於此研究中，將於氮化鎵基板上以有機化學氣相沉積法(MOCVD)和氫化物氣相磊晶法(HVPE)沉積出高功率p-i-n二極體結構，用以製作出垂直式氮化鎵p-i-n二極體。在順向偏壓操作下，當電壓到達一定大小時會由低階注入轉為高階注入使得本質層產生電壓調變的現象，而使順向串聯電阻大幅下降而使元件有較低的導通電阻。當施以一逆向偏壓時，因為p-i-n結構中本質層的設計，而使得元件逆向可以承受高電壓。
元件設計相同之本質層厚度但改變本質層之濃度分布來製成元件，順向偏壓下，整體本質層不去做參雜之磊晶結構依完全相同之製成手法和相同元件結構設計下，順偏電性有導通不順以及順向導通特徵電阻較大之特性，整體本質層去做部分參雜部分不參雜之磊晶結構，順偏電性有著顯著的提升導通特徵電阻大幅的下降，且為了更進一步提升順偏導通特性，表面雷射退火技術可以進一步活化表面P型氮化鎵半導體參雜離子而使濃度提升進一步使順偏導通特徵電阻下降而得到更好的順偏特性。逆偏特性方面，順偏特性和逆偏特性是相對的，越好的逆偏特性相對的順偏特性也會不好，因此為了改善逆偏特性而使用了兩種不同的P接觸金屬，提升些微順偏電阻來使逆偏崩潰大幅提升。此外也利用感應耦合電漿體反應離子蝕刻(ICP-RIE)技術蝕刻出不同的側壁形狀藉此降低側壁電場使漏電流下降，並且進一步提升崩潰電壓。此外也有使用離子佈植的方式作為元件隔離的方法，此法可以使元件沒有感應耦合電漿體反應離子蝕刻(ICP-RIE)所會產生的側壁漏電的現象故此預期可以獲得更高的崩潰電壓。最後結合所有技術應用於本質層20微米其中5微米濃度1×1015 cm-3、15微米濃度1×1016 cm-3之磊晶結構得到最低特徵導通電阻0.61 mΩ-cm2及超過2870 V的崩潰電壓，而得到最佳巴利加值(Baliga’s Figure of Merit, BFOM)大於13.5 GW/cm2。

In this study, high power GaN p-i-n epitaxy structure was deposited on free-standing GaN substrate by organic chemical vapor deposition (MOCVD) and Hydride Vapor Phase Epitaxy (HVPE) to fabricate vertical p-i-n diodes. During forward bias operation, increasing voltage would promote intrinsic layer from low level injection into high level injection and result in conductivity modulation. Hence, the series resistance would decrease substantially and the conductive specific contact resistance would decrease identically. During reverse bias operation, because of the intrinsic layer in p-i-n structure, device could afford high voltage.
By using different concentration and identical intrinsic layer thickness fabricates the device. In forward characteristic, intrinsic layer with non-doping was bad forward bias characteristic and higher specific contact resistance. However, intrinsic layer with partially slight doping was significantly improve in forward characteristic and specific contact resistance. In order to more decrease specific contact resistance, using laser annealing could activate the p-type GaN to increase the p-type GaN concentration resulting in lower specific contact resistance and better device characteristic. Otherwise, forward characteristic and reverse characteristic are relative. Therefore, better forward characteristic means worse reverse characteristic. To increase blocking voltage, two type of P-contact metal were chosen. By slightly increasing specific contact resistance, blocking voltage increases significantly. Additionally, reducing sidewall electric field could reduce sidewall leakage current and improve blocking voltage, so using inductive coupled plasma reactive ion etching equipment etched different sidewall structure. Also, ion implantation is used for isolation process to avoid side wall leakage current and better blocking voltage is expected. The thickness 20um with 5um concentration 1×1015 cm-3 and 15um concentration 1×1016 cm-3 epitaxy structure with integration of all technology has the lowest specific on-resistance of 0.61 mΩ-cm2, and the breakdown voltage is over 2870 V. The corresponding Baliga’s Figure of Merit (BFOM) is over 13.5GW/cm2.

Chapter 1 introduction 1
1-1 Background of Gallium nitride (GaN) 1
1-2 Power diodes 2
1-3 Gallium nitride on free-standing Gallium nitride substrate 4
1-4 Research Motivation 6
Chapter 2 Fundamental Principles 8
2-1 Structure of p-i-n diode 8
2-2 Forward conduction characteristic 9
2-2-1 Recombination current 10
2-2-2 Low-level injection current 12
2-2-3 Conductivity modulation at high-level injection 14
2-3 Characteristic of p-i-n under reverse bias 15
2-4 Edge termination 18
2-4-1 Bevel edge terminations 19
2-5 Baliga’s figure of merit 22
Chapter 3 Experimental Procedure 23
3-1 Fabrication processes of free-standing GaN p-i-n diodes 23
3-2 Experiment details of free-standing GaN p-i-n diodes 27
3-3 Measurement systems 37
Chapter 4 Result and Discussion 38
4-1 Different etching profile under SEM 38
4-2 Secondary ion mass spectrometry analysis of p-i-n structure 39
4-3 Calculation of contact resistance by Transfer Length Method 42
4-4 Capacitance-voltage characteristics of the GaN p-i-n diodes 47
4-5 Characteristic of different etching profile power diode 51
4-5-1 Simulation results of different etching profile power diode 56
4-6 Effects of p-GaN activation, p-contact metal and epitaxy structure 59
4-6-1 Device characteristic of structure A 60
4-6-2 Device characteristic of structure B 65
4-7 Effects of different isolation method by using ion implantation 70
4-8 Variable temperature measurement of p-i-n diode 75
4-8-1 Forward bias pulse mode measurement 76
4-8-2 Forward bias DC mode measurement 80
4-8-3 Reverse bias DC mode measurement 83
Chapter 5 Conclusion 87
References 89

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