arXiv subjects

V. Ya. Aleshkin

Publications and source records attributed to V. Ya. Aleshkin.

At least 19 recordsLinked to original sources

arXiv2026

Impact ionization in narrow band gap CdHgTe quantum well with "resonant" band structure

Impact ionization probabilities were calculated in a CdHgTe quantum well, where the distance between electron subbands is close to the band gap energy. This band structure enables impact ionization with small momentum transfer for electrons in the second subband. The study demonstrates that such processes increase the impact ionization probability by approximately two orders of magnitude compared to the impact ionization probability for electrons in the first subband, for which transitions with small momentum changes are impossible. The probability of single impact ionization during the electron energy loss due to optical phonon emission is estimated. Experimental methods for detecting impact ionization in this structure are discussed.

cond-mat.mtrl-sci↗

arXiv2023

Energy spectrum of valence band in HgTe quantum wells on the way from a two to the three dimensional topological insulator

The magnetic field, temperature dependence and the Hall effect have been measured in order to determine the energy spectrum of the valence band in HgTe quantum wells with the width (20-200)nm. The comparison of hole densities determined from the period Shubnikov-de Haas oscillations and the Hall effect shows that states at the top of valence band are double degenerate in teh entry quantum wells width the width range. The cyclotron mass determined from temperature dependence of SdH oscillations increases monotonically from (0.2-0.3) mass of the free electron, with increasing hole density from 2e11 to 6e11 cm^-2. The determined dependence has been compared to theoretical one calculate within the four band kp model. The experimental dependence was found to be strongly inconsistent with this predictions. It has been shown that the inclusion of additional factors (electric field, strain) does not remove the contradiction between experiment and theory. Consequently it is doubtful that the mentioned kp calculations adequately describe the valence band for any width of quantum well.

cond-mat.mes-hall↗

arXiv2021

Transformation of an energy spectrum and wave functions in the crossover from two- to three-dimensional topological insulator in HgTe quantum wells: long and thorny way

A magnetotransport and quantum capacitance of the two-dimensional electron gas in HgTe/Cd$_x$Hg$_{1-x}$Te quantum wells of a width ($20.2-46.0$)~nm are experimentally investigated. It is shown that the first energy subband of spatial quantization is split due to the spin-orbit interaction and the split branches are single-spin, therewith the splitting strength increases with the increase of the quantum well width. The electron effective masses in the branches are close to each other within the actual density range. Magneto-intersubband oscillations (MISO) observed in the structures under study exhibit the growing amplitude with the increasing electron density that contradicts to the expected decrease of wave function overlap for the rectangular quantum well. To interpret the data obtained, we have used a self-consistent approach to calculate the electron energy spectrum and the wave function within framework of the \emph{kP}-model. It has been in particular shown that the MISO amplitude increase results from the increasing overlap of the wave functions due to their shift from the gate electrode with the gate voltage increase known as phenomenon of the negative electron polarizability. The results obtained from the transport experiments are supported by quantum capacitance measurements.

cond-mat.mes-hall↗

arXiv2021

Stimulated emission of plasmon-LO mode in narrow gap HgTe/CdHgTe quantum wells

We calculate the dispersion of the plasmon-LO modes taking into account the spatial dispersion of the electronic polarizability. It is shown that stimulated emission of the plasmon-LO mode is possible in the frequency range corresponding to the Reststrahlen band of GaAs both in a 6 nm wide HgTe/CdTe QW and in a 5 nm wide HgTe/Cd0.7Hg0.3Te QW grown on the (013) plane. Due to the anisotropy of the dispersion law for the plasmon-LO mode, the [03-1] direction appears to be optimal for generation.

cond-mat.mes-hall↗

arXiv2020

Auger recombination in narrow band quantum well CdxHg1-xTe/CdyHg1-yTe heterostructures

