64% AlGaN Channel HFET With High Johnson’s Figure of Merit (>6 THz·V)

In this letter, we report a heterostructure field effect transistor (HFET) with Al0.87Ga0.13N barrier and Al0.64Ga0.36N channel grown by metalorganic chemical vapor deposition (MOCVD). TLM measurements of the structure showed a sheet resistance of $\sim ~2000~\Omega $ /sq and linear ohmic contact resistance of $4.54~\Omega \cdot $ mm. A HFET with a gate length of $\sim ~200$ nm, source-drain spacing of $4~\mu $ m showed a peak transconductance of ~40 mS/mm and a high peak drain current of ~0.6 A/mm. A current gain cutoff frequency (f $_{\text {T}}\text {)}$ of 15.7 GHz and a power gain cutoff frequency of 20.4 GHz was observed. The breakdown voltage of this device is 390 V, yielding a high Johnson’s figure of merit (JFOM) of 6.1 THz $\cdot $ V. This JFOM value is one of the highest reported JFOM values for AlxGa $_{\text {1-{x}}}$ N channel HFET (x >0.4) and also for other ultra-wide bandgap (UWBG) transistors.