Hole mobility enhancement of Si by rhombohedral strain

The strain technology is an effective way to improve hole mobility and CMOS device performance. Tetragonal strain leading to hole mobility enhancement in strained Si (001) has been verified by two aspects of theories and experiments. In this paper, we aim to study rhombohedral strain effect on the hole mobility of Si, which results from growing on the (111) oriented relaxed Si1-x Ge (x) substrate. It is found that structure transformation of Si from cubic to trigonal system occurs under the biaxial tensile stress imposed by the (111) substrate and that its corresponding averaged hole mobility increases about one time at most in comparison with one of unstrained Si. The results can provide valuable reference to the understanding of the strained Si material physics and its design.