Growth and photoluminescence properties of inclined ZnO and ZnCoO thin films on SrTiO₃(110) substrates

ZnO thin film growth prefers different orientations on the etched and unetched SrTiO₃(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 ZnCoO100//STO1\bar10 and ZnCoO1\bar11//STO001. The low temperature photoluminescence spectra of the inclined ZnO and ZnCoO films are dominated by D⁰X emissions associated with A⁰X emissions, and the characteristic emissions for the ²E(²G)→⁴A₂(⁴F) transition of Co²⁺ dopants and the relevant phonon-participated emissions are observed in the ZnCoO film, indicating the incorporation of Co²⁺ ions at the lattice positions of the Zn²⁺ ions. The c-axis inclined ZnCoO film shows ferromagnetic properties at room temperature.