电极结构优化对大功率GaN基发光二极管性能的影响

在台面结构的GaN基发光二极管(LED)里，电流要侧向传输，当尺寸与电流密度加大之后，由于n型GaN层和下限制层的横向电阻不能忽略，造成了横向电流分布不均匀.通过优化电极结构，以减小电流横向传输距离，制作出两种不同电极结构的大功率GaN基倒装LED.通过比较这两种不同电极结构的GaN基倒装大功率LED的电、光性能，发现在350mA正向电流下，插指电极结构的倒装大功率GaN基LED的正向电压为3.35V，比环形插指电极结构的倒装大功率GaN基LED高0.15V.尽管环形插指电极结构GaN基LED的发光面积略小于插指电极结构GaN基LED，但在大电流下，环形插指电极结构倒装GaN基LED的光输出功率比插指电极结构的倒装大功率LED的光输出功率大.并且在大电流下，环形插指电极结构的倒装大功率LED光输出功率饱和速度慢，而插指电极结构的倒装大功率LED光输出功率饱和明显.这说明优化电极结构能提高电流扩展均匀性，减小焦耳热的产生，改善GaN基LED的性能.

Effects of optimized contact scheme on the performance of high-power GaN-based light-emitting diodes

Due to the lateral current transport in the mesa-structure GaN based LEDs，the resistance of the n-type material of the GaN and lower confinement layer is not negligible for large area and high applied current density applieations，which causes the current spreading nonuniformly along the lateral direction. With an optimized contact scheme to reduce the length for the lateral current transport，two different kinds of contact schemes of high-power GaN-based flip-chip LEDs (FCLEDs) are fabricated. It is shown that the forward voltage of this FCLED with interdigitated contact scheme is 3.35V at forward current 350mA，and exceeds that of FCLEDs with optimized ring-shaped interdigitated contact scheme by 0.15V. Although the light emitting area of FCLEDs with optimized ring-shaped interdigitated contact scheme is slightly smaller than that of FCLEDs with interdigitated contact scheme，it is found that the light output from the former is larger than that from the later at higher injection currents. Furthermore，the light output from the FCLEDs with optimized ring-shaped interdigitated contact scheme saturates slowly at higher injection currents as compared to the FCLEDs with interdigitated contact scheme，indicating that the saturation behavior of the FCLEDs with interdigitated contact scheme is more pronounced. It is confirmed that an optimized contact scheme，which leads to the more uniform current spreading，can decrease joule heat generated and considerably improve the electrical and optical characteristics of the FCLEDs.