We present detailed theoretical and experimental studies of Auger recombination in narrow-gap mercury cadmium telluride quantum wells (HgCdTe QWs). We calculate the Auger recombination probabilities as functions of non-equilibrium carrier density, temperature and composition of quantum wells taking into account the complex band dispersions and wave functions of the structures. Our theory is validated by comparison with measured kinetics of photoconductivity relaxation in QW with band gap of 76 meV at a temperature of 77 K. We find good agreement of theory and experiment using a single fitting parameter: the initial density of non-equilibrium carriers. The model is further used to optimize the composition of QWs and find the most suitable conditions for far-infrared lasing. Particularly, for band gap of 40 meV (lasing wavelength λ=31 μm) the lasing is favored in QWs with 6.5% cadmium fraction. We also find that at very large non-equilibrium carrier densities, the main recombination channel is associated with emission of two-dimensional plasmons and not with Auger process

cond-mat.mes-hall↗

arXiv2020

HgCdTe-based quantum cascade lasers operating in the GaAs phonon Reststrahlen band predicted by the balance equations method

HgCdTe-based quantum cascade lasers operating in the GaAs phonon Reststrahlen band with a target wavelength of 36 mkm are theoretically investigated using the balance equations method. The optimized active region designs, which are based on three and two quantum wells, exhibit a peak gain exceeding 100 cm(-1) at 150 K. We analyze the temperature dependences of the peak gain and predict the maximum operation temperatures of 170 K and 225 K for three- and two-well designs, respectively. At high temperatures (T > 120 K), the better temperature performance of the two-well design is associated with a larger spatial overlap of the weakly localized lasing wavefunctions as well as a higher population inversion.

physics.app-ph↗

arXiv2019

Aniotropy of in-plane g-factor of electrons in HgTe quantum wells

The results of experimental studies of the Shubnikov-de Haas (SdH) efect in the (013)-HgTe/Hg$_{1-x}$Cd$_x$Te quantum wells (QWs) of electron type of conductivity both with normal and inverted energy spectrum are reported. Comprehensive analysis of the SdH oscillations measured for the different orientations of magnetic field relative to the quantum well plane and crystallographic exes allows us to investigate the anisotropy of the Zeeman effect. For the QWs with inverted spectrum, it has been shown that the ratio of the spin splitting to the orbital one is strongly dependent not only on the orientation of the magnetic field relative to the QW plane but also on the orientation of the in-plane magnetic field component relative to crystallographic axes laying in the QW plane that implies the strong anisotropy of in-plane g-factor. In the QW with normal spectrum, this ratio strongly depends on the angle between the magnetic field and the normal to the QW plane and reveals a very slight anisotropy in the QW plane. To interpret the data, the Landau levels in the tilted magnetic field are calculated within the framework of four-band \emph{kP} model. It is shown that the experimental results can be quantitatively described only with taking into account the interface inversion asymmetry.

cond-mat.mes-hall↗

arXiv2019

Negative polarizability of 2D electrons in HgTe quantum well

The polarizability of electrons occupying the lowest subband of spatial quantization in CdTe/Cd$_x$Hg$_{1-x}$Te/CdTe quantum wells is calculated. It is shown that polarizability in the quantum well without cadmium is negative, i.e., the displacement of an electron in an electric field applied perpendicularly to the quantum well plane is opposite to the force acting on it. The negative polarizability of 2D electrons can reduce the dielectric constant of quantum wells by up to $(10-15)$ percent.

cond-mat.mes-hall↗

arXiv2019

Amplification of surface plasmons in graphene-black phosphorus injection laser heterostructures

We propose and evaluate the heterostructure based on the graphene-layer (GL) with the lateral electron injection from the side contacts and the hole vertical injection via the black phosphorus layer (PL) (p$^+$PL-PL-GL heterostructure). Due to a relatively small energy of the holes injected from the PL into the GL (about 100 meV, smaller than the energy of optical phonons in the GL which is about 200 meV), the hole injection can effectively cool down the two-dimensional electron-hole plasma in the GL. This simplifies the realization of the interband population inversion and the achievement of the negative dynamic conductivity in the terahertz (THz) frequency range enabling the amplification of the surface plasmon modes. The later can lead to the plasmon lasing. The conversion of the plasmons into the output radiation can be used for a new types of the THz sources.

