Experimental Determination of Shear Stress induced Electron Mobility Enhancements in Si and Biaxially Strained-Si Metal–Oxide–Semiconductor Field-Effect Transistors

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Electron mobility enhancements under uniaxial, biaxial and shear stress have been experimentally discriminated by applying mechanical stress to Si and biaxially strained Si/SiGe(001) n-channel metal–oxide–semiconductor field-effect transistors (MOSFETs). Additive stress effects on mobility enhancements among uniaxial, biaxial and shear stress for different biaxial strain levels are deduced and the physical mechanisms of these various stress-induced mobility enhancements are highlighted. It is found experimentally that the shear stress impact on mobility in Si is fully additive to the biaxial tensile stress electron mobility enhancement. The shear stress, with its band warping mechanism, is thus effective to boost the electron mobility and to overcome the saturation of the biaxial stress mobility enhancement with its valley population mechanism. The warping of the 2-fold valleys and the effective mass change induced by the shear stress component included in $\langle 110\rangle$ uniaxial stress is experimentally quantified in this study. The $0.19m_{0}$ transverse effective mass $m_{\text{t}}$ of 2-fold valleys valleys is found to be reduced by 10% for 400 MPa shear stress.
2010-07-25