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

Abstract

Thin films of 5% Co-doped ZnO with a range of Al codoping exhibit a band-edge shift, which varies with carrier concentration as n23. Carrier effective mass is 0.26 me and mobility is ∼10 cm2 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 μB 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. © 2007 American Institute of Physics.