Numerical Study of the Piezoresistance Effect inp-Type Si

Piezoresistance (PR) of p -type Si, consistent with experimental ones, has been obtained by numerically calculating the conductivity for the degenerate valence bands with and without stress. Small stress coefficients for total bands and even each band well fulfil the symmetry relationship for the PR coefficient in the cubic crystal. It is found that the mobility of each hole linearly changes with stress, while the carrier concentration change is of the second order in stress. This leads to a conclusion that the principal mechanism of PR in p -type Si is the stress proportional mobility change of holes, the carrier redistribution effect which is the mechanism for many valley semiconductors being ruled out. Experimental temperature dependence of a PR coefficient which exhibits (1/ T )-like and saturation behaviors is also explained in terms of that of mobility change of holes. It has been suggested that deviation of energy dependent hole conductivity masses from bulk hole masses may be responsible for hole mobility change.