"Current Striction"—A Mechanism of Electrostriction in Many-Valley Semiconductors

Previously reported experiments tentatively suggest that electric fields applied to germanium produce deformations which are about ${10}^4$ times as large as those expected from conventional electrostriction mechanisms. We have calculated the magnitude, temperature dependence, and angular dependence of this effect for $n$-type many-valley semiconductors. Our model does not involve a polarization in real space but, like the current, is mediated by a shift of the electron distribution in reciprocal space. This field-induced shift increases the energy of the electrons within each valley, but the increase is largest in those valleys with smallest effective mass parallel to the field direction. It then becomes energetically favorable for the lattice to deform in such a way that the deformation potential lowers the energy of the high-curvature valleys at the expense of the low-curvature valleys. We calculate a much larger effect in germanium than in silicon, predicting also that the induced strain should be a pure shear in germanium, and a pure volume-preserving linear dilatation in silicon.