Piezoresistance in Heavily Dopedn-Type Germanium

Piezoresistance has been measured as a function of temperature in $n$-type germanium specimens with donor concentrations between 6×${10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$ and 3×${10}^{19}$ ${\mathrm{cm}}^{-3\mathrm{}}$. The results obtained can be explained on the basis of the accepted multivalley model, provided that statistical degeneracy is taken into account. An analysis of the degeneracy observed in the data provides strong evidence for the four-ellipsoid model of the conduction band. The data are consistent with the assumption that there is no appreciable dependence of the effective mass, deformation potential constant, and mobility anisotropy factor on the Fermi level or impurity density. No piezoresistance effect due to the (100) valleys is detected, showing that these valleys are at least 0.11 ev above the minima of the (111) valleys.