Enhancement-Mode N-Polar GaN MOS-HFET With 5-nm GaN Channel, 510-mS/mm $g_{m}$, and 0.66-$\Omega\cdot \hbox{mm}$$R_{\rm on}$

We report enhanced dc and small-signal RF performance of enhancement-mode (E-mode) metal-oxide-semiconductor heterojunction field-effect transistors (MOS-HFETs) in N-polar GaN technology with an ultrathin 5-nm GaN channel and graded AlGaN back-barrier structure with a record on-resistance (R on) of 0.66 Ω mm. The device has a maximum drain current (I d) of 1.15 A/mm, a peak transconductance (g m) of 510 mS/mm, and a peak current-gain cutoff frequency (f t) of 122 GHz, with a positive threshold voltage (V th) of 1.6 V. The device shows improved saturation and pinchoff characteristics compared to the previously reported N-polar E-mode HFETs with a maximum I onrm off ratio of 2.2 × 10 5. © 2011 IEEE.