Effect of Gaseous Ambients upon 1/ f Noise in Germanium Filaments

The variation of 1/f noise in thin, single crystal germanium filaments was investigated by using gaseous ambients to change the surface potential of the sample. The noise samples, having a thickness of only 4 μ, were extremely sensitive to variations in the surface potential and exhibited large fractional changes of the total sample conductance as a result of the surface conductance fluctuations which were interpreted as the 1/f noise. These experimental results showed a definite noise minimum when the sample surface potential corresponded to the sample conductance minimum. The rms conductance fluctuation varied roughly linearly with ΔG, where ΔG is the increase of the sample conductance with respect to the minimum value. The slope of the curve for the condition of an accumulation layer on the sample surface was an order of magnitude less than that for the inversion layer. The amplitude of the accumulation noise agreed (within a factor of two) with the prediction of McWhorter's majority carrier trapping effect, but the inversion noise was an order of magnitude greater.