Surface-Dependent1fNoise in Germanium

Abstract

The surface characteristics of $\frac{1}{f}$ noise have been investigated by using field effect techniques on 100 micron thick single crystal germanium filaments. The $\frac{1}{f}$ noise is independent of the surface potential when an accumulation layer is on the surface but increases rapidly as the surface conductivity gradually becomes inverted with respect to the bulk. No $\frac{1}{f}$ noise is observed due to charge transfer between the bulk and the slow surface states. An increase in the $\frac{1}{f}$ noise associated with the inversion layer occurs when the temperature of the germanium is decreased. The magnitude of the $\frac{1}{f}$ noise depends on the ambient, increasing as the slow state relaxation time decreases. An investigation of the relaxation processes associated with the charge transfer between the bulk and the slow surface states after the application of a dc electric field to the field effect electrode reveals a $\frac{1}{f}$ noise relaxation which is independent of the mode of the conductivity relaxation. The noise relaxes back to its original value with a logarithmic time dependence which is characteristic of a $\frac{1}{\ensuremath{\tau}}$ distribution in time constants and the conductance decays with a combination of exponential and logarithmic terms, depending on the surface conditions.