High Color Rendering Index Hybrid III‐Nitride/Nanocrystals White Light‐Emitting Diodes

Abstract

An excellent hybrid III‐nitride/nanocrystal nanohole light‐emitting diode (h‐LED) has been developed utilizing nonradiative resonant energy transfer (NRET) between violet/blue emitting InGaN/GaN multiple quantum wells (MQWs) and various wavelength emitting nanocrystals (NCs) as color‐conversion mediums. InGaN/GaN MQWs are fabricated into nanoholes by soft nanoimprint lithography to minimize the separation between MQWs and NCs. A significant reduction in the decay lifetime of excitons in the MQWs of the hybrid structure has been observed as a result of the NRET from the nitride emitter to NCs. The NRET efficiency of the hybrid structures is obtained from the decay curves, as high as 80%. Moreover, a modified Förster formulation has exhibited that the exciton coupling distance in the hybrid structures is less than the Förster's radius, demonstrating a strong coupling between MQWs and NCs. Finally, based on a systemic optimization for white emission indexes, a series of hybrid ternary complementary color h‐LEDs have been demonstrated with a high color rendering index, up to 82, covering the white light emission at different correlated color temperatures ranging from 2629 to 6636 K, corresponding to warm white, natural white, and cold white.

Recent Progress in Quantum Dot Based White Light-Emitting Devices

“…As an alternative approach to increase the exciton transfer rate, and address the conflict between the need for close proximity of QWs and QDs and the use of a sufficiently thick capping layer on QW with a high current injection, top-down dryetched nanohole [126,127] or nanopillar [128][129][130][131] III-nitride structures have been demonstrated. Chanyawadee et al [126] designed a QW-QD system where [127], Ó 2015 Wiley InterScience elliptical holes filled with QDs reached down to multi-QWs (called deep-etched LED), so that more excitons could be transferred to QDs.…”

“…Chanyawadee et al [126] designed a QW-QD system where [127], Ó 2015 Wiley InterScience elliptical holes filled with QDs reached down to multi-QWs (called deep-etched LED), so that more excitons could be transferred to QDs. In this work, a reference LED--called shallow-etched LED in which QDs were far from multi-QWs--was fabricated.…”

“…Most recently, an excellent hybrid III-nitride (InGaN/ GaN)/nanocrystal (CdSe/ZnS) nanohole light-emitting diode (h-LED) was demonstrated as shown in Fig. 14, which generated white light with CRI up to 82, and tunable CCT ranging from 2629 to 6636 K [127]. In such WLEDs, various coloremitting QDs were blended into nanohole arrays, and high color conversion efficiency (up to 69 %) and high QY (up to 93 %) were achieved, attributed to an efficient energy transfer efficiency of 80 %.…”

Polarized white light from hybrid organic/III-nitrides grating structures

“…Furthermore, the emission from any standard c-plane LEDs is intrinsically unpolarised. A combination of CdSe/ZnS colloidal quantum dots with III-nitride blue LEDs has been used to achieve high performance white light sources demonstrating excellent CIE coordinates with high color rendering index (CRI)1011, although new regulations recently launched poses strict limitations to the usage of Cd-based quantum dots as a result of their toxicity which can be potentially hazardous to human health. Furthermore, this method still faces significant challenges in achieving polarized white light emission.…”

“…The calculation of the NRET efficiency has been carried out based on an approach introduced in refs 11 and 23. It is well-known that not all the MQW region contributes to the NRET process and that the NRET process can take place effectively only in the region with a 10 nm separation between the donor (InGaN MQWs) and the acceptor (F8BT) dipoles.…”