三五族半導體發光二極體接面溫度之數值模型與特性探討

Abstract

發光二極體(Light-emitting diode, LED)的接面溫度(Junction temperature, TJ)直接且深遠地影響其輸出特性與元件壽命，因此，準確的量測及評估發光二極體之接面溫度是必須且非常重要的。本論文提出一個準確計算氮化銦鎵(InGaN)與磷化鋁鎵銦(AlGaInP) LEDs接面溫度的物理模型，並探討各個相關物理參數，對發光二極體接面溫度的影響。我們發現，發光二極體其順向電壓(Vf)對電流(I)的偏微分，∂Vf /∂I，及對溫度(T)的偏微分，∂Vf /∂T，相互獨立且不相依；因此，我們可將Vf表示為一個接面溫度與注入電流的線性函數。再由穩態下能量守恆，得出光輸出與熱消耗功率之間的平衡關係。最終，我們推導得出發光二極體其注入電流對接面溫度之物理關係式。依據此關係式，本論文進而討論影響LED接面溫度的一些重要物理參數—包含LED之轉換效率(η)、串聯電阻(Rs)以及熱阻(Rth)對接面溫度的影響。 我們發現轉換效率(η)的變化，對於發光二極體的接面溫度只有些微的影響。因此，常見於InGaN LED之效率下降效應(Efficiency-droop effect)，對於接面溫度的影響可以被合理的忽略。此外，元件中 與 的大小，為影響LED接面溫度與注入電流間斜率變化的主因；如此，有效控制磊晶品質以降低元件之串聯電阻，或是使用雷射剝離結合基板接合技術來替換導熱係數較高之基板材料，是有效且直接降低LED接面溫度的方式。 更重要的是，本論文所提出之物理模型，是藉由量測LED的外部特性，即能獲得LED接面溫度與注入電流之關係式。因此，本物理模型，並不侷限於氮化銦鎵與磷化鋁鎵銦化合物半導體，將可廣泛地應用到其他三五族相關半導體元件。The junction temperature of a light-emitting diode (LED) directly and greatly affects its performances. Therefore, the reliable measurement and accurate estimation of the junction temperature of an LED is extremely important. This work proposes an approach for directly determining the dependence of junction temperature on injected currents in InGaN and AlGaInP LEDs. The partial derivatives the forward voltage with respect to injected current (∂Vf /∂I) and junction temperature (∂Vf /∂T) are mutually independent, indicating that the forward voltage of the LED is indeed a linear function of injected current and junction temperature. Further separating the light-output power from the generated heat energy yields the physical dependence of junction temperature on injected current. Various important physical parameters include , and that affect the junction temperature of an LED are also considered and compared. Apparently, the and of the LED dominate the increase in junction temperature. In particular, the increase in the junction temperature with is more serious in the InGaN LED than in the AlGaInP LED, revealing that approaches such as wafer bonding and sapphire lift-off, which reduce the of an InGaN LED are an effective in reducing its junction temperature. More generally, the derivation of junction temperature herein is fundamentally based on the external properties of an LED, and therefore, can be applied to LEDs formed from other III-V compounds.