Energy Spectrum Of Charge Carriers Research Articles

Influence of the Lateral Electrostatic Field on the Statistical Distribution of Charge Carriers in a Cylindrical Nanolayer of β-HgS

Analytical expressions are obtained for the wave functions and the energy spectrum of charge carriers in the β-HgS nanolayer of a cylindrical core/shell/shell β-CdS/ β-HgS/ β-CdS nanocomposite in the presence of a strong lateral uniform electrostatic field. It is shown that, under the influence of an external field, the position of the chemical potential of the electron-hole subsystem at absolute zero shifts to the bottom of the conduction band of the sample. The displacement value is determined by the intensity of the external field and increases linearly with increasing field. The concentration, internal energy, and heat capacity of the electronic subsystem of the β-HgS layer in the presence of a field are compared with similar values in the absence of a field. Calculations show that under identical conditions, the presence of an external field leads to an increase in the carrier concentration, which in turn leads to an increase in the internal energy and heat capacity of the system of electrons and holes in the layer.

Influence of Boundary Conditions on Quantum Magnetotransport in a Thin Film

Analytical expressions are obtained for the Hall coefficients and the magnetoresistance of a thin semiconductor film. The case of a weak magnetic field is considered and the effects related to the splitting of the energy spectrum of charge carriers into Landau levels are not taken into account. The isoenergetic surface of a semiconductor material is an ellipsoid of revolution (spheroid). The transition to the limiting cases of degenerate and nondegenerate electron gases and mirror boundaries is carried out. The behavior of charge carriers is described by the quantum Liouville equation. The effect of the surface scattering of charge carriers is taken into account through the Soffer boundary conditions. The dependence of the Hall coefficients and magnetoresistance on the film thickness, induction of an external magnetic field, and film surface roughness is analyzed.

Scanning photodielectric spectroscopy of CdZnTe crystals under additional non-monochromatic illumination

By means of the Scanning Photodielectric Spectroscopy (SPDS) method, the energy spectrum of charge carriers’ localized states was acquired for Cd1-xZnxTe crystals (x = 0.08–0.15) grown from the melt. In the implementation of SPDS, an additional excitation of a crystal by non-monochromatic light was used for the first time, and the parameter ‘spectral density of a section of the photodielectric effect diagram’ was introduced. This parameter is closely related to the occupation of localized states of charge carriers. It is found that under additional photoexcitation, the energy spectrum of the localized states detectable by the SPDS method broadens. Determinate variations in the new parameter depending on the energy position of a localized state in the crystal bandgap were found and explained.

Preface

The 9th International Conference on Materials Science (ICMS2020) was held at the National University of Mongolia from September 10 to 13, 2020 in Ulaanbaatar. Unfortunately, the global pandemic had a bad effect on the event. Therefore, some of the participants could not attend the conference in person. A significant part of the participants (more than 50 people) were accommodated in the hall and more than 25 people participated in absentia. Since at this time it is difficult to predict the end of the pandemic, and the termination of the exchange and discussion of scientific results may negatively affect the research of many scientific groups, it was decided to hold this traditional conference using video presentations. Participants from Russia presented their reports and presentations in electronic form (video reports and posters) and were demonstrated at section meetings. In total - about 80 participants.Organisers were some known scientific organizations:National University of Mongolia, Ulaanbaatar, Mongolia, National University of Mongolia, Mongolia, Inner Mongolian Normal University, China, Institute of Physical Materials Science, Siberian Branch of the Russian Academy of Sciences, Russia, Mongolian Academy of Sciences, Mongolia, German-Mongolian Institute for Resources and Technology and Erdenet Mining Corporation SOE, Mongolia.Scientific committee was consisted of famous scientists:Prof. J.Davaasambuu (National University of Mongolia)Prof. U.Pietsch (University of Siegen, Germany)Prof. G.Eckold (University of Goettingen, Germany)Prof. O.Tegus (Inner Mongolian Normal University, China)Dr. A.Nomoev (IPMS SB RUS, Russia)Prof. S.Gorfman (Tel Aviv University, Israel)Prof. S.Bardakhanov (Buryat State University, Russia)Prof. P.Daniel (Le-Mans University, France)Prof. B.Battsengel (GMIT, Mongolia)Dr. B.B.Damdinov (SFU, Krasnoyarsk, Russia)Acad. O.Penyazkov (A.V.Lykov Institute, Belarus)Acad. D.Sangaa (Mongolian Academy of Sciences)Acad. J.Temuujin (Mongolian Academy of Sciences)Dr. V.Koledov (IRE, RAS, Russia)Dr. P.Altantsog (Mongolian Academy of SciencesAll materials were reviewed by the editors: Dr. N. Tuvjargal and Prof. J.Davaasambuu from Department of Physics, Faculty of Arts and Sciences, National University of Mongolia.The conference consisted of plenary presentations for 30 minutes and session reports for 15 minutes. There were 35 oral reports and 29 posters in total. The organizers have provided 5 minutes for questions that can be asked in person or via the Internet.The objectives of the conference were to bring together scientists working in the field of materials science from around the world, to exchange ideas, recent research results in this area and to offer a platform for the initiation of scientific cooperation between Mongolian and foreign scientists. The conference was focused on the structures, properties and applications of new materials as well as their characterization techniques.Topics were: Materials science, Condensed matter physics, Computational methods, Experimental methods and instrumentation, Laser spectroscopy.At the conference, nanotechnology-related studies related to quantum effects, such as carrier tunneling, controlled changes in the structure of energy bands, quantization of energy spectra of charge carriers and spin phenomena, and the study of new physical features of semiconductor nanostructures, were discussed. The topic were a description of the transport properties of various ion-exchange membranes, crystallization of supercooled liquids and amorphous solids, increase the corrosion resistance of aluminum alloys, obtaining nanoscale metal and alloy powders. Numerical simulation of phonon crystals with time-dependent properties of a periodic structure, computer simulation by the molecular dynamics method, the processes of structure formation of nanoclusters of an alloy of silver and copper were presented.The organizers and participants of ICMS 2020 noted the high scientific level of the presented reports.

