節約能源是目前全世界各主要工業國家積極推動的政策，方法之一就是提高電子產品的效率。電源交換與供應器是電力、電子模組與系統不可或缺的組件，相關電子元件與電路的節能特性扮演關鍵角色。此研究之主題為電力電子電路中常用的蕭基二極體之設計與製作。傳統的功率蕭基二極體是以矽材料為主，若以氮化鎵材料取代之，可具有低導通電壓、高崩潰電壓、低漏電流以及快速切換特性等優點，對於電源切換模組效率之提高、體積尺寸之減小，都有很大潛力。 蕭基二極體順偏操作狀態下，主要的功率損耗來源為導通電壓以及導通電阻。當蕭基二極體由順偏切換至逆偏狀態時，主要的功率損耗來自於切換期間內之電荷耗損。而在截止狀態時的功率損耗則主要來自於蕭基二極體的漏電流。為了降低蕭基二極體在各方面的耗損，本研究以AlGaN/GaN異質結構為基礎，採用陽極蝕刻方式降低蕭基能障，導通電壓可從1.3 V下降至0.6 V；另一方面，為了改善蕭基二極體的逆向偏壓特性，本研究採用了氟離子處理方式，使用SF6電漿將氟離子植入於陽極未蝕刻區域，有效使漏電流由12 μA下降至4 μA，崩潰電壓由400 V提升至455 V。此外，氟離子能夠減少陽極蝕刻過後在側壁所產生額外的寄生電容，使蕭基二極體在逆向偏壓為20 V的情況下，總空間電荷能夠由152 pC下降之125 pC，並使逆向回復時間下降至約10 ns，逆向回復電荷下降至約5 nC。本研究亦將元件置於高溫(150 oC)、高電壓(-200 V)壓力測試25小時，結果顯示，相較於平面製程元件，以陽極蝕刻及氟離子摻雜製程所製作之元件有較緩之劣化情形，表示元件中的氟離子還算相當穩定。 ;High power AlGaN/GaN Schottky barrier diodes (SBDs) are essential switching devices for high efficiency power supplies and modules. The requirements on these SBDs include low turn-on voltage (Von), low on-resistance, high breakdown voltage (VB), low reverse leakage current (IR), and high switching speed. However, lowering Von by reducing Schottky barrier height has to be compromised with the increase in reverse leakage current. Although it has been shown that anode recess to the positions near or over the two-dimensional electron gas (2DEG) of AlGaN/GaN heterostructures can reduce turn-on voltage (Von) from ~1.5 V to ~0.4 V, this process might cause high IR due to the defects generated by the etching processes. In this work, we propose a novel way, i.e. anode recess and SF6 plasma treatment, to cope with this problem so that AlGaN/GaN SBDs can have a low turn-on voltage as well as a high reverse breakdown voltage simultaneously. Turn-on voltage (Von) can be reduced from 1.3 V to 0.6 V, reverse breakdown voltage (VB) can be increased from 400 V to 455 V at the expense of slight increase of on-resistance, meanwhile reverse recovery time can also be reduced from 12.9~14.4 ns to 9.6~10.7 ns. Moreover, less degradation is observed on the devices fabricated by the anode recess and fluorine ions implantation processes after stressing the devices at 150 oC, -200 V for 25 hours, indicating the stability of this new method.
