Strain-engineered N-polar InGaN nanowires: towards high-efficiency red LEDs on the micrometer scale

The absence of efficient red-emitting micrometer-scale light emitting diodes (LEDs), i.e., LEDs with lateral dimensions of 1 μm or less is a major barrier to the adoption of microLEDs in virtual/augmented reality. The underlying challenges include the presence of extensive defects and dislocations for indium-rich InGaN quantum wells, strain-induced quantum-confined Stark effect, and etch-induced surface damage during the fabrication of quantum well microLEDs. Here, we demonstrate a new approach to achieve strong red emission ( > 620    nm ) from dislocation-free N-polar InGaN/GaN nanowires that included an InGaN/GaN short-period superlattice underneath the active region to relax strain and incorporate more indium within the InGaN dot active region. The resulting submicrometer-scale devices show red electroluminescence dominantly from an InGaN dot active region at low-to-moderate injection currents. A peak external quantum efficiency and a wall-plug efficiency of 2.2% and 1.7% were measured, respectively, which, to the best of our knowledge, are the highest values reported for a submicrometer-scale red LED. This study offers a new path to overcome the efficiency bottleneck of red-emitting microLEDs for a broad range of applications including mobile displays, wearable electronics, biomedical sensing, ultrahigh speed optical interconnect, and virtual/augmented reality.