(Invited) Gate Stack Technology for Advanced AlGaN/GaN Mos-Hemt Power Devices

Abstract

AlGaN/GaN high electron mobility transistor (HEMT) has gained much attention as next-generation high frequency and high power devices. Since AlGaN/GaN HEMT with Schottky gate is restricted in device application due to large gate leakage current and normally-on operation, metal-oxide-semiconductor (MOS) gate stack with deposited gate insulator has been widely investigated to overcome these limitations. Among various insulating materials, aluminum based oxide such as Al2O3 is one of the potential candidate because of its wide bandgap and high thermal stability. However, large amount of interface traps at MOS interfaces severely degrade both carrier mobility and threshold voltage (Vth) stability. Furthermore, significant electron injection into Al2O3 layer causing positive Vth shift was often observed for Al2O3/AlGaN/GaN MOS-HEMT. We have recently reported that N incorporation into Al2O3 (aluminum oxynitride) significantly reduces not only the negative fixed charges but also the electron traps in Si and SiC MOS devices. In this study, superior physical and electrical properties of AlON gate dielectrics on AlGaN/GaN substrates were demonstrated. We fabricated high-quality AlON/AlGaN/GaN MOS capacitors with improved stability against charge injection and a reduced interface state density. Moreover, the impact of nitrogen incorporation into the gate insulator will be discussed on the basis of results from physical characterizations.