The main mechanisms of the conduction electrons mobility fluctuations, originating in n-type semiconductors with
electron traps are investigated. It is shown that the current carriers mobility fluctuations are determined by the energy
fluctuations. Fundamental sources of electron mobility fluctuations are established. The first source is established to be
related with a non-elasticity of electron random scattering processes: intraband scatterings and electronic transitions
"trap-conduction band". The second source of mobility fluctuations is established to be related with random character of
the transitions of conductance electrons trough the potential barriers of p-n junctions or/and ohmic contacts.
The influence of the surface and interfaces of semiconductor-metal Al/n<sup>+</sup>Si-nSi/Al and Ag/n<sup>+</sup>Si-nSi/Ag structures with different aluminum and silver contact coating layers on the level and behavior of the low frequency current noise spectra was experimentally investigated. It is shown that the level of low frequency noise strongly depends on the material and form of the contact coating layers. At the room temperature, at the frequency 10 Hz, the noise level for Al/n<sup>+</sup>Si-nSi/Al structures is equal to ~ 10<sup>-15</sup> A<sup>2</sup>/Hz, for the Ag/n<sup>+</sup>Si-nSi/Ag structures is equal to ~ 10<sup>-17</sup>-10<sup>-18</sup> A<sup>2</sup>/Hz. It seems possible that the interface conditions modification, which in its turn mirrors at the processes of surface reflection and refraction of electrons and phonons, affects on the relaxation processes of longer-wavelength electron distribution function fluctuation and thus on mobility fluctuation and 1/f noise level as well. On the base of noise spectral characteristics of the mentioned structures the peculiarities of the acoustic phonons refraction on the semiconductor-metal flat interface are experimentally investigated. Several practical aspects related with so-called "refraction points" are discussed. It is proposed that, by manipulation of those phonons "refraction points" at hetero-interface, it will be possible to suppress the part of 1/f noise level, which arises in the volume of semiconductor. It is supposed that the hetero-interface by itself is not the source ("generator") of the 1/f noise, but probably is a factor of the volume 1/f -noise "reduction".
The influence of the built-in electric field (e.g. several potential barriers, impurity gradients, etc) at presence of external crossed electric and magnetic fields on the level of low-frequency noise is theoretically studied by the use of interrelated Langevin type Boltzmann transport equations for the systems of electrons and phonons for non-degenerate n-type semiconductors. At the first time it is shown that within the context of the proposed problem the built-in field causes origin of separate 1/f-noise component, which, besides the main parameters of semiconductor, depends also on the value of this field. The spectral density of this component by the form is similar to the Hooge's empirical formula. For the parameter analogous to the Hooge parameter <b>α</b> the comparison with experimental data for n-type Si is carried out. It is shown that for range of values of the built-in electric field from 50 to 600 V/m at low temperatures from 77K to 150K, the longitudinal component of the analog of the Hooge parameter varies from 10<sup>-6</sup> up to 10<sup>-4</sup>, which in some cases may exceed corresponding values of the generally observed 1/f-noise. The transversal component of the Hooge parameter analog has square dependence on external magnetic field intensity; even for low temperature region, at values of magnetic field from 50 to 400 A/m it has very low values and varies from 10<sup>-15</sup> up to 10<sup>-11</sup>. Basing on the calculations a physical model describing the origin of built-in component of 1/f-noise is proposed. It explains the mechanism of origin of the additional component and helps to shed light on the origin of the general 1/f-noise.