Electron-Hole Liquid in Monolayer Transition Metal Dichalcogenide Heterostructures

Monolayer films of transition metal dichalcogenides (in particular, MoS2, MoSe2, WS2, and WSe2) can be considered as ideal systems for the studies of high-temperature electron-hole liquids. The quasi-two-dimensional nature of electrons and holes ensures their stronger interaction as compared to that in bulk semiconductors. The screening of the Coulomb interaction in monolayer heterostructures is significantly reduced, since it is determined by the permittivities of the environment (e.g., vacuum and substrate), which are much lower than those characteristic of the films of transition metal dichalcogenides. The multivalley structure of the energy spectrum of charge carriers in transition metal dichalcogenides significantly reduces the kinetic energy, resulting in the increase in the equilibrium density and binding energy of the electron-hole liquid. The binding energy of the electron-hole liquid and its equilibrium density are determined. It is shown that the two-dimensional Coulomb potential should be used in the calculations for the electron-hole liquid.

Effect of Carbon on the Thermoelectrical Properties of Copper Oxide-Based Composites

The effect of carbon filler on the electrical resistance, thermopower and thermoelectric power factor of copper oxide-based composites has been studied. It is established, that thermoelectrical properties of investigated composites are determinated by interaction between filler and matrix materials at phase boundaries. This interraction leads to changes in the energy spectrum of charge carriers. It is found that in composites CuO – CNF (carbon nanofibers) the dependences of the electrical resistivity and the thermopower on the filler concentration are characteristic by s - like curves that are typical for percolation systems. While using fullerene as filler material the dependences of the electrical resistivity and the thermopower on the filler concentration cannot be explain within percolation theory

Energy Levels of Quantum Ring in ABA-Stacked Trilayer Graphene

We present the solutions of the energy spectrum of charge carriers confined in a quantum ring in ABA-stacked trilayer graphene subjected to a perpendicular magnetic field. The calculations were performed in the context of the continuum model by solving the Dirac equation for a zero width ring geometry, i.e., freezing out the carrier radial motion. We show that the obtained energy spectrum exhibits different symmetries with respect to the magnetic field and other parameters. Moreover, the applied potential shifts the energy spectrum vertically while the applied magnetic field breaks all symmetries. We compare our results with those of the ideal quantum ring in monolayer and bilayer graphenes.

Intraband Radiation Absorption by Free Holes in GaAs/InGaAs Quantum Wells with Allowance for Nonsphericity of the kP Hamiltonian

A system of Kane’s equations has been derived and solved with allowance for elastic stresses and nonsphericity of the kP Hamiltonian. On this basis, analytic expressions for the energy spectra of charge carriers have been obtained and calculations of the optical absorption coefficient for heavy holes with transition to a spin-orbit-split hole band in GaAs/InGaAs quantum wells (QWs) have been performed for various polarization directions of the incident radiation. It is established that the maximum absorption in GaAs/InGaAs heterostructure takes place at a QW width of 4–6 nm.

