  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.
