Low-temperature mobility due to unscreened charged impurities in compensated semiconductors

It is proved that within the Fujita theory, the low-temperature values of mobility of charged carriers in compensated semiconductors due to scattering on charged unscreened impurities result temperature independent. The value of is determined by material parameters including the correlations in space among impurities but it is completely independent of the concentration of the charged impurities.     

Low-temperature mobility due to unscreened charged impurities in compensated semiconductors

For the problem of electron scattering on charged unscreened impurities, the scattering rate is calculated self-consistently. The resulting low-temperature mobility is only, slightly temperature dependent and differs from an analogous result of Fujita et al. (J. Phys. Chem. Sol.37 (1976), 227) and Zubarev et al. (Sol. State Commun.21 (1977), 565) by just a change of a numerical constant.     

Effect of photoheating of electrons on the properties of compensated semiconductors

It is shown that even a small contribution to the total density of the high-energy tail in the electron distribution during impurity photoexcitation can change noticeably such properties of a compensated semiconductor as its Hall mobility and, in particular, the capture coefficient at repulsing Coulomb centers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 13–16, February, 1984.The author is grateful to V. L. Bonch-Bruevich for discussion.     

Scattering of electrons by charged dislocations in InSb-type semiconductors

Electron scattering by parallel arrays of charged dislocations in InSb-type semiconductors is considered. In the theoretical approach the nonparabolic structure of the conduction band of the semiconductors considered is taken into account in the approximation of a simplified Kane's band model. The effect of screening by free electrons of the dislocation charge is also included in the theory. The calculated relaxation time of the electrons is used to derive a formula for the dislocation-limited electron mobility in the semiconductors. Some examples of calculations of the charged dislocation-limited mobility as a function of the electron concentration with the dislocation density as a parameter are given for n-InSb at 77 K and 300 K. The ratio of the magnitudes of the charged dislocation-limited mobility to the ionized impurity-limited mobility in n-type material at low temperatures is also discussed.     

Elastic and inelastic scattering of electrons by vibrating impurities in semiconductors

Elastic and inelastic scattering of conduction electrons by vibrating ionized impurities in valence semiconductors is investigated. For elastic scattering, the modification of the Brooks-Herring formula arising from impurity vibrations is unimportant for all conceivable electron temperatures and donor concentrations. Similarily, for inelastic (one-phonon) processes, the change in electron-phonon relaxation time (or in electron-lattice coupling constant) arising from vibrations of the ionized centres is entirely negligible.     

Fluctuation model of the high-frequency hopping electrical conductivity of moderately compensated semiconductors with hydrogenic impurities

A model is developed according to which a hop of an electron (or hole) between two hydrogenic donors (or acceptors) occurs only when their energy levels become equal due to thermal and/or electrostatic fluctuations in a doped crystal. The main contribution to the real part of the high-frequency hopping electrical conductivity is assumed to come from acceptor pairs in which the time of hole tunneling is equal to the half-period of the external electric field and the phase of tunneling coincides with that of the field. In this case, the imaginary and real parts of the hopping conductivity are approximately equal. The results of calculations based on this model are compared to the experimental data for p-Ge: Ga with an intermediate degree of compensation of the main doping impurity.     

Hot electrons in semiconductors

Journal of Russian Laser Research -     

Scattering of conduction electrons by impurities in quantizing magnetic fields and calculation of electrical conductivity

The method of partial phases was used to obtain a formula for the electrical conductivity of conduction electrons scattered by impurities in quantizing magnetic fields for the case of an anisotropic carrier spectrum, when its isoenergetic surface is an ellipsoid of revolution, and the magnetic field is parallel to its major semiaxis. Equations for finding the phase shifts are given.Translated from Izvestiya Vysshikh Uchebynkh Zavedenii, Fizika, No. 2 pp. 98–102, February, 1978.In conclusion we thank Prof. A. Samoilovich and Docent S. L. Korolyuk for help in conducting this work.     

