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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim ~2000~\Omega $ </tex-math></inline-formula>/sq and linear ohmic contact resistance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.54~\Omega \cdot $ </tex-math></inline-formula> mm. A HFET with a gate length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim ~200$ </tex-math></inline-formula> nm, source-drain spacing of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4~\mu $ </tex-math></inline-formula>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<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text {T}}\text {)}$ </tex-math></inline-formula> 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<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> V. This JFOM value is one of the highest reported JFOM values for AlxGa<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text {1-{x}}}$ </tex-math></inline-formula>N channel HFET (x >0.4) and also for other ultra-wide bandgap (UWBG) transistors.