dc and ac transport properties of Mn-doped ZnO thin films grown by pulsed laser ablation

Mn_xZn_1-xO (x = 0.20) thin films were deposited on Pt coated Si substrates using pulsed laser ablation technique. The structural characteristics of the films were investigated by X-ray diffraction (XRD), while the dielectric response of the films was studied as a function of frequency and ambient temperature by employing impedance spectroscopy. It was found that all the films deposited on Pt coated Si substrates had c-axis preferred orientation perpendicular to the substrate, with full width at half maximum (FWHM) of the (0 0 2) X-ray reflection line being less than 0.5°. The dc and ac electrical conductivity of Mn-doped ZnO films were investigated as a function of temperature. The ac conductivity, σ_ac(ω), varies as σ_ac(ω) = Aω^s with s in the range 0.4-0.9. The complex impedance plot showed data points lying on a single semicircle, implying the response originated from a single capacitive element corresponding to the bulk grains. The value of the activation energy computed from the Arrhenius plot of both dc and ac conductivities with 1000/T were 0.2 eV suggesting hopping conduction mechanism. The optical properties of Zn_0.8Mn_0.2O thin films were studied in the wavelength range 300-900 nm. The data were analyzed in the light of the existing theories and reflected a Burstein-Moss shift in these films. The films show magnetic properties, which are best described by a Curie-Weiss type behavior.