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Tunnel-junction micro-LEDs with 45% wall-plug efficiency

27 d ago

Researchers in China have developed tunnel-junction (TJ) blue micro-LEDs achieving a wall-plug efficiency (WPE) of 45.23%, as reported in Optics Express (June 2026). The team from Xiamen University, the Future Display Institute of Xiamen, and Nanjing University designed a device structure that eliminates the need for post-growth thermal annealing typically used to activate magnesium doping in p-type gallium nitride (p-GaN). This avoids thermal-induced epitaxial degradation, particularly damage to the indium gallium nitride (InGaN) multiple quantum wells (MQWs) that emit blue light. The micro-LEDs are intended for ultra-high-definition displays in virtual/augmented reality (VR/AR) and other systems, offering advantages like higher resolution and lower power consumption. The key innovation is a top n-GaN layer grown at a low temperature (865°C) to promote island-like growth, creating gaps that allow hydrogen to escape from the buried p-GaN, activating it without thermal annealing. The growth sequence used metal-organic chemical vapor deposition on patterned sapphire substrates, with a 20nm highly doped p+-GaN layer, a 3nm n-InGaN layer, a 20nm n+-GaN layer, and finally a 300nm lightly doped n--GaN layer. The 10μm island-structured TJ (Isl TJ) micro-LEDs were compared with a reference device having a smooth top n--GaN layer grown at 950°C. Without rapid thermal annealing (RTA), the Isl TJ devices produced nearly double the spectral electroluminescence intensity and more uniform emission, attributed to better current spreading and activation. They achieved a low voltage of 2.99V, output power of 2.55μW at 20A/cm² injection, and a peak WPE of 45.23%. RTA degraded both performance and uniformity, damaging the MQWs. The rough surface of Isl TJ also enhanced light extraction by suppressing total internal reflection. This WPE surpasses other reported blue LEDs with TJ (3.4%) or indium tin oxide (up to 34.3%) structures. The researchers note that this work paves the way for annealing-free tunnel-junction micro-LEDs in vertically stacked full-color displays and high-brightness lighting applications.