利用改善電洞傳導行為降低氮化銦鎵發光二極體效率下降特性之研究

Abstract

本論文中，我們改良傳統氮化銦鎵發光二極體主動層的磊晶結構，以利改善電洞傳導能力來提升氮化銦鎵發光二極體於高電流的發光效率，降低氮化銦鎵發光二極體效率隨外加電流提高而下降之問題。 第一部分，我們設計了漸變銦含量的氮化銦鎵量子侷限層，期望改善電洞傳導能力，使電洞均勻分布在主動層，藉以提升主動層載子發光複合效率。我們先以模擬軟體Advanced Physical Models of Semiconductor Devices (APSYS)最理論計算，並得到較好的結果，接著將實作樣品做電激發光(Electroluminescence, EL)量測，驗證其發光強度於大電流注入下較使用傳統量子侷限層之樣品為佳，並且降低了發光效率在高電流注入下會產生效率下降之情況。 第二部分，我們對第一部分的模擬結果作更進一步的模擬分析，在模擬結構上我們將傳統量子侷限層作選擇性地替換成漸變銦含量的氮化銦鎵量子侷限層，而在模擬結果顯示出單獨只對第六個量子侷限層作漸變銦含量的結構會使的電子與電洞分部更加匹配，進而增加發光二極體發光複合效率，並且比全部使用漸變銦含量的氮化銦鎵量子侷限層發光二極體的效果為佳，也減緩發光效率在高電流注入下會產生效率下降之情況。 第三部分，我們藉由模擬分析探討藍光與綠光發光二極體的差異，在模擬結果顯示出綠光發光二極體的電子電洞分布更較藍光發光二極體的載子分布來得不均勻，並且受到更大的量子侷限史塔克效應(QCSE)更降低了發光複合效率；最後藉由改善電洞傳輸能力來提升綠光發光二極體的發光效率。

In this thesis, we designed the epitaxial structure of InGaN light-emitting diodes (LEDs) to improve the holes transport, which could alleviate the efficiency droop behavior. We first designed a graded-composition quantum barrier (GQB) for c-plane InGaN/GaN LEDs. The simulation results demonstrated that such GQB can effectively enhance the capability of holes transport as well as electrons confinement. Consequently, the LED with GQB grown by metal-organic chemical vapor deposition exhibited lower forward voltage and alleviated the efficiency droop behavior, as compared to conventional LED. Second, we designed LEDs with selective graded-composition multiple quantum barriers (SGQB). The simulation results showed that the SGQB LED with its sixth barrier graded shows improvements in both droop behavior and radiative recombination due to better holes transport and the spatial overlap between holes and electrons. Third, we have investigated the efficiency droop behavior in GaN-based green LEDs and compared with the blue LEDs. We found that the efficiency droop in GaN-based green LEDs is mainly because the over-accumulated holes at the last quantum well as well as the poor hole transport in the active region. Finally, for improving the holes transport, we use the grading indium-composition quantum barriers in green LEDs. As a result, the efficiency droop behavior is alleviated and the light output power in GQB green LEDs is enhanced by 36.3% at 200 mA compared to conventional green LEDs.