An in-depth simulation study of Coulomb mobility in ultra-thin-body SOI MOSFETs

A comprehensive study of Coulomb-limited mobility in ultra-thin-body SOI MOSFETs is presented. Mobility curves for structures with interfacial charges at the gate oxide–semiconductor interface, at the buried oxide–semiconductor interface and simultaneously at both interfaces are calculated by means of Monte Carlo simulations. Coulomb-limited mobility is then isolated applying Matthiessen's rule. It is shown that the Coulomb-limited mobility due to the charges placed simultaneously at both interfaces is just the superposition of the effects separately produced by the charges at each interface. We also show that the influence of the silicon layer thickness on Coulomb-limited mobility strongly depends on the interface where the charges are located; the influence of the charges at the buried oxide–semiconductor interface rapidly weakens as the silicon layer is made thicker, while if the charges are placed at the gate oxide–semiconductor interface, Coulomb-limited mobility is scarcely modified with the silicon layer thickness.