Investigations of the static characteristics, responsivity, internal noises, and detectivity of the forward biased p-i-n
photodetectors made on wide bandgap compensated semiconductors operating in double injection regime are presented.
Noise related calculations are performed by utilizing "Impedance Field Method". Numerical simulations are made
assessing 4H-SiC and GaN biased p-i-n photodiodes noise related characteristics. It is shown that forward biased p-i-n
photodiodes have low level of thermal and generation-recombination noises and high values of sensitivity and detectivity
at the room temperature.
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".
Process of the origin and relaxation of the fluctuation of distribution function of conduction electrons in space-homogenous and non-degenerate equilibrium semiconductors is discussed. The fluctuations of electron distribution function, formed as result of the internal fluctuations of the phonon system, are studied. The physical mechanisms of the origin and following slow (diffusion) damping of the equilibrium fluctuations of the electron and phonon distribution functions are represented. It is shown that in low frequency region the Fourier-component of distribution function fluctuations of predominantly long wavelength electrons and phonons are depends on frequency by law ω<sup>-1/2</sup>.
The influence of surface scatterings on damping of the equilibrium fluctuations of the electron distribution function, originating in the bulk of homogeneous, bounded semiconductors is discussed as a result of random phonon-phonon scatterings. The peculiarities of (acoustic) phonons refraction on the flat interface are investigated. It is shown that only certain discrete magnitudes of phonons wave vectors satisfy the refraction laws. So-called "refraction points" are discovered. It is established that relaxation of longer-wavelength electron distribution function fluctuation depends on processes of surface reflection and refraction of electrons and phonons. It is shown that in the semiconductors with not very large sizes the damping is also conditioned by the phonons quasi-momentum direction diffusion. It the microscopic mechanism of such diffusion is analyzed.
The two main causes of origin of the mobility fluctuation of the electrons in homogeneous, unlimited, and non-degenerated semiconductors are discussed. It is shown that the mobility fluctuation is conditioned by the symmetric component of the fluctuation of the distribution function, i.e. by the fluctuations of the conduction electrons energy. On the base of the developed quasi-classical model the spectrum of electrons lattice mobility fluctuations is calculated. In the frequency wide variation range it has 1/<i>f</i> form.
The current internal fluctuations appearing in the homogeneous, unlimited and non-degenerate semiconductors having parabolic band structure are investigated. At the considered case the external electric field is absent and the semiconductor is in thermal equilibrium state. For the definiteness only the behavior of the conduction electron system is considered. It is shown that equilibrium fluctuations of the electron current, conditioned by the fluctuations of the electron quasi-momentum, are describing by fluctuations of the asymmetric component of the electron distribution function. The following mechanism of these fluctuations is suggested. During the random phonon-phonon scattering the fluctuations of the quasi-momentum of acoustic phonons are coming into existence, which are transmitting to the electron system via electron-phonon interactions. On the base of this mechanism, the spectral density of the electron current equilibrium fluctuations <i>S<sub>I</sub></i>(ω) is calculated. It is shown that <i>S<sub>I</sub></i> ≈ <i>const</i> in the frequency range ω < ω<sub>0</sub>. In the frequency range ω><sub>0</sub> < ω < ω<sub>1</sub>, frequency dependence of spectrum <i>S<sub>I</sub></i>(ω) described by 1/ω law, and in the range ω > ω<sub>1</sub> it is described by 1/ω<sup>2</sup> law. The characteristic frequencies ω<sub>1</sub> and ω<sub>0</sub> are determined by parameters of semiconductors being under investigation as well as by processes of scattering and diffusion of electrons and phonons in quasi-momentum space.