Measurements of Noise Spectra of a Point Contact Germanium Rectifier

Measurements have been made of the excess noise produced by a point-contact germanium rectifier in the frequency range 0.117 c/s to 14 Mc/s at 29.5°C, with the reverse direct current I as parameter. The experimental noise spectral density is shown to consist of three well-defined types of component: ( a ) a basic component ∝ f -1 detectable over as many as seven decades of frequency, ( b ) two components ∝ [1 + (2π f τ) 2 ] -1 associated with single relaxation times τ=τ 1 and τ 2 , ( c ) a uniform component detectable at high frequencies. There is no simple dependence of these densities on current, except that the uniform component is equal to shot noise for small currents. τ 1 and τ 2 are found to be dependent on I .