Recent Progress in Long-Wavelength InGaN Light-Emitting Diodes from the Perspective of Epitaxial Structure

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.