Analysis of the substantial reduction of strain-induced mobility enhancement in (110)-oriented ultrathin double-gate MOSFETs

The stress effect in uniaxially strained (100)- and (110)-oriented double-gate silicon-on-insulator nMOSFETs is analyzed. A model of the siliconthickness- dependent deformation potential (D_ac-T_Si) is used to accurately calculate the mobility by considering the quantum confinement effect. The mobility enhancements in the (100) and (110) orientations were found to exhibit considerably different silicon thickness dependencies. As the silicon thickness decreases, the mobility enhancement in the (100) case exhibits a second peak, whereas it diminishes in the (110) case. This phenomenon results from differences in the quantization mass that affect the energy differences between the first subbands of two- and four-fold degenerate valleys.