Spectrally Pure, High Operational Dynamic Range, Deep Red Micro-LEDs

III-nitride-based micro-light-emitting diodes (micro-LEDs) are currently under rapid development for next-generation high-resolution and high-brightness displays and augmented/virtual reality (AR/VR) technologies. However, it remains elusive to achieve red-emitting III-nitride micro-LEDs with a microscale size, high efficiency, and high spectral stability, posing significant impediments to the development of full-color micro-LEDs. In this work, through detailed strain engineering and control of charge carrier transport, we achieved pure red emission (≥620 nm) micro-LEDs over 2 orders of magnitude of injection current variation. We show both theoretically and experimentally that the combination of a short-period InGaN/GaN superlattice and a thick n-type GaN interlayer can not only relieve the quantum-confined Stark effect in the active region but also suppress parasitic emission from the superlattice. The optimized deep red micro-LEDs with a device lateral dimension of ∼1 μm feature a maximal external quantum efficiency of over 3% emitting at ∼660 nm.