Origin of the shear piezoresistance coefficientπ44ofn-type silicon

It is shown that the origin of the shear piezoresistance (PR) coefficient ${\mathrm{\pi }}_{44}$ of n-type silicon is a stress-induced effective-mass change of individual valleys rather than the stress-induced intervalley electron transfer, which has long been believed to be the dominant source of PR in many-valley semiconductors. An orthorhombic stress destroys the rotational symmetry of the ellipsoidal valleys and induces large effective-mass changes due to the special character of the conduction-band edge of silicon. The effective-mass anisotropy then leads to a transverse voltage when the current is along [100]. This mechanism predicts a sign and a magnitude of ${\mathrm{\pi }}_{44}$ for n-type Si that are consistent with experiments hitherto known.