Understanding different efficiency droop behaviors in InGaN-based near-UV, blue and green light-emitting diodes through differential carrier lifetime measurements

TL;DR

This study investigates how efficiency droop in GaN-based LEDs varies with wavelength by measuring differential carrier lifetimes, revealing that longer lifetimes in green LEDs lead to higher carrier leakage and concentration, affecting efficiency.

Contribution

The paper provides a detailed analysis linking carrier lifetime differences to efficiency droop behaviors across near-UV, blue, and green LEDs, highlighting the role of polarization-induced quantum confinement Stark effect.

Findings

Longer carrier lifetimes in green LEDs increase carrier leakage.

Higher carrier concentration correlates with more severe efficiency droop.

Temperature effects on efficiency are explained by carrier lifetime variations.

Abstract

Efficiency droop effect under high injection in GaN-based light emitting diodes (LEDs) strongly depends on wavelength, which is still not well understood. In this paper, through differential carrier lifetime measurements on commercialized near-UV, blue, and green LEDs, their different efficiency droop behaviors are attributed to different carrier lifetimes, which are prolonged as wavelength increases. This relationship between carrier lifetime and indium composition of InGaN quantum well is believed owing to the polarization-induced quantum confinement Stark effect. Long carrier lifetime not only increases the probability of carrier leakage, but also results in high carrier concentration in quantum well. In other words, under the same current density, the carrier concentration in active region in near-UV LED is the lowest while that in green one is the highest. If considering the efficiency droop depending on carrier concentration, the behaviors of LEDs with different wavelengths do not show any abnormality. The reason why the efficiency droop becomes more serious under lower temperature can be also explained by this model as well. Based on this result, the possible solutions to conquer efficiency droop are discussed. It seems that decreasing the carrier lifetime is a fundamental approach to solve the problem.