INTERVALLEY TRANSFER AND MICROWAVE CURRENT OSCILLATIONS IN STRAINED n-TYPE GERMANIUM

Microwave current oscillations have been observed in uniaxially compressed n-type germanium in high electric field. For the configuration where the current is along the [112̄] crystal axis, and the strain along the [111] direction, the effect is present at 27°, 77°, and 300°K. At 27°K, the oscillations begin at stress of 1500 kg/cm2; the threshold electric field has a minimum of 270 V/cm at a stress of 5000 kg/cm2. These values are higher at higher temperatures. The phenomenon is believed to be due to the existence of a region of bulk negative differential conductivity which results from intervalley transfer of electrons between the stress-split 〈111〉 valleys of the conduction band.