Micro-LEDs are emerging as a key technology for next-generation displays, particularly for virtual- and augmented-reality applications, where high brightness, high resolution, and high integration density are required. III-nitride LEDs on polar c-plane offer a mature and industrially compatible platform for micro-LEDs. However, the strong polarization electric field (PEF) in these devices induces the quantum confined Stark effect (QCSE), leading to reduced luminous efficiency, emission wavelength instability, and increased lateral carrier diffusion length. These issues are particularly important for high-performance micro-LEDs, where wavelength stability and carrier confinement are both critical.
Weak-PEF quantum wells (QWs) offer a feasible route to address these problems. Compared with nonpolar or semipolar orientations and quantum-dot approaches, weak-PEF LEDs on polar c-plane can suppress the QCSE while maintaining compatibility with established epitaxial growth and device fabrication processes. However, weak-PEF LEDs have still been limited by insufficient luminous efficiency, and their lateral carrier confinement capability for micro-LEDs remains to be verified.
In a new paper published in Light: Science & Applications, a team of researchers, led by Professor Yuantao Zhang from Jilin University, and co-workers have realized wafer-scale high-efficiency weak-PEF III-nitride blue LEDs on the polar c-plane by optimizing the epitaxial growth process. The devices reach the highest peak external quantum efficiency (EQE) among their kind and show great wavelength stability. Importantly, weak-PEF LEDs demonstrate strong lateral carrier confinement, leading to less efficiency degradation from sidewall effects than conventional GaN-based MQWs LEDs. This work opens an effective approach for the high-efficiency weak-PEF LEDs and provides a viable pathway toward high-performance micro-LED applications.
In weak-PEF QWs, the barrier layer is a key structure for reducing the PEF. InGaN/AlGaN digital alloy (DA) barriers provide a flexible material platform for this purpose. However, the epitaxial growth of DA barriers suffers from interface ambiguity and defect formation, which limits further improvement of device performance. To address this issue, the team systematically compared the effects of different pulse-growth modes during metal-organic chemical vapor deposition (MOCVD) growth on DA barriers. The results show that NH3 delivery during the AlGaN growth period is a key factor affecting the quality of DA barriers. A pulse-growth mode with modulated NH3 flow rate can effectively improve the interface quality of DA barriers, suppress the formation of related defects, and significantly enhance the optical performance of weak-PEF QWs.
Based on the optimized pulse-growth mode of DA barriers, the team further realized 4-inch industrial-scale preparation of weak-PEF InGaN/DA MQWs LEDs on the polar c-plane using industrial mass-production MOCVD. The prepared LED wafer exhibits good wavelength uniformity. Compared with conventional InGaN/GaN MQWs LEDs, weak-PEF LEDs show better wavelength stability, indicating effective suppression of the PEF in the QWs. Meanwhile, optimization of the pulse-growth mode significantly enhances the efficiency of weak-PEF LEDs, with the highest peak EQE of this kind.
Beyond high efficiency and wavelength stability, micro-LED applications also require effective control of lateral carrier diffusion. Enhancing lateral carrier confinement is critical for suppressing sidewall effects in micro-LEDs. By comparing the carrier diffusion behavior of weak-PEF LEDs and conventional InGaN/GaN MQWs LEDs, the team found that weak-PEF LEDs exhibit a shorter lateral carrier diffusion length. This makes their peak EQE less sensitive to sidewall effects by approximately 50%, providing an effective route to suppress efficiency degradation induced by sidewall effects in small-size micro-LEDs.
