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In this research, experiments and optical simulations have been carried out to study the effect of bevelled sidewalls and geometric shapes on the light extraction efficiency of GaN LED chips. Besides the conventional rectangular chips, hexagonal LED chips were experimentally processed for the fist time on a novel island-like GaN substrate. The bevelled sidewalls could be naturally formed on the chips during the growth of GaN islands by HVPE technology. The results of simulations and experiments are consistent with each other, and show that the output power of LED will be improved doubly when the sidewalls were beveled on the chip. The light output from hexagonal LED chips is also proved better than that from conventional rectangular chips.

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