氮化銦鎵/氮化鎵多重量子井發光二極體之特性與內部量子效率研究

Abstract

本論文中，我們利用有機金屬氣相沉積法成長在不同的藍寶石基板上，前者為成長在圖案化藍寶石基板(Patterned sapphire substrate, PSS)之氮化銦鎵/氮化鎵(InGaN/GaN)多重量子井(Multiple quantum well, MQW)，後者為成長在一般藍寶石基板。我們利用光激發螢光(Photoluminescence, PL)、電激發螢光(Electroluminescence, EL)、以及Advanced Physical Models of Semiconductor Devices (APSYS)模擬軟體等進行樣品的光學與電特性分析。 我們藉由變功率光激發螢光和低溫電激發螢光量測去探討低溫和室溫時，影響氮化銦鎵/氮化鎵多重量子井發光二極體內部量子效率(Internal quantum efficiency, IQE)之物理機制，發現氮化銦鎵/氮化鎵多重量子井發光二極體之內部量子效率會隨著雷射激發功率而變化，主是受到量子井內之非輻射複合中心以及量子井內之量子侷限史塔克效應(Quantum confined Stark effect, QCSE)與能帶填滿效應(Band filling effect)所影響。在本研究中，也利用了理論模型去計算內部量子效率，計算得到的內部量子效率與實驗結果幾乎吻合。 另外由低溫電激發螢光量測，我們發現當在低溫高電流注入時，電洞會因為溫度變化造成的載子濃度以及遷移率下降，造成電洞在量子井中的分布不均勻，且因為電洞的遷移率下降，造成更多的電洞無法有效的注入到量子井中而累積在靠近p-GaN的量子井中，另外也由於量子井中電洞的不足，造成更多的電子會產生溢流現象，導致內部量子效率在高電流下會產生效率遽降的情況。

In this study, we studied two kinds of structures grown by metalorganic chemical vapor deposition (MOCVD). The samples of InGaN/ GaN MQW ultraviolet light emitting diode (UV LED) were grown on c-plane patterned and conventional sapphire substrate. The photoluminescence (PL), low temperature electroluminescence system (LTEL) and Advanced Physical Models of Semiconductor Devices (APSYS) were performed to investigate the optical and electrical properties of the grown samples. This research intends to investigate the physical mechanisms of excitation power and injection current dependent internal quantum efficiency (IQE) in InGaN/GaN MQW LEDs at 15 K and 300 K for PL and 30 K and 300 K for EL. The dependence of the IQE on excitation power density has been observed, we confirmed the variation of IQE with increasing excitation power is due to the coulomb screening of quantum confined Stark effect (QCSE) and band-filling effect in InGaN/GaN QW. Moreover, the nonradiative recombination has to be taken into account at lower excitation power. We also used the theoretical model to calculate the IQE; the calculation of IQE coincides with our experimental results. From the low temperature electroluminescence measurement, the hole concentration distribution is not uniform which can be attributed to the hole mobility decreased at low temperature resulting in hole couldn’t transport to the later QW effectively. Under this condition where thermal generation of holes is insufficient and injected electrons continuously deplete holes, some of the injected electrons reach the p-GaN and exit the system without being able. Consequently, the results verified the EL efficiency droop more rapidly at lower temperature.