Over the last decades, continuous technological advancements have been made in III‐nitride light‐emitting diodes (LEDs), so that they are considered as a promising replacement of traditional light sources. With the emission wavelength covering the entire visible spectrum, InGaN LEDs find various applications such as solid‐state lightings, full‐color displays, and visible light communication. However, the quantum efficiency of InGaN LEDs suffers from a dramatic decline as the emission wavelength extends from blue to green–red region. This issue restrains the lighting and display applications based on the color‐mixing monolithic lighting source system. In this review, the recent breakthroughs in long‐wavelength InGaN LEDs, together with the challenges and approaches to realize high‐indium‐composition InGaN epilayers, are introduced. These cover the different epitaxial substrates, nucleation layers, and epitaxial structures, especially multiple quantum wells active region. The related studies are also discussed to improve the long‐wavelength LEDs performance from the aspect of crystal quality, growth orientation, carrier‐injection, and 3D nanostructures. Finally, current status and perspectives for future long‐wavelength LEDs development are proposed briefly.

Here, we propose nanoimprinted patterned sapphire with a silica array (PSSA) with the aim to promote the efficiency of InGaN-based green (∼520 nm) mini-LEDs. According to x-ray diffraction measurements, the threading dislocation density of GaN epitaxial layers grown on nanoimprinted PSSA demonstrates a pronounced reduction compared with the epilayers on the conventional patterned sapphire substrate (PSS). Consequently, a mini-LED on PSSA exhibits a significantly boosted light output power (LOP) in comparison to a mini-LED on PSS. At 10 mA, the LOP of the mini-LED on PSS is 6.0 mW, and this is further improved to 6.8 mW for the mini-LED on PSSA. Moreover, the peak external quantum efficiencies of the mini-LEDs on PSS and PSSA are 41% and 47%, respectively. A three-dimensional (3D) finite-difference time-domain simulation demonstrates that the PSSA contributes enhanced light extraction for photons emitted from the active region. It is also highly feasible to use this nanoimprinted PSSA technology in red and blue mini-LEDs for the realization of full-color displays.

Highly efficient indium gallium nitride (InGaN)-based yellow light-emitting diodes (LEDs) with low efficiency droop have always been pursued for next-generation displays and lighting products. In this work, we report an InGaN quantum barrier (QB) with linear-increase In-composition along [0001] direction for InGaN-based yellow LEDs. With the In-composition in QBs systematically engineered, three QB structures including linear-increase QB (LIQB), linear-decrease QB (LDQB) and commonly used flat QB (FQB) were investigated by simulation. The results show that the LIQB not only yields enhanced electron confinement, but also contributes to suppressed polarization field. Consequently, the yellow LED incorporated with LIQBs demonstrates improved radiative recombination rates and the efficiency droop is alleviated. Under a current density of 100 A/cm2, the efficiency droop ratios of LEDs with FQBs, LDQBs and LIQBs are 58.7%, 62.2% and 51.5%, respectively. When current density varies from 1 A/cm2 to 60 A/cm2, the blueshift values of peak emission wavelength for LEDs with FQBs, LDQBs and LIQBs are 14.4 nm, 16.5 nm and 13.0 nm, respectively. This work is believed to provide a feasible solution for high-performance InGaN-based LEDs in long-wavelength spectral region.