We propose a widegap II–VI semiconductor alloy, ${\mathrm{Mg}}_x{\mathrm{Zn}}_{\text{1−x}}\mathrm{O},$ for the fabrication of heteroepitaxial ultraviolet light emitting devices based on ZnO. The $c$ -axis oriented ${\mathrm{Mg}}_x{\mathrm{Zn}}_{\text{1−x}}\mathrm{O}$ films were epitaxially grown by pulsed laser deposition on ZnO epitaxial films and sapphire (0001) substrates using ceramic targets. Solid solution films were prepared with Mg content up to $\text{x=0.33,}$ achieving a band gap of 3.99 eV at room temperature. MgO impurity phase segregated at $\text{x⩾0.36.}$ Lattice constants of ${\mathrm{Mg}}_x{\mathrm{Zn}}_{\text{1−x}}\mathrm{O}$ films changed slightly $\text{(∼1\%),}$ increasing in $a$ axis and decreasing in $c$ -axis direction with increasing $\mathrm{x.}$ These films showed ultraviolet photoluminescence at energies from 3.36 $\text{(x=0)}$ to 3.87 eV $\text{(x=0.33)}$ at 4.2 K.

Influences of point defects on the nonradiative processes in ZnO were studied using steady-state and time-resolved photoluminescence (PL) spectroscopy making a connection with the results of positron annihilation measurement. Free excitonic PL intensity naturally increased with the increase in the nonradiative PL lifetime (τnr). Density or size of Zn vacancies (VZn) decreased and τnr increased with increasing growth temperature in heteroepitaxial films grown on a ScAlMgO4 substrate. Use of homoepitaxial substrate further decreased the VZn density. However, τnr was the shortest for the homoepitaxial film; i.e., no clear dependence was found between τnr and density / size of VZn or positron scattering centers. The results indicated that nonradiative recombination processes are not solely governed by single point defects, but by certain defect species introduced by the presence of VZn such as vacancy complexes.

Epitaxial TiO₂ rutile films were fabricated on α-Al₂O₃ (1012) substrate in the layer-by-layer fashion by laser molecular beam epitaxy. Ablation with a Co-doped TiO₂ target produced single phase of rutile film with the concentration of Co between 0 and 5%. Some ferromagnetic domain structures were observed in Co _x Ti_1-x O₂ rutile films by a scanning superconducting quantum interference device microscope at 3 to 90 K. The magnetic hysteresis could also be observed even at room temperature with a magnetic moment of ∼ 1 µ_B/Co atom.

We propose a method of rapid construction of a structural–magnetic–electronic phase diagram of doped Mott insulators. The composition-spread method is utilized for fabricating a film whose doping concentration varies from 0 to 1 continuously. The concurrent x-ray diffractometer that measures x-ray diffraction spectra of all the composition simultaneously, the scanning superconducting quantum interference device microscope, and the infrared optical spectroscopy are employed for characterizing the film. A demonstration is given for a colossal magnetoresistive material, ${\mathrm{La}}_{\text{1−x}}{\mathrm{Sr}}_x{\mathrm{MnO}}_3.$