KEYWORDS: Light emitting diodes, Internal quantum efficiency, LED lighting, Reliability, Light sources and illumination, General lighting, Quantum efficiency, Transmission electron microscopy, Packaging, LED backlight
Recent developements for highly efficient ligth emitting diodes are introduced. Multi-quantumwell
structure to improve the internal quantum efficiency, chip fabrication techniques to
increase the extraction efficiency, and packaging techniques with phosphor distribution
optimization are combined to obtain the efficient LEDs. Comparison between the several leading
products in the market has been performed to reveal the current LED techniques. The internal
quantum efficiency is found to be related to not only the dislocation density, but also the defect
size and type. Some key factors are reviewed on the reliability of LEDs which recently has been
improved a lot. For general lighting application, LM-80 test becomes the industry standard and
will be introduced briefly.
Mg-doped AlxGa1-xN is grown by metal-organic chemical vapor deposition to investigate the Ohmic characteristics of Pt and Ni/Au. The Al solid composition measured by x-ray varies from 0.04 to 0.19, while the atomic concentration of Mg confirmed by secondary ion mass spectroscopy spans from 3x1019 to 1x1020 cm-3. The Ohmic characteristics are measured by current-voltage by varying the Mg activation temperature, Ohmic metal annealing temperature, and annealing time. The specific contact resistance is 3.5 and 7.5x10-5 Ω cm2.with Pt and Ni/Au in p-Al0.085Ga0.915N and p-Al0.14Ga0.86N measured by circular transmission line model, respectively. These are the lowest ever reported in p-AlGaN.
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