| Due to the change in lattice constant and the distortion of energy band, strained Si exhibits great mobility enhancement compared with the conventional Si material, and it is the critical reason for the wide application of strained Si MOSFETs. In order to design strained-Si MOSFETs more efficiently, it is necessary to thoroughly analysis the mechanism behind mobility enhancement and thus establish related model to clarify the relationship between mobility and strain.In this paper, the subband structure in the inversion layer is constructed by solving the self-consistent Schr?dinger equation, thus the carrier effective mass and scattering rate can be obtained. Furthermore, taking account for the carrier density in each subband, we establish carrier mobility model in strained-Si MOSFET. Calculation results show that 90% carriers will populate in the first ten subbands when effective field is larger than 105V/cm. Influence of strain on subband structure is described by a factor Dk, which is the phonon induced band deformation potential extracted from experiment data. In strained Si conduction band, the value of Dk is 2.4 times larger than its Si counterpart.For strained Si PMOSFETs, the hole mobility is not only determined by the tensity of strain, but also related to the strain types, which are uniaxial compressive strain and biaxial tensile strain. When electric field is high enough, the hole mobility will be deteriorated in PMOSFETs under biaxial tensile strain, however, in the case of uniaxial compressive strain, the deterioration will never occur.Both the theoretical simulation and experiment results show that the relationship betweenμeff and Eeff in strained-Si is similar to the one in bulk Si. The mobility reaches its maximum when Eeff equals to 2×105V/cm. In strained-Si PMOSFET with Si0.76Ge0.24 substrate, the mobility enhancement factor is 1.25. However, as the Ge content in SiGe substrate surpasses 40%, the mobility enhancement in strained Si PMOSFET becomes saturated. |
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