The Electroluminescence Spectra of InGaN/GaN Blue LEDs During Aging Time

The luminescence spectra of InGaN/GaN multiple quantum wells light-emitting diodes under low level injection current (<4 mA) during aging process was investigated for the first time. Comparing the electroluminescence (EL) spectra of LEDs before and after aging time it was found that the peak wavelength and the full width at half maximum (FWHM) decreased with stress time and the changes of EL spectrum had two different stages drastic decrease at the early stress stage and slow decrease later showing the same trend with the output optical power of LEDs, which indicates that the effective polarization electric field of LEDs becomes weak during the aging process and the change has a clear correlation with the increase of the defects in the multiple quantum wells of LEDs. Electrical measurement revealed that junction capacitance (C-j) under the same junction voltage (V-j =1. 8 V) and the junction voltage (V-j) with the same injection current 1 mA calculated by ac small-signal IV method increased along with aging time, which explicates that the carrier density under the same low injection increases as the aging time increases. Analyses indicate that the polarization field in the quantum well is more seriously screened by the increased carriers captured by defects activated during stress time, the weaker effective polarization electric field makes the tilt of the energy band smaller, the energy radiated through the band edge and the density of energy states of the band edge increase which leads to the behaviors of peak wavelength and the FWHM of InGaN/GaN multiple quantum wells LEDs under low level injection current.