Внутризонное поглощение излучения свободными дырками в квантовых ямах GaAs/InGaAs с учетом несферичности kP-гамильтониана

The system of Kane equations is derived and solved with taking into account the elastic stresses and the nonsphericity of the kP Hamiltonian. Analytical expressions for the energy spectra of charge carriers are obtained. The radiation absorption coefficient by heavy holes with transition to the spin-split zone in GaAs/InGaAs quantum wells was calculated for different directions of polarization of the incident radiation. It was shown that for the GaAs/InGaAs heterostructure, the maximum absorption will be observed when the QW width is 4–6 nm.

Shubnikov–de Haas Oscillations in the Magnetoresistance of Layered Conductors in Proximity to the Topological Lifshitz Transition

The dependence of the resistance of a layered conductor with a quasi-two-dimensional charge carrier energy spectrum on the strength and orientation of a quantizing magnetic field is studied. The case of an organic conductor with a multisheet Fermi surface consisting of a weakly warped cylinder and two adjoining planar sheets is considered. By applying an external pressure to the conductor or doping it with impurity atoms, the gap between the cylinder and the planar sheets of the Fermi surface (FS) may be reduced so that electrons start wandering on the FS, tunneling between its different parts due to magnetic breakdown. If an electron can pass through all the different sheets of the FS several times during the mean free time, its motion in the plane orthogonal to the magnetic field becomes finite. This leads to Shubnikov–de Haas oscillations with a period determined by the area enclosed by the closed breakdown orbit of an electron in momentum space. However, even at a slight tilting of the field from the normal to the layers by an angle ϑ, the equidistance is broken and at certain angles ϑk the probability of the magnetic breakdown to one of the planar FS sheets may become so low that the electron cannot complete the magnetic-breakdown orbit and its motion over the other planar sheet and the cylindrical part of the FS becomes infinite. As a result, magnetic-breakdown quantum oscillations of magnetization and all kinetic properties vanish. This vanishing repeats periodically as a function of tan ϑ with changing the tilt angle. Possibilities for experimental observation and investigation of the influence of magnetic breakdown on quantum oscillation phenomena are discussed.

Inhomogeneous metal oxide films with a fractal structure as an object for observation of quantum size effects

The energy spectrum of charge carriers in inhomogeneous metal oxide films is studied. The principle of specifying the potential on the boundary of nanomaterial/substrate, nanomaterial/atmosphere is demonstrated using the theory of fractals. The energy of the dimension quantization levels in the tin dioxide films with a fractal surface is numerically assessed.

A Simple Numerical Method for Determining the Energy Spectrum of Charge Carriers in Semiconductor Heterostructures

A simple numerical method for determining the energy spectrum and wave functions of charge carriers in semiconductor heterostructures (quantum wells, wires, dots, and superlattices) is proposed that employs the effective mass approximation in the general case of multiband kp Hamiltonian corresponding to the Γ point of the Brillouin zone. The method is based on the Fourier transform for structures with periodic potential. For single heterostructures, this periodicity is introduced artificially. In the framework of the proposed approach, the effective matrix Hamiltonian of a heterostructure can be written in two unitarily-equivalent a- and k-representations. As an example, single-band kp models of a heterostructure with one parabolic, triangular, or rectangular quantum well are considered and the influence of interfacial kp corrections on the behavior of envelope functions at sharp heteroboundaries is studied.

Energy Spectrum of Charge Carriers in Elastically Strained Assemblies of Ge/Si Quantum Dots

The results of studying the energy spectrum of electrons and holes localized in second-type Ge/Si heterostructures with Ge quantum dots are presented. In such structures, holes are localized at Ge quantum dots, and electrons, in three-dimensional quantum wells, which form in Si at the Ge—Si interface because of inhomogeneous deformations that appear as a result of the difference between the Ge and Si lattice constants. It is shown that changes in the deformations in the assembly of quantum dots as a result of a variation in their spatial arrangement significantly changes the binding energy of electrons, the position of their localization at quantum dots, the binding energy and wave-function symmetry of holes at double quantum dots (artificial molecules), and the exchange interaction of electrons and holes in the exciton composition. A practically important result of the presented data is the development of approaches to increase the luminescence quantum efficiency and the absorption coefficient in assemblies of quantum dots.

Suppression of Recombination in the Waveguide of a Laser Heterostructure by Means of Double Asymmetric Barriers

A semiconductor-laser design is proposed in which parasitic recombination in the waveguide region is suppressed by means of double asymmetric barriers adjacent to the active region. Double asymmetric barriers block the undesirable transport of one type of charge carrier while allowing the transport of the other type of carrier. The spacer in the double asymmetric barrier can serve to compensate the elastic strain introduced by the barrier layers as well as to control the energy spectrum of charge carriers and, thus, the transmission coefficient. By the example of a laser with Al0.2Ga0.8As waveguide layers, it is shown that the design with double asymmetric barriers makes it possible to suppress undesirable electron transport by a factor of 4 in comparison to the design using single asymmetric barriers.

