以模型化方式探討氮化鎵藍、綠光發光二極體效率下降之原因

Abstract

在本論文中，我們分別探討了蕭特基-瑞德-霍爾復合、輻射復合、歐傑復合、有效主動層體積與漏電流對藍光發光二極體效率下降的影響。經由模型的分析可知，提升輻射復合在總復合當中的比例，有助於提升外部量子效率峰值與改善效率下降現象。此外有效主動層體積的下降雖然不改變外部量子效率峰值，卻會使效率下降隨電流上升而嚴重地惡化。小的有效主動層體積同時讓原本在高電流密度才能凸顯作用的漏電流，變得在低電流密度即可顯現其對外部量子效率的影響。 最後，我們針對所量測到藍、綠光發光二極體外部量子效率曲線的差異加以解釋。我們發現差異主要來自於小能隙綠光發光二極體有較大的歐傑復合係數，同時銦原子集結嚴重造成波函數重疊下降也導致有效主動層體積較藍光發光二極體小。不論藍、綠光發光二極體，在正常情況下，漏電流佔總電流的比例皆不到百分之一，故能排除漏電流是引起效率下降的主因。

In this thesis, we use a model to investigate the influence of Shockley-Read-Hall recombination, radiative recombination, Auger recombination, effective volume, and leakage current on efficiency droop in blue light emitting diodes (LEDs). We find that increasing the ratio of radiative recombination to overall recombination rate, can improve the peak value of the external quantum efficiency (EQE) and alleviate the efficiency droop phenomenon. Besides, the decrease in the effective volume does not change the EQE peak value, but severely deteriorates the efficiency droop. We also find that a small effective volume may cause a significant leakage current at a low total current density. We also study reasons for the difference in measured EQE curves between blue and green LEDs. We find that the efficiency droops more significantly for green LEDs than blue ones, due to a larger Auger coefficient and a smaller effective volume which results from indium aggregation or other factors causing more incomplete wave function overlap. Moreover, for both blue and green LEDs, the ratio of the leakage current to the total current is less than one percent in a normal operating current level. This indicates that the leakage current can be excluded from the origin of efficiency droop.