Measurement of the Electron Velocity-Field Characteristics in Germanium Using a New Technique

A new method is described that combines the Shockley---Haynes experiment with the time-of-flight technique. This technique allows absolute measurement of the velocity-field characteristic in materials too impure to be measured by the latter method. Measurements have been made with this technique on Ge, InSb, and Si, but only the Ge measurements will be reported here. It is demonstrated that negative differential mobility (NDM) occurs in the electron velocity characteristic for the {100} direction, at a temperature as high as 200 ^∘{}K. At 77 ^∘{}K, the NDM is as large as 275 cm²/V sec. By applying uniaxial pressure, it is possible to enhance the NDM. A value of 1000 cm²/V sec is obtained at 110 ^∘{}K, for a pressure of 9 kbar, with electron motion in the [112̄] direction, and pressure applied along the [111] direction.