Подавление волноводной рекомбинации за счет использования парных асимметричных барьеров в лазерных гетероструктурах

AbstractA semiconductor-laser design is proposed in which parasitic recombination in the waveguide region is suppressed by means of double asymmetric barriers adjacent to the active region. Double asymmetric barriers block the undesirable transport of one type of charge carrier while allowing the transport of the other type of carrier. The spacer in the double asymmetric barrier can serve to compensate the elastic strain introduced by the barrier layers as well as to control the energy spectrum of charge carriers and, thus, the transmission coefficient. By the example of a laser with Al_0.2Ga_0.8As waveguide layers, it is shown that the design with double asymmetric barriers makes it possible to suppress undesirable electron transport by a factor of 4 in comparison to the design using single asymmetric barriers.

Thermoelectric phenomena in layered conductors near the Lifshitz electron topological transition

This is a theoretical study of the response of an electron system to nonuniform heating of layered conductors with a quasi-two dimensional charge carrier energy spectrum near the Lifshitz electron topological transition when external interactions with the conductor, such as pressure, cause a change in the connectivity of the Fermi surface. With a variety of dispersion relations for the conduction electrons as examples, it is shown that there is a great variety of electronic topological transitions in layered conductors, which are accompanied by unusual magnetic field dependences of the kinetic coefficients. The migration of conduction electrons over different cavities (sheets) of the Fermi surface owing to magnetic breakdown is analyzed for close proximity of individual cavities of the Fermi surface. The dependence of the thermoelectric coefficients on the magnitude and orientation of strong magnetic fields B, such that the cyclotron frequency ωc is much higher than the collision frequency 1/τ of the conduction electrons, is calculated. An experimental study of these effects yields important information on the energy spectrum of the charge carriers.

Energy spectrum of charge carriers in TlIn1–x Yb x Te2 solid solutions

The temperature dependences of the electrical conductivity σ(T), the Hall coefficient R(T), and the thermoelectric coefficient α(T) are investigated in TlIn1–x Yb x Te2 (0 < x < 0.10) solid solutions at 80–1000К. From the kinetic parameters, the effective masses of electrons and holes are determined. The obtained experimental data on σ(T) and α(T) are interpreted within the context of a model with one and two types of charge carriers. It is established that, since x = 0.05, the TlIn1–x Yb x Te2 solid solutions belong to the class of narrow-gap semiconductors that have high matrix elements of interaction.

Effect of subband nonparabolicity on optical properties of InSbAs/AlSb deep quantum well heterostructures

Optical properties of heterostructures with deep quantum wells have been studied in the framework of four-band Kane mode permitting a nonparabolic energy spectrum of charge carriers to be taken into account. The system AlSb/InAs0.84Sb0.16/AlSb was used as an example. It is established that the nonparabolicity weakly influences the overlap integral between s- and p-states, but notably increase the state density and optical absorption coefficient in the conduction band.

Level anticrossing of impurity states in semiconductor nanocrystals.

The size dependence of the quantized energies of elementary excitations is an essential feature of quantum nanostructures, underlying most of their applications in science and technology. Here we report on a fundamental property of impurity states in semiconductor nanocrystals that appears to have been overlooked—the anticrossing of energy levels exhibiting different size dependencies. We show that this property is inherent to the energy spectra of charge carriers whose spatial motion is simultaneously affected by the Coulomb potential of the impurity ion and the confining potential of the nanocrystal. The coupling of impurity states, which leads to the anticrossing, can be induced by interactions with elementary excitations residing inside the nanocrystal or an external electromagnetic field. We formulate physical conditions that allow a straightforward interpretation of level anticrossings in the nanocrystal energy spectrum and an accurate estimation of the states' coupling strength.

The influence of the nonparabolic energy spectrum of charge carriers on the optical characteristics of AlSb/InAs0.84Sb0.16/AlSb heterostructures with deep quantum wells

The optical characteristics of heterostructures with deep quantum wells have been studied by the example of the AlSb/InAs0.84Sb0.16/AlSb system with allowance for a non-parabolic energy spectrum of charge carriers in the framework of the four-band Kane model. It is established that the nonparabolicity weakly influences the overlap integral between s and p states, but leads to a significant increase in the density of states in the conduction band and, in turn, to a considerable growth in the optical absorption coefficient.