氮化鋁銦/氮化傢之綠能應用功率元件開發

Abstract

因環保意識的抬頭，近年來，對於綠色能源科技及節能應用上，高功率電子元件扮演著相當關鍵性的角色。在此需求之下，由於氮化鎵(GaN)具備低導通電阻和高崩潰電壓的材料特性，利用氮化鎵所製造而成的高電子遷移率電晶體(HEMT)近年來已經成為高功率電子元件的不二人選。傳統的GaN HEMT 結構是由AlGaN和GaN組合而成，由於AlGaN和GaN之間存在著晶格常數的差異及材料本身原子排列的不對稱性，而在界面處引發了自發性(Spontaneous)及壓電(Piezoelectric)極性，使得在界面處形成了高密度(~1*1013 cm-2)的二維電子氣層(2DEG)。在高功率元件應用方面，一般來說，為了提升元件的功率，所採取的方式是增加在AlGaN中Al含量，以提高二維電子層中的載子密度，然而一但Al的含量超過30%，存在於AlGaN中的應力卻會開始讓AlGaN晶體品質往下降，甚至表面會出現裂痕，這個缺點成為了AlGaN/GaN HEMT發展上的限制。為了解決此限制，利用AlInN取代AlGaN當能障層即可有效的解決應力的問題，理由是因為當銦的含量被控制在~17%時，AlInN的晶格常數是和氮化鎵一致的，因此可獲得無應力(strain-free)狀態的AlInN。此外即便在界面處無壓電極性的產生，AlInN材料亦能提供比AlGaN還要大的自發性極性。因此在二維電子氣層中提供了更高濃度的載子(>2*1013 cm-2)。所以在材料和元件參數最佳化下，利用AlInN/GaN所製造出來的高功率元件，其功能較傳統的AlGaN/GaN為佳是可被期待的。本計劃預計將利用金屬有機化學氣相沉積(MOCVD)方式，把AlInN/GaN材料成長於矽基板上以更符合經濟效應，並製作輸出功率大於1kW的單顆元件，以驗證此材料符合未來功率元件的應用開發。

High efficiency power device is one of the key factors for green energy applications and sustainable management. In this regard, the GaN high electron mobility transistor (HEMT) with a low turn-on-resistance and high breakdown voltage is the most potential candidate for future power electronics. The advantages of a conventional GaN HEMT, consists of an AlGaN/GaN structure, for power handling attribute to the wide bandgap material property and high carrier concentration (~1x103 cm-2) in the 2-diamensional electron gas (2DEG) channel resulting. However, the inherent strain in the AlGaN barrier layer imposes limitations on the device performance and reliability. The degradation or cracking of AlGaN barrier layer, which may occur for Al content larger than 30%, will limit the generation for higher carrier concentration in the 2DEG channel. Therefore, the development of AlInN as barrier layer offers a potential solution to the strain problem since it can be grown lattice-matched to GaN with In~17%. Furthermore, the strain-free AlInN barrier with larger spontaneous polarization also induces much higher carrier density (>2x1013 cm-2) in the 2DEG channel. Therefore, higher power density can be expected from the AlInN/GaN HEMT if other material and device parameters are optimized. In this study, the AlInN/GaN material will be grown on Si substrate by using metal-organic chemical vapor deposition (MOCVD) system. GaN HEMT on Si substrate is important for the development of high efficiency and cost effective devices. With the optimized growth conditions and device fabrication techniques, we hope to demonstrate an AlInN/GaN HEMT device with output power larger than 1kW.