First-Principles Simulation on Thickness Dependence of Piezoresistance Effect in Silicon Nanosheets

We have simulated the piezoresistance coefficients of single-crystal silicon nanosheets on the basis of the first-principles calculations of model structures. The carrier conductivities of the hydrogen-terminated silicon nanosheet models with (001) surface orientation have been calculated using band carrier densities and their corresponding effective mass tensors derived from the two-dimensional band diagram by our original approach for a small amount of carrier occupation. The p-type shear piezoresistance coefficient for principal axes on the (001) plane increases in connection with the longitudinal and transverse ones for the [110] tensile stress, as the thickness of the nanosheet decreases. We have obtained a high piezoresistance coefficient pi(s) of 450 x 10(-11) Pa-1 for an approximately 1 nm thick silicon (001) nanosheet model. It is expected that the p-type ultrathin silicon (001) nanosheet will be a suitable candidate for nanoscale piezoresistors owing to its giant piezoresistivity. (C) 2010 The Japan Society of Applied Physics