Design And Simulation Of Double Recessed 4H-SiC MESFETs With Different Source Field Plate

silicon carbide(Si C) based Metal Semiconductor Field Effect Transistor(MESFET) has been widely investigated during the last few years. Owing to the superior material properties and the advantage of the structure as well as the relatively mature device fabrication technology, Si C MESFET is very competitive for the microwave power applications, and has been considered to be an excellent device operating under harsh environment such as high temperature, high voltage and high radiation. Although Si C MESFET has good DC and RF performances, to further improve the performance is limited by the power--frequency trade off. The breakdown voltage and the drain current are difficult to increase simultaneously, while the promotion of the power density usually leads to a deterioration of the frequency response.In order to overcome the power--frequency trade off, improve the DC and RF performance comprehensively, for the first time, a double recessed gate 4H-Si C MESFET with stepped source field plate is proposed. The double recessed gate is constituted by an upper gate and a lower gate, the upper gate makes a thinner channel which ensures a large drain saturation current, while the lower gate allows the gate to control the channel efficiently. Meanwhile, the effective length of the double recessed gate is short, the transit-time is reduced and the frequency response is improved. By set a field plate electrically connected the source electrode, a depletion layer is formed under the field plate. The depletion layer extends the distribution region of the equipotential line at the channel surface, and modulates the channel electric field making the spread of the electric field more uniform, the breakdown voltage is enhanced. The depletion reduce the gate drain capacitance significantly as well. The scales of the stepped source field plate are optimized to meet an optimal result. The evidence finally obtained indicates that the proposed structure enhances the breakdown voltage from 50 V of the double recessed gate 4H-Si C MESFET to 199 V which means more than 298% increment with almost the same saturation drain current. The maximum output power density of the stepped source field plate structure is 9.25W/mm, which means nearly 4 times more than the double recessed gate 4H-Si C MESFET. Themaximum available gain is significant improved as well.