Growth and photoluminescence properties of inclined ZnO and ZnCoO thin films on SrTiO ₃(110) substrates

ZnO thin film growth prefers different orientations on the etched and unetched SrTiO ₃(STO)(110) substrates. Inclined ZnO and cobalt-doped ZnO (ZnCoO) thin films are grown on unetched STO(110) substrates using oxygen plasma assisted molecular beam epitaxy, with the c-axis 42° inclined from the normal STO(110) surface. The growth geometries are ZnCoO[100]//STO[110] and ZnCoO[111]//STO[001]. The low temperature photoluminescence spectra of the inclined ZnO and ZnCoO films are dominated by D ⁰X emissions associated with A ⁰X emissions, and the characteristic emissions for the ²E( ²G)→ ⁴A ₂( ⁴F) transition of Co ²⁺ dopants and the relevant phonon-participated emissions are observed in the ZnCoO film, indicating the incorporation of Co ²⁺ ions at the lattice positions of the Zn ²⁺ ions. The c-axis inclined ZnCoO film shows ferromagnetic properties at room temperature.