A novel method based on imprinting lithography and wet etching to fabricate a volcano-shaped patterned sapphire substrate (VPSS) is presented.

In this paper, the size effects on the efficiency droop (ED) in blue InGaN/GaN quantum well light emitting diode are investigated. The smaller size LEDs can work well under much higher power density, especially when the size is reduced to under 40 micro‐meters. It shows a weaker ED in these small LEDs. Time correlated single photon counting (TCSPC) measurements show a longer electroluminescence lifetime for smaller size LEDs, which implicates the nonradiative recombination is reduced. It is likely due to Aguer recombination reduction by quantum well (QW) band flatened with the device size decreasing. Cathodoluminescence results indicates that the strain in QWs is relaxed both in the whole pillar and along radial direction of the pillar. The better performance of the smaller size LED is likely attributed to strain relaxation (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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