功率型GaN基发光二极管芯片表面温度及亮度分布的物理特性研究

The physical characteristic study on luminance uniformity and temperature for power GaN LEDs chip

基于电流连续方程、欧姆定律及定性三维热流传导模型研究发光二极管(LED)芯片的电流密度分布、热量、温度之间的相互交叉关系,进而测试分析GaN基蓝光LED电流扩展效应和亮度分布的关系,认为芯片亮度变化趋势可作为判别电流扩展性能的有效手段.由于芯片表面温度、亮度分布和电流密度之间存在紧密的联结关系,通过测试芯片表面温度或亮度分布就可定性了解器件电流扩展性能,从而为优化电极结构提供一种判定依据.在不同电流和热沉温度下,进一步讨论了电流密度非均匀性和亮度分布的关系,电流密度拥挤将导致芯片局部区域热量堆积,非辐射复合作用增强,限制出射光子数目,因此热量是影响亮度分布的重要因素之一.通过载流子传输机理进一步说明温度影响亮度均匀性的原因,并通过实验说明理论分析的可行性.通过优化电极结构能改善器件的电流扩展效应以及亮度均匀性,对提高大功率LED的可靠性具有重要作用.

In this paper, we study the relationship among current density distribution, heat and temperature based on current continuity equation, ohm law and three-dimensional heat transfer model. The relationship between luminance distribution and current spreading of GaN blue light emitting diode （LED） is studied. Luminance distribution is proved to be an effective method of distinguishing the performance of current spreading. Because of the close relationship among temperature, luminance distribution and current density, a qualitative method of optimizing electrode structure and current spreading is proposed. With different currents and heat sink tem- peratures, the current non-uniformity and the luminance distribution of LED are analyzed. Temperature or current density crowding results in heat accumulation, increase of non-radiative recombination and the restriction of the emitting photons, hence thermal flux is an important factor influencing the luminance distribution. Through cartier transport mechanism, the reason for the temperature influence on luminance distribution is explained. Optimized contact electrode structure can improve current spreading and luminance uniformity, also considerably increase the reliability of high power LED.