Magnetic, magnetotransport, and optical properties of Al-doped Zn0.95Co0.05O thin films

Thin films of 5% Co-doped ZnO with a range of Al codoping exhibit a band-edge shift, which varies with carrier concentration as n(2/3). Carrier effective mass is 0.26m(e) and mobility is similar to 10 cm(2) V-1 s(-1). The doped films, which contain coherent Co clusters of 4-8 nm in size, exhibit a ferromagnetic moment of 0.3-1.0 mu(B) per cobalt. The magnetism is progressively destroyed by Al doping due to a reduction in Co-cluster formation. Magnetoresistance appears below 30 K, but these materials cannot be regarded as dilute magnetic semiconductors. (c) 2007 American Institute of Physics.