Near-ultraviolet nitride-based light-emitting diodes (LEDs) with peak emission wavelengths around 410 nm were fabricated onto c-face patterned sapphire substrates (PSS). It was found that the electroluminescence intensity of the PSS LED shown 63% larger than that of the conventional LED. For a typical lamp-form PSS LED operating at a forward current of 20 mA, the output power and external quantum efficiency were estimated to be 10.4 mW and 14.1%, respectively. The improvement in the light intensity could be attributed to the decrease of threading dislocations and the increase of light extraction efficiency in the horizontal direction using a PSS
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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