Enhanced efficiency of near-UV LEDs by surface plasmon and magnetic field effects from metal films

The enhanced efficiency of the near-UV (NUV) LEDs was demonstrated by the combinatory effects of surface plasmons (SP) from the Ag p-electrode and out-of-plane magnetic fields from additional Co/Pt multi-layers. By utilizing an InGaN/GaN-based NUV-LED epilayer including either 100 or 40 nm p-GaN layers, four different flip-chip LEDs were fabricated by selectively adding Co/Pt ferromagnetic multi-layers on the Ag p-electrode. NUV-LEDs with Co/Pt ferromagnetic multi-layers on 100-nm-thick p-GaN showed a 10.1% enhancement of integrated electroluminescence (EL) intensity at a forward current of 20 mA, mainly due to the out-of-plane magnetic field effect. In LEDs with a 40 nm p-GaN layer, which is consistent with the penetration depth of SP fields, a further increase of 13.8% can be achieved in the integrated EL intensity at 20 mA, resulted from the additional coupling effect with SP fields. These results indicate that the combination of Ag and Co/Pt multilayers, as the p-electrode of flip-chip LEDs, can increase the efficiency in NUV flip-chip LEDs due to efficient couplings of SP fields and an out-of-plane magnetic field with carriers injected into quantum wells.