白光LED的加速老化特性

Characteristics of the Accelerated Aging White LEDs

对两组GaN基白光发光二极管(LED)进行了对比温度加速老化实验,环境温度分别是80,100℃。随着老化温度的升高,电流-电压(I-V)曲线的隧道电流段、扩散电流段以及反向漏电电流均增加,而串联电阻段则变化较小,这是位错密度升高和金属杂质沿着螺旋位错聚集及移动的结果;电容-电压(C-V)曲线中反向偏压下电容减少,正向偏压下电容增大,这是由于螺位错和混合位错产生了漏电的通道;电致发光光谱中黄光荧光成分比重增加;光通量随时间开始缓慢降低,在某一个时刻突然急剧降低,显示各个老化因素累积的影响会在某一时刻导致白光LED突然失效。最后使用阿列纽斯关系计算出所用白光LED的寿命为2.3万小时。

GaN-based white LEDs are becoming the most promising next generation lighting sources, but the normal encapsulated white LEDs luminous flux declines very quickly. It is very necessary to research on the aging mechanisms of white LEDs luminous efficiency, chromatic properties, and so on. Temperature accelerated aging experiments on two groups of white LEDs have been performed at 80 ℃ and 100 ℃. Both before and after the aging experin：lents, the current-voltage （I-V） curves of the white LEDs were measured. In the tunneling segment, diffusion segment and reversal leakage current segment of the current-voltage （I-V） curves, the current was increased, while that of the serial resistance segment was nearly unchanged. The cause of these rises was the increase of the threading dislocation density and that the metal impurities assembled around the screw threading dislocations and moved along them. At the same time, the high-frequency capacitance-voltage （ Csc-V） curves of the virgin white LEDs and the aged ones at different ambient temperature were measured. In the Csc-V curve, the capacitance decreased in the reversal bias, and it increased in the forward bias. It means that there are some leakage current channels produced by the dislocations. During all the aging time, Chroma parameters were measured every certain hours. The yellow luminescence proportion in the spectrum increased. In the beginning of the aging, the luminous flux decreased slowly, then it decreased rapidly and suddenly. This fact indicated that the accumulation of all degenerating factors could lead to sudden light-off of white LEDs. Finally, by using the Arrhenius relationship, the lifetime of the white LEDs used in our experiments was calculated as 23 000 h.