Spectrally stable red c-plane InGaN-based LEDs enabled by composition-graded AlGaN barriers

Red-emitting InGaN light-emitting diodes (LEDs) are highly sought after in next-generation micro-displays and visible light communication systems. In order to improve the luminescence performance of red LEDs, we report a graded Al content AlGaN barrier structure to alleviate internal polarization fields and suppress QCSE. Compared to red LEDs with a constant Al content, red LEDs with a graded Al content exhibit high spectral stability. They demonstrate an almost constant emission wavelength (620 nm) over a wide range of drive currents. Time-resolved photoluminescence (TRPL) confirms enhanced electron-hole overlap and faster radiative recombination in the graded structure, correlating with improved quantum efficiency and reduced efficiency droop. The results provide a practical route to overcome polarization-induced limitations in III-nitride optoelectronics. This approach has significant implications for micro-LED displays requiring strict color uniformity and for visible-light communication systems that demand high-speed, stable light sources.