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Hard and conductive carbon nanodome thin films deposited by rf magnetron sputteringAluminum oxide films were grown by reactive magnetron sputtering. In order to maintain a stable deposition process and high deposition rate, a pulsed direct current bias was applied to the aluminum target and the substrate. An external solenoid was used to form a magnetic trap between the target and the substrate. The influence of substrate temperature, substrate bias, and the magnetic trap on film growth and properties was studied by different surface and thin-film analysis techniques and electrical measurements. Normally, amorphous alumina films were produced. However, under optimum process conditions, crystalline alumina films can be obtained at temperatures as low as 250°C, with a hardness ϳ20 GPa and excellent electrical insulating properties.
We describe the microstructure and optical properties of near-ultraviolet InGaN-GaN light-emitting diodes (LEDs) fabricated onto conventional and patterned sapphire substrates (PSSs) using metalorganic chemical vapor deposition. The PSS LED with an optimized hole depth (1.5 µm) shows an improvement of the room-temperature photoluminescence intensity by one order of magnitude compared with that of the conventional LED. As much as a 63% increased light emission intensity of the PSS LED was obtained at a forward current of 20 mA. For a typical lamp-form PSS LED (at 20 mA), the output power and external quantum efficiency were estimated to be 10.4 mW and 14.1%, respectively. The increase of the output power could be partly due to the improvement of the internal quantum efficiency upon decreasing the dislocation density, which was further confirmed by the transmission-electron-microscopy and etch-pit-density studies for the GaN-on-PSS samples. Moreover, the emitted light scattering at the GaN/PSS interface could also contribute to the enhancement of light extraction efficiency.
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