Scattering mechanisms in silicon carbide MOSFETs with gate oxides fabricated using sodium enhanced oxidation technique

The improvement of the SiC-SiO₂ interface has been the main focus of research in SiC MOSFET technology due to the presence of high density of interface traps (D_it) leading to poor threshold voltage temperature stability and poor mobility. In SiC MOSFETs with the gate oxide grown in the presence of sodium, known as sodium enhanced oxidation(SEO), a lower D_it and higher field effect mobility has been observed[1]. Hall effect measurements were performed from 125°K-225°K on such MOSFET samples. The Hall measurements were made as a function of temperature for various sheet charge concentrations. The sheet charge density was measured as a function of gate bias at 225°K and there is very little trapped charge in the sample with oxide grown by SEO while about 50 % of the total charge is trapped in a sample with N₂O grown oxide annealed in NO. In samples with oxide grown by SEO, there is a monotonic increase in mobility with sheet charge density and the mobility also increases with temperature. This is an indication that the main scattering mechanism is Coulomb scattering in this regime.