An improved structure of silicon carbide metal-semiconductor field-effect transistors (MESFET) is proposed for high power microwave applications.Numerical models for the physical and electrical mechanisms of the device are presented,and the static and dynamic electrical performances are analysed.By comparison with the conventional structure,the proposed structure exhibits a superior frequency response while possessing better DC characteristics.A p-type spacer layer,inserted between the oxide and the channel,is shown to suppress the surface trap effect and improve the distribution of the electric field at the gate edge.Meanwhile,a lightly doped n-type buffer layer under the gate reduces depletion in the channel,resulting in an increase in the output current and a reduction in the gate-capacitance.The structural parameter dependences of the device performance are discussed,and an optimized design is obtained.The results show that the maximum saturation current density of 325 mA/mm is yielded,compared with 182 mA/mm for conventional MESFETs under the condition that the breakdown voltage of the proposed MESFET is larger than that of the conventional MESFET,leading to an increase of 79% in the output power density.In addition,improvements of 27% cut-off frequency and 28% maximum oscillation frequency are achieved compared with a conventional MESFET,respectively.
