Hybrid QD-LED Raises Efficiency

PQC LED hybridised with QD colour converters

(a) Schematic representation, (b) cross-sectional, and (c) top SEM images of a photonic quasi-crystal LED hybridised with QD colour convertersA

An international research group has used quantum dots to create a hybrid LED. QDs are embedded within the whole stack of the LED’s active layers. This photonic quasi-crystal LED structure boasts ‘record-breaking’ colour conversion effective quantum yields.

The first step was to grow an LED stack of GaN/InGaN Multi-Quantum Well (MQW) onto a sapphire substrate. Nano-imprint lithography and plasma etchings were then used to ‘punch’ the stack and structure as a 12-fold symmetric quasi-crystal (PQC). The structure formed an array of 480nm-radius cylindrical holes, with a lattice pitch of 750nm. It was etched deep enough to penetrate through the whole MQW active area and filled with a blend of QDs, deposited through a spin coating process.

QD emitters, in this architecture, are placed near to the MQWs of the active area. The researchers write that this improves the out-coupling efficiency between MQWs and QDs, which enables a non-radiative resonant energy transfer between the two, and near-field radiative coupling of trapped (guided) modes in the LED to the emitters.

Effective quantum yields reached 123% for single QD species colour converters, and around 110% for a white blend of three commercially-available QDs (green (535nm), yellow (585nm) and orange (630nm)). These achieved a ‘quasi-perfect’ 6,500K D65 spectrum. It is thought that performance could be further improved using nanocrystalline emitters.

The work can be found at

The research group was made of staff from two Schools (Electronics & Computer Science and Physics & Astronomy) at the University of Southampton (UK); Luxtaltek Corporation (Taiwan); the Department of Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University (Taiwan); and the Centre for Photonics and Quantum Materials, Skolkovo Institute of Science and Technology (Russia). Funding was supplied by the Royal Society; the Engineering and Physical Sciences Research Council; the UK-India Education and Research Initiative; and the Ministry of Science and Technology of the People’s Republic of China.