We report the structural, electrical and thermopower properties of un-doped and Al doped zinc oxide (ZnO) thin films. Al doping was carried out using 25 keV Al+ implantation with 0.1, 1 and 2% Al into ZnO. X-ray diffraction measurements showed that the lattice parameters were larger than the bulk values, which is consistent with the incorporation of Al atoms at interstitials. Al doping increased the electrical conductivity from 100 (Ωcm)-1 in the un-doped ZnO film to 598 (Ωcm)-1 in the 2% Al doped ZnO film. Electron doping by Al resulted in an increase in the carrier concentration and it had an advantageous effect on the mobility where it was highest for 2% doping. The absolute value of the Seebeck coefficient systematically increased for un-doped, 1% and 2% Al doped ZnO films where the room temperature values were -50.8, -60.9 and -66.3 μV/K, respectively. The power factor increased significantly from 2.58 × 10-5 W/mK2 in un-doped ZnO film to 2.63 × 10-4 W/mK2 in 2% Al doped ZnO film. Our results suggest that the ion beam method is a suitable technique to enhance the thermoelectric properties of ZnO.
We report magnetoresistance measurements on epitaxial films of the intrinsic ferromagnetic semiconductor GdN electron doped with ∼1020cm−3 to ∼1021cm−3. The magnetoresistance across the temperature range of 10–300 K is dominated by a reduction of spin-disorder scattering in the presence of a magnetic field, imposing a resistance reduction of 27% in a field of 8 T. We show that the magnetoresistance closely follows the magnetic disorder as signaled by the departure of the magnetization from its fully saturated value Ms of 7μB/Gd3+.
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