高壓發光二極體光電特性以及暖白光效率改善之研究

Abstract

本論文中，我們針對傳統螢光粉轉換之直流藍光發光二極體結構進行改良，成功改善固態照明之市電電壓轉換效率並且提升暖白光之發光效率及品質。 第一部分於氮化銦鎵發光二極體晶片中設計彼此串連之微晶粒結構，藉由最佳化單顆氮化銦鎵晶片之操作電壓以減少與市電之間電壓轉換損失，並透過微發光二極體陣列設計增加晶片上電流分布之均勻性，藉以提升整體白光發光效率，經由理論分析找得最佳化設計後，利用電激發光(Electroluminescence, EL)以及晶片表面之光強分布(Beam View)量測實作樣品，驗證此高壓氮化銦鎵發光二極體晶片發光強度與電流分布確實較傳統晶片佳，並且緩解發光效率於高電流會產生效率驟降的情況。 再者，我們利用氮化銦鎵藍光發光二極體以及磷化鋁銦鎵紅光發光二極體再加上黃色螢光粉實現複合結構之暖白光光源，相較於傳統螢光粉轉換之暖白光發光二極體，利用磷化鋁銦鎵紅光發光二極體取代紅色氮化物螢光粉，成功解決傳統冷白光發光二極體與暖白光發光二極體間之效率落差，更緩解發光效率於高電流會產生效率驟降之情況，此外，透過磷化鋁銦鎵紅光發光二極體之加入與氮化銦鎵藍光發光二極體激發黃色螢光粉之機制達成高演色性(CRI=90)之暖白光源。然而，此複合結構暖白光光源卻存在色溫不穩定之缺點，經由模擬分析後，採用電流補償之機制，有效改善了色溫穩定性，並將色溫穩定常數由0.83提升至0.99。

In this thesis, we designed the hybrid warm white structure of high-voltage light-emitting diodes (HV-LEDs) to reduce the wall plug conversion losses and improve both the warm white efficiency and light quality. First, we designed the series connected micro-diodes array in single chip to form the HV-LEDs which operated at relative low injection current at high forward voltage. The high forward voltage is able to reduce the voltage-conversion loss from wall plug. The simulation results demonstrated that such micro-diodes can effectively enhance the uniformity of current distribution. Consequently, the HV-LEDs with micro-diodes array exhibited higher light output power and lower current crowding ratio measured by the electroluminescence and the beam view separately at high current density, as compared to conventional LED. Second, we demonstrated the hybrid warm white structure with InGaN LEDs, AlGaInP LEDs and yellow phosphor. Different from the conventional full phosphor conversion warm white LEDs, the proposed structure replace the red phosphor by the red AlGaInP LEDs and successfully solve the efficiency gap between cool and warm white LED with an excellent color rendering index (CRI=90). Furthermore, the droop behavior would also be reduced dramatically 18% in the proposed system. However, there is a correlated color temperature (CCT) instability problem observed at different temperatures. The simulation results show that the thermal-dependent intensity drop of red LEDs is the main reason for CCT instability. Thus, the current compensation method is applied and successfully improved the CCT stability factor from 0.83 to 0.99.