Importance of inter-valley phonon scattering on mobility enhancement in strained Si MOSFETs

It has recently been reported that strained Si MOSFETs fabricated with relaxed SiGe layer exhibit very high mobility at room temperature, almost twice as high as that in conventional Si MOSFETs. While strained Si MOSFETs, compatible with Si LSI technology, are promising as the devices for the high speed, room temperature applications, the understanding of the carrier transport in strained Si is still lacking. In order to clarify the mechanism of the mobility enhancement, calculations of the subband structure and phonon-limited mobility in the inversion layer of strained Si were performed for the first time, compared with the calculations for the inversion layer of unstrained (conventional) Si. The effect of the band splitting due to strain was successfully incorporated in the subband calculation. It is demonstrated that the suppression of inter-valley phonon scattering is essential to the mobility enhancement in strained Si MOSFETs.