臺灣博碩士論文加值系統

　　在本論文中，藉由即時偵測系統以及量測分析，我們可以有系統的研究探討磊晶品質以及特性分析。我們並且能夠成功的製作出氮化鋁鎵與氮化鎵異質結構場效電晶體，其主要是利用其介面所形成的二維電子雲(2DEG)與壓電效應(piezoelectric)。對於新型態的氮化鎵與氮化銦鎵二維電子雲異質結構場效電晶體也有進一步的探討。另外我們使用了再成長（regrowth）的方式來改善我們的元件。

　　利用有機金屬法成長的電晶體，摻鎂(Mg)高阻抗絕緣層提供良好的電晶體關閉特性。我們比較了兩組不同的歐姆接觸之合金金屬，鉻/鋁以及鈦/鋁/鈦/金，藉由傳輸線模型可得知使用鈦/鋁/鈦/金的元件會有比較佳的直流與高頻特性。元件顯示了很低的閘極漏電流以及很高的崩潰電壓（> -100 V）。最後我們更可以藉由製程的改善以及閘極線寬的縮小，大幅的提升直流及高頻特性。另一方面，我們使用了表面鍍上氧化層的技術，使得電流衰退現象幾乎不再出現。

　　由於氮化銦（鎵）材料在理論特性上都比氮化鎵以及氮化鋁鎵來得好，所以我們嘗試成長新穎的氮化鎵與氮化銦鎵異質結構場效電晶體，我們更進一步的探討有無鎂摻雜的電流阻絕層以及在其上的無摻雜氮化鎵緩衝層對元件特性的影響，最終跟文獻上的結果相比，我們獲得了很好的元件特性。

　　我們使用不同偏角度的藍寶石基板成長異質結構場效電晶體元件，可以發現這種方法可以有效的改善其缺陷與差排的密度。再成長方式的磊晶，我們在研究中發現可以結合兩種成長技術優點，在有機金屬氣相磊晶系統成長的氮化鎵基板上利用分子束磊晶法成長出高品質的二維電子雲，並且能夠擁有平坦的表面。如此的磊晶技術成長，我們可以獲得比傳統純粹使用有機金屬氣相磊晶系統或是分子數磊晶成長系統還好的直流及高頻特性。

　　In this dissertation, the growth and characterization of nitride-based epilayers have been systematically studied by using in-situ reflectance and ex-situ measurements. We have also successfully fabricated the AlxGa1-xN/GaN 2-dimentional electron gas (2DEG) heterostructure field effect transistors (HFETs), novel GaN/InxGa1-xN 2DEG HFETs and improved AlxGa1-xN/GaN 2DEG HFETs by introducing regrowth technique.

　　For AlxGa1-xN/GaN 2DEG heterostructure field effect transistors (HFETs), a high quality AlGaN/GaN 2DEG heterostructure on a semi-insulating current blocking layer by using bis-cyclopentadienyly magnesium (Cp2Mg) doping process grown by MOVPE system have successfully fabricated. We use two different types of alloy for ohmic contact metals, Cr/Al and Ti/Al/Ti/Au. As the result of getting lower contact resistance and specific contact resistance by using CTLM model , so we choose Ti/Al/Ti/Au for Source-Drain contacts to obtain better HFET devices electrical characteristics such as gmmax 、IDSmax than using Cr/Al for metal contacts. The ohmic contact on the high bandgap AlGaN and sheet carrier densities in 2DEG affected the DC and RF electrical properties in HFETs. The HFET devices show small gate leakage current of few micro ampere levels at VGS = -20 V and the breakdown voltage is more than -100 V. The DC and RF characteristics of AlGaN/GaN 2DEG are also improved by using optimizing process techniques. We also demonstrate a surface passivation technique to suppress the drain current collapse effect of AlxGa1-xN/GaN 2DEG HFETs.

