AlGaN基深紫外发光二极管空穴注入效率的提高途径

Hole Injection Efficiency Improvement for AlGaN-Based Deep Ultraviolet Light-Emitting Diodes

目前,发光波长短于360nm的深紫外发光二极管(DUV LEDs)的外量子效率(EQE)普遍低于10%。一方面,基于高AlN组分AlGaN材料量子阱的出光中存在大量的横磁(TM)模式的偏振光,这极大程度上降低了DUV LEDs器件的光提取效率(LEE);另一方面,受限于现阶段AlGaN材料的外延生长水平,DUV LEDs器件的晶体质量普遍比较差,增加了有源区内非辐射复合率,造成DUV LEDs器件内量子效率(IQE)的衰减。除此之外,载流子注入效率也严重影响着DUV LEDs器件的IQE,尤其是空穴注入效率。为此,研究人员开展了大量的研究来提高空穴注入效率,从而改善DUV LEDs器件的EQE。着重总结探讨了近年来提高DUV LEDs器件空穴注入效率的诸多措施,深刻揭示了其中的物理机理,对改善DUV LEDs的器件性能具有重要的意义。

Currently, the external quantum efficiency (EQE) for deep ultraviolet light-emitting diodes (DUV LEDs) with emission wavelengths shorter than 360 nm is generally lower than 10%. On one hand, the transverse-magnetic (TM) polarized light dominates the light emission from the AlN-rich AlGaN based quantum wells, which strongly reduces the light-extraction efficiency (LEE) for DUV LEDs. On the other hand, limited by the current hetero-epitaxial growth technologies for AlGaN materials, the crystal quality for DUV LEDs is still poor, which increases the non-radiative recombination rate in the active region, thereby causing the reduction of the internal quantum efficiency (IQE) for DUV LEDs. Besides, the carrier injection efficiency, especially the hole injection efficiency, also strongly influences the IQE for DUV LEDs. Thus, the researchers have made extensive efforts to increase the hole injection efficiency and thus improve the EQE for DUV LEDs. The recently proposed approaches for the improvement of the hole injection efficiency for DUV LEDs are reviewed and discussed. Moreover, the underlying physical mechanisms are disclosed in the in-depth level. These are important for the improvement of the device performances for DUV LEDs.