A quasi-two-dimensional depth-dependent mobility model suitable for device simulation for Coulombic scattering due to interface trapped charges

摘要

The silicon carbide (SiC)-silicon dioxide (SiO_2) interface in SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) has shown the presence of a very large number of trap states. These traps become filled during inversion causing a lowering of conduction charge in the inversion layer, and increases Coulombic scattering of mobile charges. Owing to the large number of occupied interface traps, Coulomb interaction is likely to be an important scattering mechanism for SiC MOSFET device operation, resulting in very low surface mobilities. We have developed a first principles physics-based Coulomb scattering mobility model to understand this phenomenon and to study its effect on mobility in SiC devices. This type of Coulombic scattering is a quasi-two-dimensional phenomenon. Mobile charges located closer to the interface are scattered at a higher rate than those located far away from the interface. Screening of the traps and fixed oxide charges by the inversion layer mobile charges causes a decrease in the scattering rate. Also, at higher temperatures, due to a reduction in occupied trap density, and increasing energy of mobile charges, Coulombic scattering is greatly reduced. Our mobility model incorporates and accounts for all these effects. We have implemented this physics-based Coulomb scattering mobility model into a device simulator and have obtained agreement with experimental current-voltage characteristics.