Enhancement of the Modulation Bandwidth of a light-emitting Diode through Surface Plasmon Coupling

我們透過微縮元件面積、減少主動層厚度，並將表面電漿子耦合效應應用在藍、綠色發光二極體上以提高元件的調變頻寬。本論文中，我們比較三種不同的表面結構，分別為p型氮化鎵、利用氧化鎵鋅當電流擴散層和有表面電漿子耦合效應的隨機分佈銀奈米顆粒的效果，其中具有表面電漿子耦合效應，而元件半徑10微米的單層量子井，其藍色發光二極體測得的頻寬為目前可見光波段最高紀錄528.8 MHz。理論上當發光二極體的RC時間常數越小，可量得越高的頻寬，然而從實驗得知，當RC時間常數小於0.2奈秒時此效果會趨於飽和。從調製頻寬對注入電流密度和載子衰退時間的相依性來看，可證實調變頻寬與一特定時間常數成反比，而此時間常數與載子衰退率和注入電流密度有關。The increases of modulation bandwidth by reducing mesa size, decreasing active layer thickness, and inducing surface plasmon (SP) coupling in blue- and green-emitting light-emitting diodes (LEDs) are illustrated. The results are demonstrated by comparing three different LED surface structures, including bare p-type surface, GaZnO current spreading layer, and Ag nanoparticles (NPs) for inducing SP coupling. In a single-quantum-well, blue-emitting LED with a circular mesa of 10 m in radius, SP coupling results in a modulation bandwidth of 528.8 MHz, which is believed to be the record-high level in visible range. A smaller RC time constant can lead to a higher modulation bandwidth. However, when the RC time constant is smaller than ~0.2 ns, its effect on modulation bandwidth saturates. The dependencies of modulation bandwidth on injected current density and carrier decay time confirm that the modulation bandwidth is essentially inversely proportional to a time constant, which is inversely proportional to the square-root of carrier decay rate and injected current density