cond-mat.mes-hall↗

arXiv2018

Spin-orbit splitting of the conduction band in HgTe quantum wells: role of different mechanisms

Spin-orbit splitting of conduction band in HgTe quantum wells was studied experimentally. In order to recognize the role of different mechanisms, we carried out detailed measurements of the Shubnikov-de Haas oscillations in gated structures with a quantum well widths from $8$ to $18$ nm over a wide range of electron density. With increasing electron density controlled by the gate voltage, splitting of the maximum of the Fourier spectrum $f_0$ into two components $f_1$ and $f_2$ and the appearance of the low-frequency component $f_3$ was observed. Analysis of these results shows that the components $f_1$ and $f_2$ give the electron densities $n_1$ and $n_2$ in spin-orbit split subbands while the $f_3$ component results from magneto-intersubband oscillations so that $f_3=f_1 - f_2$. Comparison of these data with results of self-consistent calculations carried out within the framework of four-band \emph{kP}-model shows that a main contribution to spin-orbit splitting comes from the Bychkov-Rashba effect. Contribution of the interface inversion asymmetry to the splitting of the conduction band turns out to be four-to-five times less than that for the valence band in the same structures.

cond-mat.mtrl-sci↗

arXiv2018

Renormalization of the conduction band spectrum in HgTe quantum wells by electron-electron interaction

The energy spectrum of the conduction band in HgTe/Cd$_x$Hg$_{1-x}$Te quantum wells of a width $d=(4.6-20.2)$ nm has been experimentally studied in a wide range of electron density. For this purpose, the electron density dependence of the effective mass was measured by two methods: by analyzing the temperature dependence of the Shubnikov-de Haas oscillations and by means of the quantum capacitance measurements. There was shown that the effective mass obtained for the structures with $d (7-8)$ nm, the experimental effective mass becomes noticeably less than the calculated ones. This difference increases with the electron density decrease, i.e., with lowering the Fermi energy; the maximal difference between the theory and experiment is achieved at $d = (15-18)$ nm, where the ratio between the calculated and experimental masses reaches the value of two and begins to decrease with a further $d$ increase. We assume that observed behavior of the electron effective mass results from the spectrum renormalization due to electron-electron interaction.

cond-mat.mtrl-sci↗

arXiv2018

Landau level spectroscopy of valence bands in HgTe quantum wells: Effects of symmetry lowering

Landau level spectroscopy has been employed to probe the electronic structure of the valence band in a series of p-type HgTe/HgCdTe quantum wells with both normal and inverted ordering of bands. We find that the standard axial-symmetric 4-band Kane model, which is nowadays widely applied in physics of HgTe-based topological materials, does not fully account for the complex magneto-optical response observed in our experiments - notably, for the unexpected avoided crossings of excitations and for the appearance of transitions that are electric-dipole forbidden within this model. Nevertheless, reasonable agreement with experiments is achieved when the standard model is expanded to include effects of bulk and interface inversion asymmetries. These remove the axial symmetry, and among other, profoundly modify the shape of valence bands.

cond-mat.mes-hall↗

arXiv2018

Interband infrared photodetectors based on HgTe--CdHgTe quantum-well heterostructure

We calculate the characteristics of interband HgTe-CdHgTe quantum-well infrared photodetectors (QWIPs). Due to a small probability of the electron capture into the QWs, the interband HgTe-CdHgTe QWIPs can exhibit very high photoconductive gain. Our analysis demonstrates significant potential advantages of these devices compared to the conventional CdHgTe photodetectors and the A$_3$B$_5$ heterostructures.

cond-mat.mtrl-sci↗

arXiv2017

The valence band energy spectrum of HgTe quantum wells with inverted band structures

