GaN-based LEDs were fabricated on patterned-sapphire substrates with various pyramidal-pattern coverage percentages (31–81%). Three distinguish stages are observed in the behavior of the light out-put power against coverage percentage. By etching-pit density measurement, dislocation density is found to be independent with coverage percentage. The light extraction efficiency (LEE) should be the main mechanism for the enhancement in the light out-put power. LEE would be enhanced, when the pattern coverage is less than 39% or over 67%. The light extraction efficiency remains similar, when the pattern coverage in between 39% ∼ 67%.
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Lin et al. (2011) studied this question.
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