Comprehensive Understanding of Coulomb Scattering Mobility in Biaxially Strained-Si pMOSFETs

In this brief, the effect of biaxial tensile strain on the hole mobility limited by substrate-impurity and interface-state Coulomb scatterings (mu_sub and mu_it, respectively) in an inversion layer of (100)/lang110 rang pMOSFETs is investigated experimentally with strained-Si (s-Si) channels on relaxed Si_1- xGex (x = 0.1-0.4) substrates. Our results show that biaxial tensile strain degrades the hole mobility limited by substrate-impurity Coulomb scattering (mu_sub) , while it enhances the hole mobility limited by interface-state Coulomb scattering (mu_it) because of the increase in the average distance between holes and scattering centers at the Si/SiO₂ interface after the tensile strain. These trends are opposite to that of electron ones. The different strain dependence between electrons and holes in terms of mu_sub and mu_it can be explained by a universal two-band model based on the subband structures of electrons and holes.