使用模擬探討氮化鎵發光二極體及鍺鰭式電晶體效能的改進

Abstract

本論文中基於先端光電元件的開發困難，因此提出方法來改善並提高光電特性和電子元件性能，包括氮化鎵(GaN)發光二極體(LED)和鍺鰭式電晶體(Ge FinFET)。 本論文使用先進半導體元件物理模型模擬軟體(Advanced Physical Models of Semiconductor Devices, APSYS)模擬氮化鎵材料的特性、並使用其物理參數以及極化場的計算來模擬發光二極體結構並設計出可改善效能的結構設計。此外，我們使用3D-DDCC模擬軟體來研究探討鍺鰭式電晶體特性，並以理論模型探討其不理想機制。 於本篇論文中的第一部分，由於氮化鎵磊晶層與矽基板之間存在巨大的晶格常數和熱膨脹係數不匹配，所以在矽基板上很難得到高品質的氮化鎵薄膜，且晶格不匹配導致更高的應力場使得量子侷限史塔克效應產生的效率下降更為嚴重。本章中藉由模擬與實驗研究改變量子能障厚度，減少量子能障厚度可以降低量子井內的極化電場、改善電洞傳導能力與電子溢流，並減緩發光效率於高電流注入下產生效率下降之問題。 第二部分中的氮化鎵近紫外發光二極體可以應用於紫外線光源、生物醫學，紫外光固化和光觸媒應用於水及空氣的淨化等，目前已經被廣泛地研究與討論。但由於近紫外光發光二極體量子井內銦含量很少，缺少由銦局域態致使載子侷限不佳，導致發光復合效率會比藍光與綠光氮化銦鎵發光二極體來得差，除此之外，電子溢流與電洞傳輸困難也是發光效率不好的原因。本章將從模擬來設計超晶格結構電子阻擋層與研究改變超晶格結構的厚度對於氮化銦鎵近紫外光發光二極體之光性與電性影響，並提出可改善其效能之結構設計。 第三部分討論電晶體尺寸持續微縮下，其短通道效應越趨嚴重，鰭式電晶體因具有三面立體式之閘極結構，可增加閘極對通道的控制能力改善短通道效應。此外，鍺比矽擁有更高的電子與電洞遷移率，被視為有很更大潛力能夠取代矽通道電晶體，結合鍺的高遷移率與鰭式電晶體結構的優點可以提升晶片效能與省電效益。然而，鍺因為其氧化物品質的不穩定使得介面態密度很高，且鍺的低能隙特性容易在高電場下產生能帶間穿隧造成漏電流，這些原因使得鍺鰭式電晶體的效能受到限制，本章將藉由模擬來研究介面態與帶間穿隧漏電流對鍺鰭式電晶體效能的影響。

In this thesis, due to the development of the advanced optoelectronic devices are difficult, hence, we propose ways to improve and enhance the performance of optoelectronic devices, including gallium nitride (GaN) light-emitting diodes (LEDs) and germanium fin field effect transistors (Ge FinFETs). The Advanced Physical Models of Semiconductor Devices (APSYS) simulation software was employed to simulate GaN-based LEDs, the physical models including GaN-based material characteristics, polarization field and etc. The 3D-DDCC simulation software was introduced to preview and study characteristics of Ge FinFETs. In the first part of this thesis, since there is a large mismatch of lattice constant and thermal expansion coefficient between gallium nitride and silicon substrate, the droop effect becomes more serious. In this chapter, we investigated and modified the thickness of quantum barriers by simulation and experiment. Reducing the thickness of the quantum barriers can reduce the polarization field of quantum wells, and improve electron overflow and hole transport ability. Therefore, the efficiency droop could be improved. In the second part of this thesis, the GaN-based near-UV light-emitting diodes have been discussed. Due to lack of indium localized states in the quantum wells, the carriers confinement are poor, resulting in poor quantum efficiency as compared with blue and green light-emitting diode. In addition, electron overflow and poor hole transport ability are also the reasons of poor quantum efficiency. In this chapter, we designed superlattice structure of the electron blocking layer with modifying the thickness of the superlattice for near ultraviolet light-emitting diode. Performance enhancement in such of designs were demonstrated by simulations and experiments. In the third part of this thesis, the Ge FinFET structure could enhance the device performance and reduce power consumption due to its high mobility for holes and also shows the reduction of short channel effect by Fin structure. In this chapter, we study on the nature of interface trap states in the Ge band gap and small band induced BTBT leakage, which influence the performance of Ge FinFETs.