The Origin of Efficiency in III-Nitride Micro-Light-Emitting Diodes

We demonstrate that the primary factor determining the external quantum efficiency (EQE) of InGaN-based micro-scale light-emitting diodes (µLEDs) depends on their internal state. A comparative photoluminescence (PL) study shows that the lateral diffusion length of carriers in InGaN red µLEDs is significantly shorter than in InGaN blue µLEDs, primarily due to inhomogeneity in the bulk material. This results in an insignificant change in PL intensity regardless of sidewall conditions. Additionally, examinations of EQE and peak wavelength across various epitaxial designs and sidewall conditions reveal that sidewall-surface recombination does not significantly impact EQE in InGaN red µLEDs. Meanwhile, the peak wavelength, which represents the radiative recombination rate given by the quantum well design of InGaN red µLEDs, is found to dominantly influence the EQE of InGaN red µLEDs. Furthermore, statistical analysis based on the relative standard deviation indicates that the peak wavelength is one of the primary determinants of EQE in InGaN red µLEDs. These findings suggest that addressing internal state is crucial for optimizing EQE of µLEDs.