Optimization of GaN MOS capacitors and FETs

Abstract

AbstractIn this paper, three different gate oxide processes were explored and compared. All MOS capacitors were fabricated on n‐type GaN epitaxial layers grown by MOCVD on sapphire substrates. C‐V measurements were performed on the three samples and their characteristics were compared. The very small interface‐state density makes OX3 a very good process choice for GaN MOSFETs and the trend of decreasing interface‐state density deeper into the bandgap allows the demonstration of GaN inversion‐mode MOSFET.Both accumulation and inversion‐mode MOSFETs were fabricated and characterized using OX3 process conditions. Field‐effect mobilities were extracted on both circular and linear devices with different channel lengths. Mobilities in two perpendicular directions in (0001)‐plane show similar values. Current collapse testing was also performed on our GaN MOSFETs and no current collapse was observed. In addition, an NMOS inverter stage, utilizing an enhancement‐mode MOSFET and a depletion‐mode MOSFET has also been demonstrated and characterized. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)