Recent progress and material issues of high power and high frequency AlGaN/GaN HFETs

Performances of AlGaN/GaN HFETs have much improved recently and very high potential of this heterostructure for high power and high frequency electronic devices has been verified. Application of new device technologies such as field plate, recessed gate, digital pre-distortion circuit and dual field plate was essential to realize such high device performances both at 2 GHz, 5GHz and 26 GHz. However, practical requirements on the quality and structure of these material systems for production of these devices are still not clear. Extensive studies on correlation between material quality and device performances were carried out under Japanese NEDO project. This paper reviews recent progress of the performances of high power and high frequency AlGaN/GaN HFETs. Then, several interesting results which suggest practical requirements on material quality and structure will be discussed based on our extensive characterization studies in terms of device performances and reliabilities.