Maximum Limits on External Quantum Efficiencies in Bare LEDs

Inevitable self-heating effects have been investigated for LEDs to date. In this paper, we present the thermally-induced penalty (TIP), and derive an upper external quantum efficiency (EQE) limit for a given bare LED by adding TIP to the real EQE. We find that the red-AlGaInP LED exhibits no efficiency droop under room temperature and the TIP is responsible for its real EQE droop. Among the TIPs of red, green, and blue LEDs, the red-AlGaInP LED suffers the most severe penalty. This TIP can serve as a criterion for LED cooling design, with its lower values leading to higher cooling rates.