Valley-Orbit Splitting of Antimony in Germanium

Abstract

The change of electrical conductivity under uniaxial tension and compression has been measured over the range 4°K to 7°K for single-crystal specimens of germanium doped with antimony. The stress was varied from 1×${10}^7$ to 5×${10}^8$ dynes/${\mathrm{cm}}^2$. On the basis of Price's calculation of the effect of shear on the Kohn-Luttinger donor level structure, an expression for the piezoresistance has been derived, which includes terms of high order in the strain. It is shown that for a finite valley-orbit splitting, i.e., a finite energy separation between the onefold and the threefold $1s$-like donor states, shear increases the total electron concentration in the conduction band. For uniaxial stresses along the [110] direction this increase in electron concentration is an even function of stress and can, therefore, be determined from a linear combination of the piezoresistance measured under tension and compression. A comparison of the theoretical expression with the experimentally obtained change in electron concentration yields for antimony in germanium a valley-orbit splitting of 0.57±0.03 milli-electron volt.