漸變式量子井結構用以減緩綠光發光二極體之效率下降與提升量子效率

Abstract

本論文主要探討在綠光發光二極體中使用步階式量子井結構與漸變式量子井結構以達到提升內部量子效率(IQE)與減緩效率下降(Efficiency droop)之目的，因極化效應中壓電極化與自發極化均會使能帶傾斜造成電子電洞波函數分離、電子溢流、電洞注入困難等降低量子效率因素的狀況，本研究工作是改變傳統發光二極體中多量子井結構固定銦含量，換成步階式進而漸變式銦含量的量子井結構來減緩極化效應的影響，再用模擬的方式從能帶圖、波函數、電子電洞濃度分佈等來探討量子效率提升與緩和效率下降的原因。

The effect of gradual indium gallium nitride (InGaN) quantum wells (QWs) on the suppression of efficiency-droop in green light-emitting diodes (LEDs) is numerically investigated. The presented scheme increases the internal quantum efficiency (IQE) by 45.5% at I=20mA and 55.7% at I=100mA, indicating a considerable reduction of efficiency-droop. This improvement is attributable mainly to the use of the gradual InGaN QWs structure that significantly alleviates band bending in the valence band, improving the transport efficiency of injected holes above that of conventional LEDs. The radiative recombination is thus enhanced as the overlap between electron and hole wave functions is increased. Most importantly, the leakage of injected electrons to p-type region is correspondingly reduced, in turn suppressing the efficiency-droop in the LED.