Rational construction of staggered InGaN quantum wells for efficient yellow light-emitting diodes

High-efficiency InGaN-based yellow light-emitting diodes (LEDs) with high brightness are desirable for future high-resolution displays and lighting products. Here, we demonstrate efficient InGaN-based yellow (similar to 570nm) LEDs with optimized three-layer staggered quantum wells (QWs) that are grown on patterned sapphire substrates. Numerical simulations show that the electron-hole wavefunction overlap of staggered InGaN QWs with high In content exhibits a 1.7-fold improvement over that of square InGaN QWs. At the same injection current, LEDs with staggered QWs exhibit lower forward voltages and narrower full widths at half maximum than LEDs with square QWs. The light output power and external quantum efficiency of a staggered QW LED are 10.2 mW and 30.8%, respectively, at 15mA. We combine atomic probe tomography (APT), time-resolved photoluminescence (TRPL), and transmission electron microscopy (TEM) with energy-dispersive x-ray (EDX) mapping spectroscopy to shed light on the origin of enhanced device performance. APT results confirm the staggered In profile of our designed staggered QWs structure, and TRPL results reveal decreased defect-state carrier trapping in staggered QWs. Furthermore, TEM with EDX mapping spectroscopy supports the viewpoint that staggered QWs exhibit uniform elemental distribution and improved crystal quality. Together, these factors above contribute to enhanced LED performance. Our study shows that staggered InGaN QWs provide a promising strategy for the development of LEDs that are efficient in the long-wavelength region.