Research On The Characteristics Of4H-SiC MESFET With A L-Gate And A Partial P-Type Spacer

Owing to the superior properties and the relatively mature device fabricationtechnology, SiC MESFET is considered to be one of the most promising devices for thenext-generation high power, high frequency, high efciency, compact radio frequencyand microwave(RFandMW) electric circuit applications even under an extremely badenvironment. Although SiC MESFETs have good DC and RF power performances intheory,their superiority for high frequency and high power applicationsis still did notexerted fully.However, because of a potential trade-off between the further increment ofdrain current and breakdown voltage(Vb) the enhancement of power density is verylimited. Similarly there is a trade-off between the RF and power performance.Therefore, inorder to overcome this imbalance between power and small-signalcharacteristics, as well as further simultaneous improvement in DC, RF and powercharacteristics. For the first time, we propose a4H-SiC MESFET with the combinationof L-gate and partial p-type spacer (LP-MESFET). The L-gate can reduce the depletionlayer under the gate and decrease the gate capacitance. Because of a wider conductchannel released under the L-gate, the saturation drain current can be increasedeffectively. The L-gate structure has lower and upper gates, which effectively controls athinner and a thicker part of the channel, respectively. Since the partial p-type spacermodulated the channel transversal electric field, the distribution of the depletion layerunder the gate was changed. As a result we obtained a smaller gate-drain capacitancecompared with the conventional4H-SiC MESFET. This paper also studied theoptimization of the thickness and the doping concentration of the partial p-type spacer.The simulations show that obvious improvements can be obtained for the LP-MESFETcompared to the conventional structure(C-MESFET), such as a17%larger of thesaturation current and a36%higher of the breakdown voltage Vb. The maximumtheoretical output power density Pmaxfor the4H-SiC C-MESFET and LP-MESFET is4.2W/mm and8.2W/mm, respectively. It means that the proposed LP-MESFETstructure has about95%larger output power than that of the C-MESFET structure.