We demonstrate light extraction from metal reflector-based AlGaInP photonic crystal ͑PhC͒ light-emitting diodes ͑LEDs͒. The photons reflected by a high-reflectivity, small-absorption, bottom Ag mirror steadily interact with the PhC, and thus enhanced light extraction is achieved. The square lattice PhC patterns are fabricated on an upper n-doped AlGaInP surface with a depth of 500 nm. An optical power measurement using an integration sphere shows that the extraction efficiency of the PhC LED is ϳ1.8 times larger than that of the nonpatterned LED. A three-dimensional finite difference time domain simulation is performed to understand the output enhancement extracted by the PhC and the effect of internal absorption.
A vertical light-emitting diode (LED) with a chip size of 500 × 500 μm 2 was fabricated by the laser lift-off (LLO) process of an InGaN-based blue LED wafer. After the LLO process, photonic crystal patterns by UV nano-imprint lithography were formed on the n-GaN top layer of the vertical LED over the entire area with a diameter of 2 inches. As the result of n-GaN patterning, light output power of the vertical LED with photonic crystals was increased by up to 44% compared to that of the vertical LED without a photonic crystal at a driving current of 1000 mA.
In this paper we report on the selective area growth (SAG) of vertical GaN-based light-emitting diodes (LEDs) by low-pressure metal-organic chemical vapor deposition (MOCVD). SAG, under optimized growth conditions, leads to ridge-shaped epilayers with a smooth top surface, devoid of any surface defect structures. The final ridge-shaped vertical LED structures, after the removal of the sapphire substrate by laser lift-off (LLO), exhibit a smaller bowing effect than conventional vertical LED structures. The suppression of lateral strain in the epilayers is responsible for the smaller bowing effect because of the reduction in lateral dimensions. Consequently, the use of SAG LEDs can achieve a 21% higher light output power than conventional vertical LEDs, indicating a significant improvement in light extraction efficiency due to the light guiding pathways offered by the ridge-shaped geometry of the LED structures.
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