Elimination of the Low Resistivity of Si Substrates in GaN HEMTs by Introducing a SiC Intermediate and a Thick Nitride Layer

We report the effect of a thick nitride layer on the high-frequency performance of AlGaN/GaN high-electron-mobility transistors (HEMTs) grown by metal oxide chemical vapor deposition (MOCVD) on a 6-inch Czochralski (Cz)-Si substrate. The thick nitride layer was grown via a 3C-SiC intermediate layer. A significantly low parasitic pad capacitance and a comparable cutoff frequency of 4.5 GHz for 2- $\mu \text{m}$ gate length devices were achieved along with excellent electron transport characteristics, such as a mobility of ~2200 cm ² /V-s and a drain current density of 520 mA/mm. The extracted small-signal equivalent circuit parameters also verified the accuracy of the measured cutoff frequency and parasitic capacitances.