Enhanced Hall Mobility and d0 Ferromagnetism in Li-Doped ZnO Thin Films Prepared by Aerosol-Assisted CVD

Abstract

Zinc oxide (ZnO) thin films with different concentrations of lithium, from 0 to 15 mol%, have been grown on Si(100) substrates by employing aerosol-assisted chemical vapor deposition (AACVD). The structural, electronic, and magnetic properties of the ZnO thin films were investigated as the effect of Li doping concentration. SEM images of surface morphology reveal that the undoped and low-concentration Li-doped ZnO thin films exhibit irregular ellipsoid grains. In comparison, the ZnO thin films with higher Li concentration consist of multi-aligned rod-like and hexagonal-shaped grains. XRD pattern analysis confirms that all grown ZnO thin films exhibit a single polycrystalline phase of hexagonal wurtzite crystal. The lattice reduction was observed in the Li-doped thin films indicating that the substitutional Li effectively occupied the Zn lattice site. The Hall effect measurement demonstrates that Li-doped ZnO films possess p-type conductivity. The resistivity of Li-doped ZnO thin films decreases with an increase in Li doping concentration while the hole carrier density increases. The Hall mobility tends to increase as more Li doping concentration is given, with the highest Hall mobility obtained from 15 mol% Li-doped film with a value of 85.88 cm²/V s. The VSM study demonstrates that all grown ZnO thin films exhibit an M-H hysteresis curve, indicating d⁰ ferromagnetism behavior at room temperature, with coercivity ranging from 202 to 373 Oe. The highest saturation magnetization was obtained from 10 mol% Li-doped films, with a value of 5.55 × 10^–2 emu/g.

Graphical Abstract