近年來隨著科技的進步,智慧型手機、電動車的普及,能源問題以及科技產品對於功率元件性能得需求越來越高。以至於一般矽(Si)基板所製作的功率元件已無法滿足人們的需求。隨之而來的是第三代半導體的蓬勃發展，其中應用於功率元件的材料又以SiC(碳化矽)基板最為普遍。然而，相較於矽(Si)和SiC(碳化矽)基板，氮化鎵(GaN)擁有更大的能隙、電子遷移率以及在大電場時有較大的電子飽和速度，能夠實現較高的崩潰電壓，以及較小的導通電阻更適合應用於高速、高功率的元件上。而以二極體元件結構來說，垂直式結構相較於水平式結構能夠以較小的面積實現較大的電流，即是有更大的電流密度。另外由於漂移層(drift layer)的氮化鎵直接生長於氮化鎵基板上，能夠將缺陷密度控制在小於106cm-2,也因此有較小的介面應力,預期元件亦有較好的低頻雜訊特性。本論文將針對垂直式GaN-on-GaN進行元件光罩設計以及元件製作，接著我們針對元件DC特性、崩潰電壓進行量測並且與其他參考的研究論文進行規格比較，最後我們會量測元件低頻雜訊並且藉由分析低頻雜訊特性找到GaN-on-GaN 基板內的缺陷的啟動能(activation energy),進而得知不同缺陷所在的能階,作為增進垂直式元件表現的一項參考指標。

In recent years, with the advancement of technology, the popularity of smart phones and electric cars, energy issues and technology products have become more and more demanding in terms of power device performance. As a result, power devices made of silicon (Si) substrates can no longer meet the needs of people. Subsequently, the third generation of semiconductors is booming, and SiC (silicon carbide) substrates are the most common material used for power devices.
　　However, compared to silicon (Si) and SiC (silicon carbide) substrates, gallium nitride (GaN) has a larger energy gap, higher electron mobility, and a higher electron saturation velocity at large electric fields, enabling higher breakdown voltages and lower on-resistance for high speed, high power devices.
　　In terms of the diode structure, the vertical structure can achieve a higher current density with a smaller area than the horizontal structure. In addition, the drift layer is grown directly on the GaN substrate, keeping the defect density to be less than 106 cm-2, resulting in lower interface stresses and better low-frequency noise characteristics.
　　In this thesis, we will use the vertical GaN-on-GaN structure to realize the diodes. First, we will design the photomask and fabricate the device, then we will measure the DC characteristics and breakdown voltage of the device and compare the specifications with other reference papers, finally we will measure the low-frequency noise of the device and find the activation energy of the defects in the GaN on GaN substrate by analyzing the low frequency noise characteristics, then we will know the energy level of different defects, which will be a useful index for the further improvement of vertical GaN-on-GaN devices.

Content

中文摘要 3
Abstract 4
Content 5
List of Figure 7
List of table 11
CHAPTER 1 13
INTRODUCTION 13
1.1 Motivation 13
1.2 Thesis Organization 15
CHAPTER 2 16
CHARACTERISTICS OF GALLIUM NITRIDE MATERIALS AND DEVICES 16
2.1 Basic Characteristics of Gallium Nitride Materials 16
2.1.1 Critical electric field and on-resistance 17
2.2 GaN Schottky Barrier Diode introduction 20
2.2.1 Characteristics GaN Schottky Barrier Diode 20
2.2.2 Schottky barrier diode development and applications 23
2.3 Literature review 26
2.3.1 GaN Trench MIS Barrier Schottky Rectifiers with implanted field rings[25] 26
2.3.2 Vertical GaN-on-GaN Schottky Barrier Diodes with Multi-Floating Metal Rings [22] 27
2.3.3 Vertical GaN-on-GaN schottky barrier diode with nitridation-based termination [23] 29
2.4 Summary 30
CHAPTER 3 31
DEVICE DESIGN AND PROCESS STEPS 31
3.1 Device design 31
3.2 Device Process Steps 33
3.2.1 Photolithography 34
3.2.2 Device process flow 35
3.3 Summary 41
CHAPTER 4 43
MEASUREMENT METHODS AND RESULTS 43
4.1 DC measurement method 43
4.1.1 Ohmic contact measurement 44
4.1.2 Ohmic contact measurement 48
4.2 Low-frequency noise measurement method 49
4.3 Measurement Results 51
4.3.1 Diode forward bias characteristic 51
4.3.2 Diode Reverse bias characteristic 62
4.3.3 Low-frequency noise characteristic 72
4.4 Chapter Summary 83
CHAPTER 5 85
CONCLUSION AND FUTURE WORK 85
5.1 Conclusion 85
5.2 Future work 86
References 87

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