High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer

Abstract

We increased the light-extraction efficiency (LEE) of AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) by introducing a highly reflective photonic crystal (HR-PhC) into the surface of the p-AlGaN contact layer, thereby achieving a high external quantum efficiency (EQE). A low-damage HR-PhC with a lattice period of approximately 250 nm was fabricated using nanoimprinting and dry etching. A reflective Ni/Mg p-type electrode was deposited on the HR-PhC layer using a tilted-evaporation method. The EQE of a conventional DUV LED with emission around 283 nm was increased from 4.8 to 10% by introducing the HR-PhC and the reflective Ni/Mg electrode. A simple estimation of the effective reflectance of the HR-PhC p-AlGaN contact layer with the Ni/Mg electrode indicated a value exceeding 90%.

13 mW operation of a 295–310 nm AlGaN UV-B LED with a p-AlGaN transparent contact layer for real world applications

“…5,6,30,31 To achieve this goal, our group implemented an ''ammonia (NH 3 ) pulsed-flow multilayer (ML) growth technique'', with which good quality AlN layers grown on a (0001)-sapphire substrate, having FWHM values of the XRCs for the (0002) and (10-12) planes of 200 and 300 arcsec, respectively (TDD B1 Â 10 8 cm À2 ), could be obtained. 5,6,19,20,31 In this work, low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE), with trimethylgallium (TMGa) and trimethylaluminum (TMAl) as group-III precursors, and ammonia (NH 3 ) for the group-V element, was used to grow UV-B LED heterostructures on AlN templates grown on (0001)-oriented c-plane sapphire substrates. Tetraethylsilane (TESi) and bis(ethylcyclopentadienyl)magnesium (Cp 2 Mg) were used as n-and p-type doping sources, respectively.…”

“…Recently, our group reported an AlGaN UVC LED that uses a highly reflective photonic crystal (PhC) on a p-AlGaN contact layer, with which an EQE of 10% was successfully achieved. 19 Our group, in collaboration with Panasonic Corporation, successfully achieved a world record EQE of 20% from an experimental AlGaN based UVC-LED grown on an AlN buffer layer on a patterned sapphire substrate (PSS). 20 UV Craftory, Nitek, and Nichia have also developed some DUV LEDs using AlGaN or InAlGaN.…”

“…5,6 However, the LEE of our UV LED devices is still under 10%. 5,6,19,20,28,29 The EIE of the 310 nm-band UV-B LED is also very low. It is therefore necessary to further improve LEE and EIE in the AlGaN UV-B LED devices.…”

Influence of Undoped‐AlGaN Final Barrier of MQWs on the Performance of Lateral‐Type UVB LEDs

“…The improved EQE of 5.6% at 20 mA and maximum light output power of 17 mW at 82 mA dc drive measured on bare‐wafer level conditions in Lat‐UVB LED are relatively small, when compared with those obtained from flip‐chip‐based deep ultraviolet light‐emitting diodes (DUV LEDs), using photonic crystal (PhC) in p‐AlGaN (p‐GaN) as well as using lens‐like packaging . Therefore, further improvement in the Lat‐UVB LEDs is expected, by using flip‐chip technology, PhC in p‐AlGaN (p‐GaN), polarization doping, and lens‐like packaging …”

Enhancing the light extraction of AlGaN-based ultraviolet light-emitting diodes in the nanoscale

“…38 Kashima et al 27 introduced a highly reflective PhC (HR-PhC) into the surface of the p-AlGaN contact layer to induce the vertical light-propagation. According to their results, the effective reflectance of the HR-PhC p-AlGaN contact layer with the Ni/Mg electrode exceeded 90%.…”