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Nanophotonic Semin Conductors Lab.

Research

Surface plasmon-enhanced InGaN-based LEDs

We demonstrated the SP-enhanced InGaN/GaN MQWs blue LED with silver nanoparticles inserted into the n-GaN or the p-GaN layer of LEDs because the enhancement of local electromagnetic fields is strongly dependent on the distance between the MQWs and the metal nanoparticles. The internal quantum efficiency and optical output power of LEDs were significantly improved by the coupling between exciton dipole in MQWs and SPs. Furthermore, we developed SP-enhanced green and ultraviolet LEDs by using gold and platinum, respectively.

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Enhanced light extraction from GaN-based LEDs with nanostructure

We reported the development of GaN-based LEDs with PCs, which was formed inside p-GaN or n-GaN layer with SiO2 pillar and outside the p-bonding electrode on p-GaN layer. As a result, the optical output power was greatly enhanced by PCs compared to that without PCs. In addition, we also confirmed that internal quantum efficiency was increased by PCs which were embedded p-GaN or n-GaN layer.

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We also reported the light extraction efficiency of LEDs with ITO SWS dependent on the periodicity. Compared to the light output power of LEDs with flat ITO, the light output powers of LEDs with non-periodic and periodic ITO SWS were increased by gradient refractive index of SWS. In addition, we reported that the light output power of LEDs with periodic ITO SWS was higher than that of non-periodic ITO SWS. This indicates that periodic ITO SWS has more perfect gradient index profile.

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High-power LEDs with improved efficiency droop

In order to improve the efficiency of LEDs, the electron blocking layer (EBL) has played an important role in effectively confining electrons in the MQWs region of LEDs. We investigated the effect of the p-AlGaN EBL on efficiency droop in InGaN/GaN MQWs LEDs. At the low current density, LEDs with an EBL show a higher EQE than LEDs without an EBL. However, LEDs without an EBL show a higher EQE at high current density. The suppression of efficiency droop in LEDs without an EBL at high current density is attributed to an increased hole injection efficiency.

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