Band offset induced threshold variation in strained-Si nMOSFETs

Due to the offset in the valence band, strained-Si nMOSFETs exhibit a -100 mV threshold shift and 4% degradation of the subthreshold slope per each 10% increase of Ge content in the relaxed SiGe layer. The correlation between the threshold shift and strained layer thickness is investigated based on device simulations. In a certain range of the strained-Si layer thickness, the threshold and subthreshold slope change gradually, posing a concern of larger device parameter variation. A larger threshold distribution is observed in devices fabricated with a strained layer thickness comparable to the depletion depth.