1 f hopping noise in crystalline germanium

The low-frequency current noise (f = 0.1-50 Hz) has been measured in samples of p-Ge〈Ga〉 and n-Ge〈As〉 at temperatures 1.3-4.2 K, where the d.c. conductivity is determined by the nearest-neighbour-hopping mechanism of charge transport. It is shown that the spectral density of the noise has a 1 f-form and is proportional to the square of the applied voltage in accordance with the Hooge formula. However, the temperature dependence of the noise is much weaker than that of the d.c. resistivity, which is controlled by the concentration of mobile carriers in the critical network. Possible explanations of this effect are discussed.