| SiC is a very promising candidate for high temperature, high power, high frequency, relatively low noise and radiation hardness applications. In this research, the temperature dependent DC, small-signal AC and noise performances of 4H-SiC MESFET are studied by using two dimensional numerical Drift-Diffusion model.; Combining numerical technique, materials physics, and measured device characteristics, the DC simulator is used to extract more information about the physical parameters of 4H-SiC, including the mobility, velocity-field curve and the Schottky barrier height. Temperature dependent I-V characteristics and breakdown behaviors are studied with the inclusion of temperature dependent intrinsic band gap narrowing, incomplete shallow impurity ionization, low field mobilities, saturation velocities; and impact ionization rate. As the temperature increases, the DC I-V characteristics degrade which is mainly due to mobility reduction. Due to the negative temperature dependence of impact ionization rate, the breakdown voltage of 4H-SiC MESFET increases as temperature increases.; A set of general boundary conditions for non ideal metal-semiconductor contact has been introduced that takes into account a thin interfacial layer and interface energy states. It has been demonstrated that the 10 dB/dec small-signal current gain roll-off can be attributed to the existence of high density interface states at the metal-semiconductor interface. As the gate length is reduced to 0.1 μm, fT and fmax can reach as high as 30 GHz and 62 GHz, respectively. Although the high temperature small-signal performance of the 4H-SiC MESFET degrades due to mobility reduction, the high frequency response is still very attractive for high temperature RF applications.; Device noise spectra are studied by solving Langevin equation through Green's function approach. Under thermal equilibrium condition, a perfect match between the simulation and fluctuation-dissipation theorem has been found. As the applied voltage increases, the deviation between the simulation and fluctuation-dissipation theorem enlarges. Qualitative agreement between the simulation and the experimental result about the minimum noise figure has been reached, while the simulation result is always smaller than the experimental value. As the device operating temperature increases, the minimum noise figure degrades gradually. |
