atoms and incorporate into the crystal-lattice positions of ZnO. Magnetic measurements reveal that all the samples have ferromagnetic features and saturation magnetization increases on increasing the dopant concentration. Room-temperature PL spectra show an ultraviolet (UV) emission at 380nm and a green emission at 500nm, whose intensity is greatly increased with increased Cr dopant. Moreover, the results of PL further testify that ferromagnetism (FM) is an intrinsic property of the Cr-doped ZnO films and FM can be described by bound magnetic polaron (BMP) models with respect to defect-bound carriers. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim