Simulation and Optimization of SiC Field Effect Transistors

Silicon Carbide (SiC) is a wide band-gap semiconductor material with excellent material properties for high frequency, high power and high temperature electronics. In this work different SiC field-effect transistors have been studied using theoretical methods, with the focus on both the devices and the methods used. The rapid miniaturization of commercial devices demands better physical models than the drift-diffusion and hydrodynamic models most commonly used at present. The Monte Carlo method is the most accurate physical methods available and has been used in this work to study the performance in short-channel SiC field-effect devices. The drawback of the Monte-Carlo method is the computational power required and it is thus not well suited for device design where the layout requires to be optimized for best device performance. One approach to reduce the simulation time in the Monte Carlo method is to use a time-domain drift-diffusion model in contact and bulk regions of the device. In this work, a time-domain drift-diffusion model is implemented and verified against commercial tools and would be suitable for inclusion in the Monte-Carlo device simulator framework. Device optimization is traditionally performed by hand, changing device parameters until sufficient performance is achieved. This is very time consuming work without any guarantee of achieving an optimal layout. In this work a tool is developed, which automatically changes device layout until optimal device performance is achieved. Device optimization requires hundreds of device simulations and thus it is essential that computationally efficient methods are used. One important physical process for RF power devices is self heating. Self heating can be fairly accurately modelled in two dimensions but this will greatly reduce the computational speed. For realistic influence self heating must be studied in three dimensions and a method is developed using a combination of 2D electrical and 3D thermal simulations. The accuracy is much improved by using the proposed method in comparison to a 2D coupled electro/thermal simulation and at the same time offers greater efficiency. Linearity is another very important issue for RF power devices for telecommunication applications. A method to predict the linearity is implemented using nonlinear circuit simulation of the active device and neighbouring passive elements. The work has contributed to a substantial improvement in the area of device simulation and increased efficiency in device design in general, but particularly for SiC RF power MESFETs.