利用能帶結構設計改善氮化銦鎵綠光發光二極體之外部量子效率和高電流效率下降現象

Abstract

於本論文中，我們想要改良傳統氮化銦鎵發光二極體主動層之磊晶結構，以改善電洞傳導能力和電子溢流，甚至是降低極化效應來提升氮化銦鎵綠光發光二極體於高電流之發光效率，以及緩解氮化銦鎵綠光發光二極體效率隨外加電流提高而下降之問題。我們的實驗方法是利用模擬軟體Advanced Physical Models of Semiconductor Devices (APSYS)設計結構做理論計算，來分析理論計算出來的能帶圖和載子分佈圖，在確實得到有效的提升後，進而利用Metal-Organic Chemical Vapor Deposition(MOCVD)磊晶，製程出元件，量測元件的光強度與外部量子效率之電特性探討。以下三個部分，分別介紹我所提出在主動層不同位置的結構設計。 第一部分，我們設計漸變銦含量之氮化銦鎵量子能障層，期望改善電洞傳導能力，使電洞均勻分布於主動層，並且藉由銦含量的溶入在量子能障層來降低極化效應來提升主動層載子發光複合效率來改善發光效率於高電流注入下產生效率下降之情況。 第二部分，我們設計漸變銦含量之氮化銦鎵和階梯式漸變銦含量之氮化銦鎵在最後一層量子能障層，期望改善電洞注入能力和降低漏電流效果提升主動層載子數，進而提升載子發光複合效率來改善發光效率於高電流注入下產生效率下降之情況。 第三部分，我們設計四元氮化鋁銦鎵和氮化鎵的超晶格結構(super-lattice)在電子阻擋層上，期望改善電洞注入能力和降低漏電流效果，來增加主動層載子數，進而提升載子發光複合效率改善發光效率於高電流注入下產生效率下降之情況。

In this thesis, we want to design the epitaxial structure of InGaN-based green light-emitting diodes (LEDs) to improve the holes transport, electron leakage, and polarization field which could enhance the external quantum efficiency and alleviate the efficiency droop behavior. In our experiment ways, we used Advanced Physical Models of Semiconductor Devices (APSYS) simulation software to design our structure and calculate the band diagram and carrier distribution. From the simulation have a good result, we further fabricate the green LEDs sample with design structure by Metal-Organic Chemical Vapor Deposition(MOCVD) and measure the electrical characteristics by Electroluminescence (EL) instrument. The following of three parts are our design structure introduction and discussion. First, we designed a Indium graded-composition quantum barrier (GQB) with indium composition decreasing along the (0001) direction from 7% to 0% for c-plane InGaN/GaN green LEDs. The simulation results demonstrated that GQB can effectively enhance the transport capability of holes as well as electrics confinement and reduce polarization field. Consequently, the GQB LEDs have better external quantum efficiency and alleviated the efficiency droop behavior as compared with conventional LED by EL measurement. Second, we designed a Indium graded-composition last barrier (GLB) and Step Indium composition Last barrier(Step LB) with indium composition increasing along the (0001) direction from 0% to 5% for c-plane InGaN/GaN green LED. The simulation results showed that the GLB and Step LB structure can improve the effective barrier high of electrons and holes and reduce the electrics field in the last well. As a result, the holes transport in MQWs was enhanced and confine more carrier in the well to increase the radiative recombination efficiency at high current density. Consequently, the GLB and Step LB LEDs have better external quantum efficiency and alleviated the efficiency droop behavior as compared with conventional LED by EL measurement. Third, we have designed AlInGaN/GaN super-lattice electrics blocking layer for c-plane InGaN/GaN green LED. The simulation results showed that the AlInGaN/GaN SL EBL can reduce the electrics field in the last GaN barrier and improve the effective barrier high of electrons and holes. As a result, the holes transport in MQWs was enhanced and confine more carrier in the well to increase the radiative recombination efficiency at high current density. Consequently, the AlInGaN/GaN SL EBL have better external quantum efficiency and alleviated the efficiency droop behavior as compared with conventional LED by EL measurement.