以有限元素法分析高功率發光二極體的電性和散熱問題

Abstract

氮化銦鎵/氮化鎵發光二極體提供了許多重要的發光元件給人類 生活上使用。這些元件在低注入功率下有著很高的效率以及生命 期，但是到目前為止，在高注入的情況下，整個元件的表現反而是 下降的。電流擴佈和熱的消散是在高注入下，表現下降的主要原 因。在本篇論文中，我們發展了一套三維有限元素法來檢驗熱的產 生與消散以及二維有限元素法之帕松和漂移-擴散方程來分析電流擴 佈。就我們所知，界面溫度在發光二極體裏扮演著很重要的角色， 它不只可以影響元件的效率，它還會影響出光的性質。因此，在本 篇論文裡會討論不同結構下的發光二極體晶片及封裝對散熱的影 響，以及藉由特別設計的發光二極體來改變電流流向。我們可以發 現在晶片或是封裝裡，使用較高熱導係數的材料會有著比較好的散 熱效果，特別是當這個材料靠近熱源區的時候。再者，當晶片與底 部散熱片間的材料層數越少時，散熱效果會變得更好。對於傳統發 光二極體和離子佈植發光二極體的改變電流方向的結果也會在本篇 論文裡呈現。我們的模擬結果顯示藉由元件的設計來調整電流流向 可以讓元件的表現變得更好。

InGaN/GaN LEDs offer important lighting devices for human livings. These devices have high efficiency and lifetimes at low injection power but so far show degradation under high injection conditions. Current spreading and heat dissipation are key reasons for degradation under high power operation. In this thesis, we have developed a three-dimensional (3-D) finite element method (FEM) to examine the heat generation and dissipation and a two-dimensional (2D) Finite element Poisson and drift-diffusion solver for the analysis of current spreading. As we know, the junction temperature plays an important role to the performance of the LED, and it will influence the optical performance. Therefore, the discussion of different structures for LED chips and packages will be considered in this thesis. We have examined how current flow can be altered by a careful design of the LEDs. We can find that higher thermal conductivity of the materials used in the chip or package can lead to a better heat dissipation especially in it near the heat source region. Also, when the number of layers between the chip and bottom heat sink are becoming less, the effect of heat dissipation can be promoted. Results for a conventional LED and a LED with ion-implantation to improve current flow are also presented. Our simulations show that with better design of the current spreading can improve the device operation.