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There is growing interest in microLED devices with lateral dimensions between 1 and 10 μm. However, reductions in external quantum efficiency (EQE) due to increased nonradiative recombination at the surface become an issue at these sizes. Previous attempts to study size-dependent EQE trends have been limited to dimensions above 5 μm, partly due to fabrication challenges. Here, we present size-dependent EQE data for InGaN microLEDs down to 1 μm in diameter fabricated using a process that only utilizes standard semiconductor processing techniques (i.e., lithography and etching). Furthermore, differences in EQE trends for blue and green InGaN microLEDs are compared. Green wavelength devices prove to be less susceptible to reductions in efficiency with the decreasing size; consequently, green devices attain higher EQEs than blue devices below 10 μm despite lower internal quantum efficiencies in the bulk material. This is explained by smaller surface recombination velocities with the increasing indium content due to enhanced carrier localization.
Smith et al. (Tue,) studied this question.