We report visible (red) lasing emission from Eu-doped GaN thin films grown on sapphire substrates. The edge emission fulfills the requirements of stimulated emission properties: super-linear characteristic, spectrum line narrowing, polarization effect, lifetime reduction, and longitudinal modes in a Fabry–Perot cavity. The GaN:Eu active layer has low threshold (∼10 kW/cm²) for the onset of lasing. The optical gain and loss are of the order of 50 and 20 cm⁻¹, respectively. Growth conditions are investigated for gain enhancement and loss reduction. To obtain the high gain and low loss active layer, N-rich growth conditions are required. Channel waveguide cavities result in 5× increase in gain value compared to planar waveguides.

GaN films were grown on sapphire by molecular beam epitaxy (MBE). Two sources of activated nitrogen were investigated: an electron cyclotron resonance (ECR) plasma, and hydrogen azide (HN3). With the ECR plasma source, typical growth rates were ∼ 0.1 μm/h. Films grown in this manner showed significant surface damage from ions, and little if any photoluminescence. With HN3, growth rates were ∼ 0.25 μm/h. Azide-grown films showed smooth surfaces, and sharp band-to-band photoluminescence. This is the first reported use of HN3 to grow III–V nitrides by MBE, and it shows great promise as a nitrogen source.


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Large-size, two-dimensional Y Ba2Cu3O7 (YBCO) films were successfully prepared by a chemical solution-based coating pyrolysis (CP) process on 30 × 10 cm2 R-plane sapphire substrates with a vacuum-deposited CeO2 buffer layer. The CeO2 layer was very smooth and uniform with an average roughness (Ra) of 0.48 nm by atomic force microscopic observations and highly-oriented by large-area x-ray diffraction θ–2θ scans. The c-axis-oriented YBCO films were prepared by a CP process using a fluorine-free, metal acetylacetonate-based coating solution. A 30 × 10 cm2-rectangular c-axis-oriented YBCO film annealed in a large-diameter tube furnace demonstrated high inductive-Jc values, for which the distribution was fairly uniform, with an average 1.0 MA cm−2 at 77 K.

Epitaxial Naβ″-Al2O3 single crystal films have been grown into sapphire substrates. The kinetic measurements and calculation indicate that the β″-Al2O3 crystal is formed via chemical reactions between the gaseous alkali-species and sapphire substrate which are controlled by diffusion of oxygen species in the solid phase. The mechanism and crystallographic translations of film-growth are discussed.


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In the Verneuil sapphire crystal growth system, the alumina powder is molten during its fall into an oxygen-hydrogen flame. The liquid droplets fall on the top of the slowly-pulled crystal. From a physical point of view, the Verneuil process is complex because of the coupling of the turbulent combustion between hydrogen and oxygen, the hydrodynamics of the gas phase and the heat transport by convection, conduction and radiation.

Numerical simulations of the Verneuil crystal growth process have been carried out using the FIDAP finite element software, and the results have been presented in a previous paper. In order to determine the effect of the transparency of the sapphire, some assumptions were used: the process is considered in quasi-steady state, the model is axi-symmetric and the latent heat of fusion is negligible, i.e. the powder is not included in the model. The results obtained in the case where the crystal is considered as opaque have been compared with the simulation of a fully transparent material. Numerical simulation of heat transfer in transparent and semitransparent crystal growth processes.

The transparent crystal appears to be cooler than the opaque one, because in a transparent body the absorption of heat is reduced. The axial thermal gradient in the opaque crystal is smaller than that calculated in the case of a transparent crystal. By comparing the numerical results with experimental thermocouple data, it has been concluded that the simulation of a fully transparent sapphire crystal is more realistic than that of an opaque one.

A further step in this study will be to analyse the effect of the participating media radiation through the sapphire.

Vertical Bridgman method for growing fluoride crystals.


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ZnO nanorods were synthesized on formula /sapphire substrates using a modified thermal-evaporation process. The as-synthesized Formula nanorods and thin films were characterized using scanning electron microscopy, micro-Raman, and X-ray diffraction techniques. The morphology of the Formula changes from nanorods to continuous thin films when the growth temperature increases to 800°C. Further increase in the growth temperature leads to a lower growth rate of Formula along the direction. Micro-photoluminescence measurements show ultraviolet band-edge emission peaks around Formula from both nanorods and thin films. Realization of such Formula structures may be useful for the fabrication of hybrid Formula optoelectronic devices.

Recent results suggests that Formula may be a p‐type transparent conductor, but thin film synthesis is difficult because of the complex Formula phase diagram. We report a robust method of making c‐axis oriented Formula thin films. Thin film precursors of formula were deposited on sapphire substrates by radio‐frequency sputtering and by pulsed‐laser deposition. Subsequent annealing in air at Formula in a closed crucible containing Formula and Formula powders yielded nearly phase‐pure, biaxially textured Formula . The film were p‐type and transparent with a gap of Formula .


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