Germanium Fet--A Novel Low-Noise Active Device

A novel device for low-noise amplification-the germanium junction field-effect transistor (JFET)--is introduced. The properties of germanium and silicon at cryogenic temperatures are summarized. Based on the conclusions of this summary, a theoretical comparison between germanium and silicon JFET´s is made, followed by a comparison of commercially available JFET´s from both materials. A low-noise preamplifier featuring liquid-helium-cooled germanium JFET´s was built and operated with semiconductor radiation detectors. Pulse generator resolution of the preamplifier for zero external capacitance is 0.28 keV FWHM (Ge) with a slope of 0.018 keV/pF. Actual resolution obtained with the silicon detector for low-energy x rays is 0.37 keV.