大功率GaN基发光二极管的电流扩展效应及电极结构优化研究

定性分析了GaN基LED的电流扩展效应，发现电流密度和电流横向扩展的有效长度对电流均匀扩展有很大影响.基于此，对GaN基大功率LED提出了优化的电极结构，以减缓电流拥挤效应，降低器件串联电阻.通过用红外热像仪测量器件表面的温度分布，发现具有优化的环形插指电极结构的GaN基大功率LED表面温度分布比较均匀，证明芯片接触处电流扩展均匀，局部电流密度降低，减小了焦耳热的产生，增强了器件的可靠性.

Research on effects of current spreading and optimized contact scheme for high-power GaN-based light-emitting diodes

GaN-based light-emitting diodes (LEDs) grown on sapphire substrate have current transport along the lateral direction due to the insulating nature of the substrate, and the anode and cathode contacts are in a side-by-side configuration. The resistance of the n-type material of the GaN and the lower confinement layer is not negligible, which causes the current to crowd near the edge of the n-contact pad. The current crowding problems will become more severe for large area and high power devices. In this paper, the current spreading effect is qualitatively analyzed. The applied current density and the effective length of the lateral current transport are found to have a considerable effect on the uniform current spreading. Based on these findings, an optimized contact scheme of high-power GaN-based LEDs is proposed to alleviate current crowding effect and reduce the series resistance of the devices. It is clearly shown that the high-power GaN-based flip-chip LEDs with optimized ring-shape interdigitated contact scheme have a relatively uniform temperature distribution by measuring the surface temperature distribution of the device with infrared thermal imaging system. It is confirmed that the current distributes more uniformly over the contact, and current densities in a localized region of the device are reduced, which can decrease the joule heat generated and improve the reliability of the GaN-based LED.