We report on ferromagnetic characteristics of Zn 1Ϫx Mn x O ͑xϭ0.1 and 0.3͒ thin films grown on Al 2 O 3 (00•1) substrates using laser molecular-beam epitaxy. By increasing the Mn content, the films exhibited increases in both the c-axis lattice constant and fundamental band gap energy. The Curie temperature obtained from temperature-dependent magnetization curves was 45 K for the film with xϭ0.3, depending on the Mn composition in the films. The remanent magnetization and coercive field of Zn 0.9 Mn 0.1 O at 5 K were 0.9 emu/g and 300 Oe, respectively. For Zn 0.7 Mn 0.3 O, the remanent magnetization at 5 K increased to 3.4 emu/g.

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High-quality ZnO thin films were grown epitaxially at 250-550°C Al 2 O 3 (00и1) substrates using low-pressure metalorganic vapor phase epitaxy. The reactants for the growth were diethylzinc and oxygen. Growth temperature, one of the important experimental parameters for epitaxial layers, was optimized. The films grown at 500°C exhibited good crystallinity and strong ultraviolet absorption and emission. Photoluminescence spectra of the films showed a dominant excitonic emission with a weak deep level emission. More importantly, a strong stimulated emission peak was observed even at room temperature.

We report on the observation of “hole” whispering gallery lasers from semiconductor microcavities with three dimensional optical confinement, with thresholds potentially reducible to micro- to nanoampere regimes according to a quadratic size-dependent reduction, consistent with a photonic quantum corral effect of naturally formed recombinant quantum rings. If the device size grows over a critical diameter, the quantum ring whispering gallery then begins to disappear. However, cooperative small hole laser arrays, exhibiting photonic crystal structure properties, avoid the criticality and open a possibility of constructing practical high-density electropumped emitter arrays.

We report polarization characteristics of light from a photonic quantum ring ͑PQR͒ laser of three-dimensional ͑3D͒ whispering gallery modes. The 3D polarization states of light from the PQR laser were studied with a home-built solid-angle scanner capable of detecting the spatial intensity distribution in a wide range of solid angles. The analysis shows that the dominant polarization vectors of the PQR laser emitting in the surface normal direction lie always tangential to the PQR perimeter, which means there is a strong carrier-photon coupling.