InGaN／GaN多量子阱蓝光发光二极管老化过程中的光谱特性

摘要

系统地研究了小注入电流（＜4mA）下InGaN/GaN多量子阱结构蓝光发光二极管的发光光谱特性在老化过程中的变化。对比老化前后的电致发光（EL）光谱，发现在注入电流1mA下的峰值波长（peakwavelength）和半高宽（FWHM）随老化时间增加而减小，变化过程分两个阶段：前期（＜100h）减小速度较快，而后逐渐变缓，呈现出与LEDs的发光光功率一致的变化规律，说明LEDs的等效极化电场在老化过程中减弱，这一变化和量子阱内缺陷的增加有明确的关系。通过电学特性测量发现同一结电压（Vj＝1.8V）下的结电容Cj和由交流小信号I-V方法计算得到的注入电流1mA下的结电压Vj随老化时间增加而增大，明确了在同等小注入电流下量子阱内的载流子浓度随老化过程增加。分析表明在老化过程中InGaN/GaN多量子阱结构蓝光发光二极管量子阱内的缺陷及其束缚的载流子数量增加，形成了增强的极化电场屏蔽效应，减弱的等效极化电场导致了量子阱的能带倾斜变小，带边辐射复合能量增大，能态密度增多，对应的发光过程的峰值波长变短（蓝移），半高宽变窄。%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 be-fore 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 mul-tiple quantum wells of LEDs .Electrical measurement revealed that junction capacitance (Cj ) under the same junction voltage (Vj=1.8 V) and the junction voltage (Vj ) 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 increa-ses .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 .