Study On The Large-signal Model And Microwave Power Combination Of 4H-SiC MESFET

Silicon Carbide (SiC) is a promising material in the applications of power microwave, high temperature, optoelectronics, and radiation resistant due to its excellent properties such as wide band gap, high electron saturated velocity, high breakdown electric field, high power density, high thermal conductivity, etc. With these excellent figure of merits of SiC, the great attention was paid on 4H-SiC MESFET (metal semiconductor field effect transistor) .Modeling of 4H-SiC MESFET is of great importance in design of microwave/RF(Radio-Frequency) devices and circuits, wherein characterization of large-signal is complicated and crucial. Up to the present, there is not mature approach for physically-based large-signal model of SiC MESFET. Therefore it is necessary to develop a model of SiC MESFET which is clear in device mechanism description and simple in calculation for the design and optimization of device and circuits.In this work, one of the emphases is put on the nonlinear modeling of SiC MESFET, wherein the Drain current Ids and the Gate capacitance C_gs, C_gd are the key parts of the large-signal equivalent circuit. With the properties of the incomplete impurity ionization and the higher saturated electron drift velocity, a quasi-analytical model of drain current characteristics for 4H-SiC RF power MESFET is proposed. A large-signal nonlinear capacitance model for RF power 4H-SiC MESFET is also proposed by combining the physical analysis of devices based on theories of charge controlling with the description of empirical models such as Statz and Angelov models. Based on the nonlinear modeling of 4H-SiC MESFET presented in this thesis, a 4H-SiC MESFET RF power combination circuit is designed with the software ADS(Advanced Design System).