在本篇論文中，我們展示了新的串接式綠光發光二極體以應用於塑膠光纖車內通訊，並且具有極高的溫度忍受性(200 ℃)。串接三顆綠光發光二極體的元件能直接藉由汽車的驅動電壓12伏來操作，避免額外串聯電阻造成功率的浪費。藉由在N-contact層與主動區之間增加了一層氮化銦鎵緩衝層，此新的LED和無緩衝層的樣本相較之下有較小的turn on電壓(9.3伏 vs. 11伏 在20 mA)、較大的飽和輸出功率(25.5毫瓦 vs. 22.5毫瓦 在180 mA )、較寬的頻寬 (100 MHz vs. 40 MHz，在定電壓12伏下)，更佳的電流分佈效果，以及高溫下較低的功率退化 (約-0.1 %℃-1)。此元件操作在170mA下即可達到300Mbit/sec的資料傳輸，且在200 ℃下無明顯退化。 此外，為了研究LED的內部載子動力學，我們也開發了新穎的Electrical-Optical pump-probe方法。透過直接注入短脈衝電信號激發，此方法可以直觀地得到樣本的光響應波形，以分析其原始的載子動力學。以此方法分析我們的新元件，我們確認了所觀測到的高電流下效率衰退（efficiency droop）現象主要歸因於歐傑復合效應，且其內部響應時間與串接數無關。We demonstrate a novel type of linear cascade green light-emitting diode (LED) arrays as a light source for in-car or harsh environment plastic optical fiber (POF) communications. To further enhance its dynamic and static performance, an InGaN layer is inserted between an n-type GaN cladding layer and InGaN/GaN multiple quantum wells as an efficient current spreading layer. Compared with the control device without that layer, our three-LED cascade array demonstrates a smaller turn-on voltage (9.3 vs. 11V at 20mA) and a larger output power (25.5mW vs. 22.5mW at 180mA), corresponding to anenhancement of around 31% in wall-plug efficiency. Furthermore, under a constant voltage bias of an in-car battery (12V), our three-LED array exhibits a superior E-O 3-dB bandwidth (100 vs.40MHz) performance to that of the control. Even under high-temperature dynamic operation, we observe that the InGaN insertion layer strongly enhances modulation-speed with negligible degradation of the output power, unlike red resonant-cavity LEDs conventionally used for POF. 200Mbit/sec error-free transmission is achieved at 200℃ which is the highest operation temperature among all the reported high-speed LEDs. For the first time, internal carrier dynamic inside GaN-based green light-emitting-diodes (LEDs) during operation is directly observed by using demonstrated technique; electrical-optical pump-probe. By pumping short electrical pulses (~10ps) into high-speed cascade green LED, we can probe its output optical pulses by use of high-speed photo-receiver circuits. Based on such method, the recombination time constant of carriers can be measured directly without any assumption on recombination process. A high-speed cascade LED structure is adopted in our experiment to eliminate influence of RC-delay time on measured responses. Our measurement result indicates that both single and cascade three-LED structure have the same internal response time due to current continuity. Furthermore, according to measured responses under different temperatures (25℃ to 200℃), the origin of efficiency droop of GaN-based green LED under high bias current density may be attributed to strong non-radiative Auger effect instead of device heating or carrier over-flow.
