Magnetic, magnetotransport, and optical properties of Al-doped Zn_(0.95)Co_(0.05)O thin films

摘要

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 ～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- 1.0μ_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.