Papers by Author: J.R. Williams

Abstract: Large group-I elements such as sodium, rubidium and cesium have recently been incorporated in the gate oxide of SiC power MOSFETs. In the case of sodium incorporation, enhanced field effect mobilities have been definitively observed. Based on density functional calculations, we find large group-I elements serve as a shallow impurities near the interface. The enhanced mobility, observed in the case of sodium, can be explained in terms of an impurity band model.

Abstract: The electrical properties of the SiO₂/SiC interface fabricated by sodium-enhanced oxidation (SEO) of n-type 4H-SiC were studied by temperature-dependent C-V and constant-capacitance deep level transient spectroscopy (CCDLTS). With the exception of near-interface traps in the SiC epi-layer, which are not present in the SEO samples, the trap species observed in SEO capacitors are the same as those observed in both standard-oxidized and NO-annealed MOS capacitors. Total electron trapping in accumulation is comparable in SEO and NO-annealed capacitors; however, the traps in SEO capacitors are located at the interface whereas tunneling into oxide traps is observed in NO-annealed samples. A series of bias-temperature stress tests show that electron trapping is essentially unchanged when mobile sodium ions are moved toward the interface. The improved mobility attained by this process compared to NO annealing may be due to the absence of near-interface SiC traps in SEO samples.