有機金屬氣相磊晶氮化合物緩衝層及深紫外光與綠光波段光電特性之開發研究

The development of nitride-based buffer layer and deep ultraviolet and green band photoelectric properties by metal-organic vapor phase epitaxy

劉宗諺(Tsung-Yen Liu)

指導教授 ： 管傑雄

國立臺灣大學/電機資訊學院/光電工程學研究所/博士(2021年)

https://doi.org/10.6342/NTU202100877

摘要

磊晶為半導體光電元件不可或缺的技術。目前在高效率氮化銦鎵藍、綠光雷射二極體磊晶工藝上，需要好的氮化鎵基板，但因在高溫下氮的飽和蒸汽壓很高，現今的拉單晶技術無法做到。故現今皆是使用HVPE-權衡下之獨立式氮化鎵基板(Free-Standing GaN substrate)。本研究發現在使用此基板下做氮化鎵MOCVD同質磊晶時，因氮化鎵基板殘存的應力及材料品質，為了尋找低缺陷密度、熱力學穩定的氮化鎵磊晶層，我們發現磊晶的成長速率對此表面的品質影響頗大，在相同成長溫度下以較高的成長速率可以提昇氮化鎵磊晶品質以及更好表面的型態。第二部分在氮化鋁鎵 (AlGaN)異質接面磊晶中，我們克服了與AlGaN深紫外光發光二極體磊晶相關的幾個關鍵生長問題。在氮化鋁 (AlN)表面微米厚的AlGaN層中觀察到不規則的錯位聚集以及火山口深坑形貌。在AlGaN層和AlN層之間插入超晶格過渡層後，應力誘導的形貌和缺陷得到抑制，而主動區的缺陷發光是由於三族空缺相關的氧淺施主和深受主的輻射複合控制的，在優化生長條件和减少生長中斷後，藍光波段的寄生發光强度被抑制了95%。最後，在氮化銦鎵研究中提出了全新的思維，追求可得到高成分銦且高品質的InGaN最理想的解決方案，為了得到高成分的銦而犧牲材料中最重要之主動層的磊晶品質，無法真正達到元件的理想特性。長久以來一直研究如何突破高In成分的InGaN只能低溫成長的宿命，就磊晶技術而言成長溫度越高，原子的移動長度(migration length)更大，就更有機會找到可以使電子鍵結後能量降的更低的鍵結位置，可以得到更好的磊晶品質。我們提出可使氮化銦鎵材料去蕪補菁的淬火技術，在磊晶成長InGaN之後，我們升高反應腔溫度並通入銦前驅物，把In-N的弱鍵加速趕走的同時，藉由In-N的再鍵結，可在更高的溫度下維持高銦成分及更好品質的的氮化銦鎵。

關鍵字

有機金屬氣相磊晶 ； 氮化鎵 ； 氮化鋁鎵 ； 氮化銦鎵 ； 深紫外光發光二極體 ； 綠光發光二極體

並列摘要

Epitaxy is an indispensable technology for semiconductor optoelectronic devices. At present, good GaN substrate is needed for high efficiency InGaN Blue and green laser diode epitaxy. However, due to the high saturated vapor pressure of nitrogen at high temperature, the current single crystal pulling technology cannot achieve it. So nowadays, HVPE free-standing GaN substrate is a trade-off product. In this study, we found that the residual stress and material quality of GaN substrate will be affected when GaN MOCVD homo-epitaxy is performed on free-standing GaN substrate. In order to find a low defect density and thermodynamically stable Gan epitaxial layer, we found that the growth rate of epitaxial layer has a great influence on the surface quality. At the same growth temperature, higher growth rate can improve the quality of Gan epitaxial layer and better surface morphology. In the second part, we overcome several key growth problems related to AlGaN deep UV LED epitaxy in AlGaN heterojunction epitaxy. Irregular-shaped pits with dislocation clusters and volcano morphology were observed in micron-thick layers of AlGaN on AlN. The strain-induced morphology and defects were suppressed after the insertion of superlattice transition layers between the AlGaN and AlN layers. The defect luminescence in the active region was governed by radiative recombination through the oxygen shallow donors and deep acceptors related to III-vacancies. After optimization of the growth conditions and a decrease in growth interruption, the intensity of the parasitic blue-band emission was suppressed by up to 95%. Finally, a new idea is put forward in the research of InGaN, which pursues the most ideal solution to obtain high composition indium and high quality InGaN. In order to obtain high composition indium, the epitaxial quality of the most important active layer in the material is sacrificed, which cannot really achieve the ideal characteristics of the device. For a long time, we have been studying how to break through the fatalism that InGaN with high In content can only grow at low temperature. As far as the epitaxial technology is concerned, the higher the growth temperature is, the larger the migration length of atoms is, and there is a better chance to find a bonding site that can reduce the energy after electron bonding, so as to obtain better epitaxial quality. We propose a refined temper fire treatment technique. After epitaxial growth of InGaN, we increase the temperature of the reaction chamber and introduce In precursor to drive away the weak bond of In-N. at the same time, by In-N re-bonding, we can maintain high indium content and better quality of InGaN at higher temperature.

並列關鍵字

Metal-organic vapor phase epitaxy ； Gallium nitride ； Aluminum gallium nitride ； Indium gallium nitride ； Deep ultraviolet light emitting diodes ； Green light emitting diodes

參考文獻

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