The origin of electron mobility enhancement in strained MOSFETs

Straining Si MOS structures has been known to enhance electron mobilities. However, the origin of the effect has remained elusive as conventional modeling can only account for it by large ad hoc reduction of macroscopic interface roughness. Here, we report first-principle fully quantum-mechanical mobility calculations based on an atomic-scale interface model. Wave-function penetration into an oxide is automatically included. The results demonstrate that atomic-scale departures from abruptness (Si-Si bond on the oxide side, and Si-O-Si on the Si side) naturally lead to enhanced mobilities in strained structures in quantitative agreement with available data. The results have important ramifications for mobility models in nanoscale devices.