Deposition and Characterization of a Ferromagnetic Semiconductor Chromium Doped Zinc Oxide

Theoretical spintronic devices are based on electron spin. Realization of such devices requires successful injection of polarized electron spins into semiconductors. Direct injection from ferromagnetic metals is limited by conductivity mismatches between a metal and a semiconductor. The formation of dilute magnetic semiconductors is believed to be one possible solution to successful spin injection. Theories suggest zinc oxide (ZnO) doped with a transition metal will exhibit ferromagnetism. To date mixed results have been reported for such films. Chromium (Cr) doped ZnO (ZnO:Cr) films prepared by direct current (DC) reactive co-sputtering of Zn and Cr in the presence of argon (Ar) and oxygen (O) were characterized for potential use as a dilute ferromagnetic semiconductor. Formation of ZnO was confirmed by x-ray diffraction (XRD). Furthermore, ZnO grain growth was found to improve with annealing of the samples. At high Cr powers the films transitioned from ZnO to ZnCr2O4 and CrO2. The presence of Cr in the thin films was confirmed particle induced x-ray emission (PIXE), Rutherford backscattering (RBS), and x-ray photoelectron spectroscopy (XPS). The presence of iron (Fe) and sodium (Na) contaminants was also detected by the PIXE measurements. Room temperature ferromagnetism was observed in samples with 0 - 4.2 % Cr concentration. However, due to the presence of Fe contaminants detected by PIXE, the source of the ferromagnetism cannot be confirmed to be a result of Cr substitution in the ZnO lattice forming a ferromagnetic semiconductor