Theory of electron-mobility degradation caused by roughness with long correlation length in strained-silicon devices

To study the influence of surface roughness of a strained-Si/SiGe heterostructure on electron mobility, electron-transport properties were investigated with the ensemble Monte Carlo method. This investigation assumed an electron-motion-deviation model, in which the direction of momentum of electrons is deflected according to the roughness in the channel. It was found that (i) degradation of electron mobility appears even if the correlation length of the roughness is larger than 100 nm and (ii) significant degradation of drift velocity occurs when the direction of momentum of electrons is changed by increasing roughness amplitude. It is, therefore, concluded that decreasing the amplitude of the roughness with long correlation length is the appropriate way to increase electron mobility.