Sub-micrometer and nanoscale optoelectronic devices, including light emitting diodes (LEDs) and laser diodes, have drawn considerable attention, as they are essential for future large scale, or ultra-large scale integration of electronic and optoelectronic devices on a single chip. To date, however, it has remained extremely challenging to achieve high efficiency micro or nanoscale optoelectronic devices. One noticeable example is the efficiency cliff related to micro-LEDs, i.e., a drastic reduction in device efficiency with reducing dimensions. Micro-LEDs have been considered as the essential building block for emerging virtual/augmented reality devices and systems, due to their ultrahigh brightness, low power consumption, ultrahigh integration density, superior stability, and long lifetime. Shown in Fig. 1, external quantum efficiency (EQE) in the range of 50%–70% has been commonly measured for AlGaInP-based large area LEDs (lateral dimensions ), whereas the efficiency drops to negligible values for devices with lateral dimensions of the order of 10 μm.
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