On the Quasi-Saturation in State-of-the-Art Power MOSFETs

The quasi-saturation (QS) effect in a power MOSFET has been discovered several decades ago. As the field has evolved and the dimensions in power MOSFETs have changed from tens of micrometers to submicrometer levels, and the gate geometry has evolved from planar to trench, the origin and the effect of the QS need to be re-assessed. This letter first discusses the origin of the QS effect in the state-of-the-art power MOSFETs and subsequently analyses the phenomenon of majority carrier injection (or diffusion) and its contribution to the increased carrier concentration in the drift region, specific to quasi-saturation.