250W S-band 4H-SiC MESFET

Internally-matched 4H-SiC MESFET with 4times20 mm of the total gate width was demonstrated. The SiC MESFET structure consists of a channel layer with doping concentration of 2.3times10¹⁷ cm^-3 and a cap layer with doping concentration of 1.5times10¹⁹ cm^-3. A lightly p-doped buffer layer was employed between the substrate and the channel layer. Dry etching and high-temperature oxidation were employed to expose the channel layer and remove the surface damage for the gate. The ohmic contact resistivity of 2times10^-6 Omegaldrcm² was achieved. The pulsed (300 mus, 10%) output power, gain and power-added efficiency of the internally-matched device measured at 2 GHz were 250 W, 10.5 dB, and 30%, respectively.