Cation impurity-defect complex induced ferromagnetism and hopping conduction in Sb-doped ZnO synthesized under high pressure

Abstract

Sb-doped p-type ZnO was synthesized using the high-pressure method with a quasi-equilibrium thermodynamic process. Room temperature ferromagnetism was observed in Sb-doped ZnO. The ferromagnetic coupling was found to be associated with zinc vacancies (VZn) induced by Sb doping, which was supported by a strong ultraviolet emission peak relevant to VZn in low temperature photoluminescence. Hall effect measurements indicated that the Sb-doped ZnO with Sb content of 3.4 at% had a hole concentration of 1.4 × 1020 cm−3 and low resistivity of 7.4 × 10−2 Ω cm. Temperature-dependent resistance measurements suggest that the electrical conduction mechanism of the Sb-doped ZnO changed from thermal activation model and nearest-neighbor hopping (NNH) conduction at high temperature to Mott variable-range hopping (VRH) and Efros–Shklovskii VRH conduction at low temperature. First-principles calculations demonstrated that the Sb impurity substituting Zn (SbZn) combines two VZn defects to form acceptor-like impurity-defect complex of SbZn–2VZn in ZnO due to the coulomb attraction. The SbZn–2VZn complex in Sb-doped ZnO are strongly correlated with ferromagnetic stability and lead to the Mott and Efro–Shklovskii VRH conduction at low temperature due to the localization of carriers at the complex impurity band.