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InGaN-Based Blue Light-Emitting Diodes Grown on Epitaxially Laterally Overgrown GaN Substrates

InGaN single-quantum-well-structure blue light-emitting diodes (LEDs) were grown on epitaxially laterally overgrown GaN (ELOG) and sapphire substrates. The emission spectra showed the similar blue shift with increasing forward currents for both LEDs. The output power of both LEDs was almost the same, as high as 6 mW at a current of 20 mA. The LED on sapphire had a considerable amount of leakage current in comparison with that on ELOG. These results indicate that the In composition fluctuation is not caused by dislocations, the dislocations do not act as nonradiative recombination centers in the InGaN, and the dislocations forms the leakage current pathway in InGaN.

InGaN-GaN multiquantum-well (MQW) blue and green light-emitting diodes (LEDs) were prepared by organometallic vapor phase epitaxy, and the properties of these LEDs were evaluated by photoluminescence (PL), double crystal X-ray diffraction, and electroluminescence (EL) measurements. It was found that there were only small shifts observed in PL and EL peak positions of the blue MQW LEDs when the number of quantum well (QW) increased. However, significant shifts in PL and EL peak positions were observed in green MQW LEDs when the number of QW increased. It was also found that there was a large blue shift in EL peak position under high current injection in blue MQW LEDs. However, the blue shift in green MQW LEDs was negligibly small when the injection current was large. These observations could all be attributed to the rapid relaxation in green MQW LEDs since the In composition ratio in the InGaN well was high for the green MQW LEDs. The forward voltage Vf of green MQW LEDs was also found to be larger than that of blue MQW LEDs due to the same reason.


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