Current Components and Their Temperature Dependence of Green and Blue Light-Emitting Diodes: A Quantitative Comparison

We have quantitatively compared the portion and temperature dependence of each current component in commercial green and blue light-emitting diodes (LEDs) using a current-component analysis method for the purpose of finding out the origin of the green-gap problem, which is a major roadblock to the next-generation solid-state lighting. The analysis results show that the loss current, which is the origin of the efficiency droop, decreases the internal quantum efficiency of the green LED significantly and is the primary origin of the green-gap problem. In addition, the loss current I_loss and the radiation current I_rad that actually generates light output are approximately related as I_loss ∝ I_rad^1.5 almost independent of the temperature. Therefore, I_loss and I_rad^1.5 have the similar temperature dependence in both the green and blue LEDs, and the loss current is approximately proportional to the cube of the carrier concentration. The temperature and the carrier-concentration dependences are valuable clues to the physical origin of the green-gap problem and the efficiency droop. On the other hand, the portion and the temperature sensitivity of the Shockley-Read-Hall (SRH) nonradiative recombination current are similar in the green and blue LEDs. Therefore, in our samples, the SRH nonradiative recombination is not the origin of the green-gap problem.