The energy spectrum of the valence band in HgTe/Cd$_x$Hg$_{1-x}$Te quantum wells with a width $(8-20)$~nm has been studied experimentally by magnetotransport effects and theoretically in framework $4$-bands $kP$-method. Comparison of the Hall density with the density found from period of the Shubnikov-de Haas (SdH) oscillations clearly shows that the degeneracy of states of the top of the valence band is equal to 2 at the hole density $p< 5.5\times 10^{11}$~cm$^{-2}$. Such degeneracy does not agree with the calculations of the spectrum performed within the framework of the $4$-bands $kP$-method for symmetric quantum wells. These calculations show that the top of the valence band consists of four spin-degenerate extremes located at $k\neq 0$ (valleys) which gives the total degeneracy $K=8$. It is shown that taking into account the "mixing of states" at the interfaces leads to the removal of the spin degeneracy that reduces the degeneracy to $K=4$. Accounting for any additional asymmetry, for example, due to the difference in the mixing parameters at the interfaces, the different broadening of the boundaries of the well, etc, leads to reduction of the valleys degeneracy, making $K=2$. It is noteworthy that for our case two-fold degeneracy occurs due to degeneracy of two single-spin valleys. The hole effective mass ($m_h$) determined from analysis of the temperature dependence of the amplitude of the SdH oscillations show that $m_h$ is equal to $(0.25\pm0.02)\,m_0$ and weakly increases with the hole density. Such a value of $m_h$ and its dependence on the hole density are in a good agreement with the calculated effective mass.

cond-mat.mtrl-sci↗

arXiv2014

Graphene vertical cascade interband terahertz and infrared photodetectors

We propose and evaluate the vertical cascade terahertz and infrared photodetectors based on multiple-graphene-layer (GL) structures with thin tunnel barrier layers (made of tungsten disulfide or related materials). The photodetector operation is associated with the cascaded radiative electron transitions from the valence band in GLs to the conduction band in the neighboring GLs (interband- and inter-GL transitions). We calculate the spectral dependences of the responsivity and detectivity for the vertical cascade interband GL- photodetectors (I-GLPDs) with different number of GLs and doping levels at different bias voltages in a wide temperature range. We show the possibility of an effective manipulation of the spectral characteristics by the applied voltage. The spectral characteristics depend also on the GL doping level that opens up the prospects of using I-GLPDs in the multi-color systems. The advantages of I-GLPDs under consideration are associated with their sensitivity to the normal incident radiation, weak temperature dependence of the dark current as well as high speed of operation. The comparison of the proposed I-GLDs with the quantum-well intersubband photodectors demonstrates the superiority of the former, including a better detectivity at room temperature and a higher speed. The vertical cascade I-GLDs can also surpass the lateral p-i-n GLDs in speed.

cond-mat.mes-hall↗

arXiv2013

Injection terahertz laser using the resonant inter-layer radiative transitions in double-graphene-layer structure

We propose and substantiate the concept of terahertz (THz) laser enabled by the resonant electron radiative transitions between graphene layers (GLs) in double-GL structures. We estimate the THz gain for TM-mode exhibiting very low Drude absorption in GLs and show that the gain can exceed the losses in metal-metal waveguides at the low end of the THz range. The spectrum of the emitted photons can be tuned by the applied voltage. A weak temperature dependence of the THz gain promotes an effective operation at room temperature.

cond-mat.mes-hall↗

arXiv2012

Quantum well-based waveguide for semiconductor lasers

In this work we study a possibility of waveguide fabrication on the basis of active quantum wells in semiconductor lasers. The efficiency of such a waveguide for an InP structure with In0.53Ga0.47As quantum wells is demonstrated experimentally. An optically-pumped laser on this basis is realized.

physics.optics↗

arXiv2009

Feasibility of terahertz lasing in optically pumped epitaxial multiple graphene layer structures

A multiple-graphene-layer (MGL) structure with a stack of GLs and a highly conducting bottom GL on SiC substrate pumped by optical radiation is considered as an active region of terahertz (THz) and far infrared (FIR) lasers with external metal mirrors. The dynamic conductivity of the MGL structure is calculated as a function of the signal frequency, the number of GLs, and the optical pumping intensity. The utilization of optically pumped MGL structures might provide the achievement of lasing with the frequencies of about 1 THz at room temperature due to a high efficiency.

cond-mat.mes-hall↗