Red emission from strain-relaxed bulk InGaN active region.

High-In-content InGaN quantum wells (QWs) in red light-emitting diodes (LEDs) are typically grown at low temperatures to ensure effective In incorporation. In this study, red LEDs based on bulk InGaN active region were demonstrated. The growth temperature of bulk InGaN was ∼800℃, which is over 100℃ higher than the typical growth temperature of red QWs. By introducing high-density trench structures in the underlying green multi-quantum wells (MQWs), the compressive strain in bulk InGaN was relaxed by ∼96%. With strain relaxation, phase separation occurred in the bulk InGaN, forming low-In-content (blue) and high-In-content (red) phases. The red phase acted as carrier localization centers, enabling red light emission under electrical injection. The red LEDs based on bulk InGaN active region exhibited superior wavelength stability, with the peak wavelength shifting slightly from 648.6 nm at 1 mA to 642.4 nm at 100 mA. Meanwhile, the on-wafer peak external quantum efficiency was measured to be 0.32%. To the best of our knowledge, this study presents a new epitaxial strategy for red InGaN LEDs.