GaN基蓝绿光LED电应力老化分析

对InGaN/GaN多量子阱蓝光和绿光LED进行了室温20,40,60 mA加速电流下的电应力老化研究,发现蓝光与绿光样品经过60 mA电流老化424 h后,其电学性能表现出一定的共性与差异性:在小测量电流下,绿光样品的光衰减幅度较蓝光样品大~9%;而在较大测量电流 (20 mA)下,两者的光衰减幅度基本相同 (18%)。同时,蓝绿光样品的正向电学性能随老化时间的变化幅度基本一致,反映出它们具有相似的退化机制,绿光样品老化后增多的缺陷大部分体现为简单的漏电行为,而并非贡献于非辐射复合中心。在此基础上对GaN基外延结构进行了优化,优化后的LED长期老化的光衰减幅度较参考样品降低了3%。

Analysis on The Ageing Mechanism of GaN-based Blue and Green LED by Electrical Stresses

The behavior of the related reliability of InGaN-based blue and green LED chips were investigated with 20, 40, 60 mA constant current stress up to 424 h at room temperature. Under 60 mA constant current stress, the green LED chip showed more prominent optical power degradation at low measuring current levels than high measuring current levels. While, the blue LED chip showed the consistent optical power decrease at different measuring current levels. It should be pointed out that, at high measured current levels (20 mA), blue and green LED chips expressed similar optical degradation (18%) after the aging tests. Meanwhile, the aging stress does not significant affect the forward-bias electrical characteristics of blue and green LED chips, which indicated the similar degradation process in some aging tests. It is believed that the induced defects in blue LED by electrical stress mainly contribute to the nonradiative recombination centers, while in green LED chip the defects contribute to the localized leakage paths rather than the nonradiative recombination centers. Based on the mechanism analysis of blue and green LED, the design of GaN based epitaxial structure was optimized, and the thickness of quantum barrier was reduced to weaken the internal electrical field in the active layer to improve the reliability of LED.