Scattering in graphene with impurities: A low energy effective theory

We analyze the scattering sector of the Hamiltonians for both gapless and gapped graphene in the presence of a charge impurity using the 2D Dirac equation, which is applicable in the long wavelength limit. We show that for certain range of the system parameters, the combined effect of the short range interactions due to the charge impurity can be modelled using a single real parameter appearing in the boundary conditions. The phase shifts and the scattering matrix depend explicitly on this parameter. We argue that this parameter for graphene can be fixed empirically, through measurements of observables that depend on the scattering data.     

Far-infrared spectroscopy of impurities in semiconductors

Far-infrared spectroscopy of the electronic transitions between bound states of impurities provides a very high resolution technique for studying chemical shifts and thereby identifying residual contaminants. The use of photoconductivity generated within the sample itself, usually by the photothermal mechanism (“photothermal ionisation spectroscopy”), enables very high sensitivity to be achieved even with very thin films or ultrahigh-purity material. The current knowledge about the identity of the residual shallow donors in GaAs, InP, InAs and InSb obtained with this technique is reviewed. With high-purity materials the magneto-optical spectrum of the shallow donors can be particularly rich and more than fifty lines can be observed with both GaAs and InP.

Hydrostatic pressure provides a valuable additional experimental parameter in studies of impurities. Not only does the pressure-induced increase in mass improve the resolution of the “fine structure” due to different chemical species but additional states can be introduced into the forbidden energy gap. Results with both InSb and GaAs have shown that generally donors in direct-gap III-V materials may be expected to have three types of state: the familiar gamma-associated donors, localised states with A₁ symmetry which are normally resonant within the conduction band and metastable DX states.

Negatively charged shallow donor states (D^- states) and “molecular” combinations where the electrons are shared between two or more donor sites have been studied by infrared spectroscopy of III-V materials. These states are important precursors of the metal-insulator transition.

Recently there have been a number of studies of impurities within quantum wells and heterostructures. The dependence of impurity energy on distance from the well edge has been established and it has been shown that high concentrations of D^- states can be formed by remote deping of the structures.     

Shallow donor impurities in magnetic semiconductors

We introduce the macroscopic magnetization to treat the localized magnetic moments in a magnetic semiconductor. We obtain a set of coupled equations for the magnetization and the electronic wavefunction of a shallow donor impurity exchange coupled to the localized moments. A variational solution to the equations of motion indicates that near to the critical temperature the wavefunction contracts and the electron becomes more bound. We discuss the relevance of this model for the understanding of the activation energy for conductivity in the paramagnetic phase of EuO.     

Non-equilibrium dynamics for impurities in semiconductors

This paper summarizes the ‘first-principles’ calculations of the vibrational properties of impurities, which are critical to the optical identification of defects. The issue of temperature control for non-equilibrium molecular dynamics (NEMD) is discussed. Applications of NEMD include the calculations of the temperature-dependence of vibrational lifetimes and of the thermal conductivity of semiconductors as a function of their impurity content.     

High-frequency hopping conductivity and permittivity in compensated semiconductors

In semiconductors, high-frequency conductivity is caused by polarization reversal of the collective states of a pair of impurity atoms under the action of the random electric fields of all the impurities. A Coulomb correlation which appreciably increases the conductivity is established as a result of the statistical distribution of the particles over four levels of the diatomic system. The relaxation absorption and the permittivity of the entire pair system are calculated allowing for these statistics.     

Electron mobility in compensated semiconductors at low temperatures

Electron mobility in compensated semiconductors for ionised impurity scattering is calculated. A simple screened dipole potential is used. The calculations differ from those of Stratton due to the fact that in this paper the mobility is exactly calculated.     

Scattering theory and ground-state energy of Dirac fermions in graphene with two Coulomb impurities

We study the physics of Dirac fermions in a gapped graphene monolayer containing two Coulomb impurities. For the case of equal impurity charges, we discuss the ground-state energy using the linear combination of atomic orbitals (LCAO) approach. For opposite charges of the Coulomb centers, an electric dipole potential results at large distances. We provide a nonperturbative analysis of the corresponding low-energy scattering problem.