Exciton distribution-induced efficiency droop in green microscale light-emitting diodes at cryogenic temperatures

The anomalous droop in the external quantum efficiency (EQE) induced by the localization of excitons in GaN/InGaN green micro-light-emitting diodes (micro-LEDs) has been demonstrated at temperatures ranging from 25 to 100 K. At cryogenic temperatures, the random distribution of excitons among local potential energy minima limits the radiative recombination and reduces the EQE of green micro-LEDs. As the temperature increases from 25 to 100 K, the hopping of excitons from shallow potential energy minima to the potential energy valley contributes to the enhancement of radiative recombination. The distribution of excitons among local potential energy minima at cryogenic temperatures is also affected by the current density due to the influence of Coulomb screening of the polarization field and the band-filling effect.