Beweglichkeitsanisotropie und Relaxation warmer Elektronen inn-Typ Germanium

The nonohmic part of the electric conductivity ofn-type germanium in a weak electric field depends on the field direction in the crystal. Measurements were made both with d.c. and microwave fields at lattice temperatures between 85 and 273° K. The anisotropy decreases with increasing field frequency and temperature. The data show that the effect of the effective mass anisotropy is enhanced by intervalley scattering. From the measured frequency dependence of the conductivity anisotropy the intervalley relaxation time is calculated and compared with results obtained from the acoustoelectric effect. In 〈001〉-direction where all 〈111〉-valleys of the conduction band are equally populated, the conductivity between 200 and 273° K is in accordance with theoretical results obtained byAdawi for an isotropic model; at lower temperature there are deviations even if ionized impurity scattering is included in the theory. The energy relaxation time is calculated from the measured frequency dependence of the 〈001〉-conductivity and compared with previous results.