Theoretical Investigation Of Silicon Carbide Materials And Silicon Carbide Based MOS Devices

ii Silicon carbide shows the advantage in the application of device electronics which include high temperature, high power and radio resistance devices. In addition, silicon carbide is the only one among the compound semiconductors having the native oxide of silicon dioxide. Thus, silicon carbide based metal-oxide-semiconductor field effect transistor (MOSFET) has draw considerable attention and excited great interest. This dissertation aimed at the study of the material characteristics of silicon carbide and silicon carbide based MOS devices.In p-type silicon carbide, the excited states of dopants play an important role, but they are given a little attention. In this dissertation, the effect of excited states on ionization of dopants, inversion-layer charge density of n-channel MOSFET and MOS capacitor is investigated. The influence of excited states relates to temperature, the doping concentration and the depth of energy level of dopants. Under the effect of excited states, the inversion-layer charge density of n-channel MOSFET is lowered,and the impact of excited states are important under the threshold voltage. Under the influence of excited states, the kink effect of the C-V characteristic curve of the MOS capacitor round the flatband is weakened, and the curve produces a small horizontal displacement.There has remarkable valley-orbit splitting in n-type silicon carbide. However, the established distribution function for electrons did not include it. In this dissertation, a new distribution function for electrons is obtained by introducing the average increment and average partition function of all split levels. The influence of the valley-orbit splitting on ionization of dopants, inversion-layer charge density of p-channel MOSFET and MOS capacitor is investigated.Under the effect of the valley-orbit splitting, the inversion-layer charge density of p-channel MOSFET is lowered and the kink effect of the C-V characteristic curve of the MOS capacitor round the flatband is weakened.In order to utilize the advantage of silicon carbide for IC designer, the sufficient and accurate compact model of MOSFET has to be set up. During establishing the compact model, the temperature-dependent channel-electron mobility model is very important. In this dissertation, it is established by considering the existed and new factors. In addition, a new method extracting interface state parameters and fixed oxide charge density by simulating with the experimental temperature-threshold voltage curves is introduced.An explicit expression of surface potential is essential to the surface-potential-based MOSFET compact model. In the existed expression which suits silicon based MOSFET, interface trapped charge was not included, and dopants were considered to be ionized completely. However, it was not true for silicon carbide based MOSFET. High density interface states lie at SiC/SiO2, and freeze-out effect exists in silicon carbide. In this dissertation, we obtain the explicit expression of surface potential suitable to silicon carbide based MOSFET under the consideration of the two factors mentioned above.On the whole, this dissertation investigated four aspects around material characteristics of silicon carbide and silicon carbide based MOS devices. The most important part is about MOS devices.