　　Novel structure of GaN/ InxGa1-xN 2DEG HFETs have also been grown by MOVPE system and fabricated. The In(Ga)N epilayers have good potential to be the materials for high mobility and high frequency devices based on its theoretical limits. We compare the device structure with and without the Mg-doped current blocking layer and it is shown that the isolation layer is necessary for our 2DEG structure. Further, we demonstrate an improvement of device characteristics by introducing un-GaN buffer layer on top of Mg-doped current blocking layer. We achieve a better DC performance than the previous work of literature.

　　Moreover, we demonstrate a new technique of growing HFETs on vicinal sapphire substrates. These off-axis substrates are proved to reduce the threading dislocations (TDs) of our epilayers. The regrowth technique has been studied. The high quality AlGaN/GaN 2DEG epilayers grown by ammonia-MBE system on the MOVPE templates are successfully fabricated. We also significantly improve the surface smoothness, and consequently improve electrical characteristics on MOVPE templates by ammonia-MBE system. The results of regrowth technique are better than the devices which are either completely grown by MOVPE system or completely grown by ammonia-MBE system.

Abstract (In Chinese)....................................................... i
Abstract (In English)..................................................... iii
Acknowledge................................................................ vi
Contents................................................................. viii
Table Captions.............................................................. x
Figure Captions............................................................ xi


CHAPTER 1 Introduction
1.1 The Background of Research on III-V Nitrides............................ 1
1.2 Overview of This Dissertation........................................... 4
References.................................................................. 6

CHAPTER 2 Introduction of Metalorganic Vapor Phase Epitaxy System and Growth Characterization
2.1 Introduction of Metalorganic Vapor Phase Epitaxy (MOVPE) System........ 11
2.2 The In-situ Reflectance Monitoring System of Growing III-Nitride Related Materials by MOVPE System.................................................. 16
2.3 The Characteristics of III-Nitride Related Materials Epitaxial Growth by MOVPE System............................................................... 18
References................................................................. 22

CHAPTER 3 Novel Growth of AlGaN/GaN 2DEG Heterostructure Field Effect Transistors (HFET) Structure and Device Characterization
3.1 Introduction of Growing AlGaN/GaN 2DEG Heterostructure Field Effect Transistors Grown by MOVPE System.......................................... 40
3.2 Fabrication of AlGaN/GaN 2DEG Heterostructure Field Effect Transistor Devices Grown by MOVPE System.............................................. 43
3.3 Characteristics of AlGaN/GaN 2DEG Heterostructure Field Effect Transistor Devices Grown by MOVPE System and The Influence of Oxide Passivation on AlGaN/GaN 2DEG HFETs Grown by photo-CVD.................................... 48
References................................................................. 53

CHAPTER 4 Growth and Fabrication of GaN/InGaN 2DEG Heterostructure Field Effect Transistors Structure and Device Characterization
4.1 Introduction of Growing GaN/InGaN 2DEG Heterostructure Field Effect Transistors by MOVPE System................................................ 91
4.2 Study of Growing GaN/InGaN 2DEG Heterostructure Field Effect Transistors by Introducing Mg-doped GaN Current Blocking Layer......................... 93
4.3 Novel Fabrication and Characteristics of GaN/InGaN 2DEG Heterostructure Field Effect Transistors Devices Grown by MOVPE System..................... 95
References................................................................ 101

CHAPTER 5 The Vicinal Sapphire Substrates and Different Regrowth Methods Influences of AlGaN/GaN 2DEG HFETs Structure
5.1 The Characteristics of AlGaN/GaN 2DEG HFETs Grown on Vicinal Sapphire Substrates by MOVPE System................................................ 127
5.2 Introducing of Ammonia-MBE System and The Characteristics of AlGaN/GaN 2DEG HFETs Grown by MOVPE System on ammonia-MBE Substrates................ 132
5.3 The Process and Characteristics of Regrowth AlGaN/GaN 2DEG HFETs Devices Grown by ammonia-MBE System on MOVPE Substrates........................... 135
References................................................................ 141

CHAPTER 6 Conclusion and Future Prospect................................. 171

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