Persistent photoconductivity in MgZnO alloys

The electrical characteristics and persistent-conductivity effects in MgZnO:P alloys grown by the method of pulsed laser deposition on undoped n-ZnO substrates are systematically investigated. It is shown that the pronounced persistent conductivity and the persistent photocapacitance related to the presence of high-barrier electron traps for electron capture are observed in initial unannealed layers. These traps are located in the lower half of the band gap and have the optical ionization threshold of 2.8 eV and the electron-capture barrier height of ～0.4 eV. Alongside such centers, the hole traps with the ionization energy of 0.14 eV are also observed. The annealing at 850°C transforms the material into that of p-type conductivity with the depth of dominant phosphorus-related acceptors close to 0.2 eV. The conductivity compensation and the formation of hole traps with the activation energy of 0.14 and 0.84 eV in the n-ZnO substrate are also observed, and these traps are associated with the acceptor-defect diffusion into the substrate at annealing.