High‐Current‐Density Enhancement‐Mode Ultrawide‐Bandgap AlGaN Channel Metal–Insulator–Semiconductor Heterojunction Field‐Effect Transistors with a Threshold Voltage of 5 V

Enhancement‐mode ultrawide‐bandgap Al 0.65 Ga 0.35 N/Al 0.4 Ga 0.6 N metal–insulator–semiconductor heterojunction field‐effect transistors are demonstrated using fluorine‐plasma treatment for threshold voltage control and Al 2 O 3 as gate dielectric. The device exhibits a threshold voltage of 5 V, a maximum drain current density of 105 mA mm −1 , and a transconductance of 19 mS mm −1 . In addition, the capability to achieve low off‐state current density at 3–4 × 10 −9  mA mm −1 , an exceptionally low gate leakage current density of 1.4 × 10 −8  mA mm −1 even at a high forward gate bias of V GS  = 12 V, and a current on/off ratio >10 10 is shown. Small signal measurement shows that the device has a unity current gain cutoff frequency f T of 3.8 GHz and power gain cutoff frequency f max of 4.5 GHz.