Showing papers in "Semiconductors in 2020"

Manganese-Doped ZnS QDs: an Investigation into the Optimal Amount of Doping

Abstract: In the present study, undoped and Mn-doped ZnS, Zn1 – xMnxS (x = 0, 0.02, 0.06, 0.10) quantum dots (QDs) were successfully synthesized using the simple co-precipitation method. The synthesized samples were thoroughly studied using X-ray diffraction (XRD), UV-visible absorption, high-resolution transmission electron microscopy (HRTEM) with selected area of the electron diffraction, scanning electron microscope with energy dispersive X-ray spectra, photoluminescence emission (PLE), and Fourier transform infrared spectroscopy. The XRD pattern confirmed the cubic zinc-blende phase at low doping concentration; however, at higher Mn-doping concentration hetaerolite phase formation was observed. The calculated particle size using Debye–Scherrer relation was found between 1.90–2.35 nm, which was also confirmed by HRTEM analysis. The blue shift in the absorption peak of all the prepared ZnS QDs as compared to bulk ZnS was indicative of the formation of nanoparticles and the calculated band gap was in the range of 3.94–4.11 eV. The PLE spectroscopy of the synthesized QDs was performed at the excitation wavelength of 280 nm and corresponding emission spectroscopy confirmed the surface defects in synthesized ZnS QDs.

Solar-Blind UV Detectors Based on β-Ga2O3 Films

Abstract: Resistive-type structures based on gallium-oxide films are studied. The Ga2O3 films are produced by radio-frequency magnetron-assisted sputtering of a β-Ga2O3 (99.9999%) target onto unheated sapphire substrates with preliminarily deposited platinum electrodes. The data on the structure and phase composition of the films are obtained immediately after sputtering and after annealing in argon at 900°C for 30 min. The current–voltage characteristics are recorded in the dark and upon exposure to radiation at the wavelength λ = 254 nm. It is shown that, after annealing, the photocurrent increases by an order of magnitude. The lack of sensitivity of the structures to radiation in the visible wavelength region (λ = 400 nm) is verified experimentally.

First Principles Study on Electronic Structure and Optical Properties of Ternary Semiconductor InxAl1 –xP Alloys

Abstract: The elastic, electronic and optical properties of the indium doped AlP, have been investigated by the first-principle calculations within the framework of the density functional theory (DFT). Our calculated lattice constants and bulk moduli for AlP and InP are in good agreement with the available theoretical and experimental data. The lattice constants increase while the bulk modulus decreases with In concentration increasing. The elastic constants Cij of InxAl1 –xP alloys have been calculated for the first time. Result shows that with the increase of indium concentration, the band gap of InxAl1 –xP decreases and varies from indirect band gap to direct band gap; the absorption band edge and the absorption peak move to low energy side; the static reflectivity increases. With the increasing of the incident photon energy, InxAl1 –xP shows metal reflective properties in certain energy range. With the increasing of Indium concentration, static dielectric constant increases and the intersection of dielectric function and the x-axis move towards low energy side; the peak of energy loss function move to high energy side and the peak value reduces.

TCAD Simulation Study of Single-, Double-, and Triple-Material Gate Engineered Trigate FinFETs

Abstract: A detailed comparative performance analysis of the Trigate Fin Field Effect Transistor (FinFET) device with different structures such as Single-Material Gate (SMG) FinFET, Double-Material Gate (DMG) FinFET, and Triple-Material Gate (TMG) FinFET has been done. Silvaco Atlas Technology Computer-Aided Design (TCAD) tool is used to model the Trigate FinFET device structures and to characterize all the electrical parameters of the device. The simulation results confirm that TMG FinFET device structure shows better performance than SMG and DMG FinFET device structures, in terms of device electrical parameters such as surface potential, electric field, and drain current. Moreover, TMG FinFET device structure exhibits an excellent transconductance of 0.28 μA/V when compared with SMG FinFET (0.21 μA/V) and DMG FinFET (0.24 μA/V).

Band Gap Opening of Doped Graphene Stone Wales Defects: Simulation Study

Abstract: We implemented density functional theory to investigate the electronic properties of doped graphene Stone Wales defects. We found that the band gap of nitrogen doped graphene with different orientations of Stone Wales defect could be tuned. The obtained band gap results strongly depend not only on the specific location of the doped atom, but also on the orientations of Stone Wales defects. The symmetrical density of states is an indication that the total magnetic moment was zero as the valence electrons grouped in pairs. In addition, we performed charge analysis for all nitrogen doped graphene Stone Wales defects structures and it can be observed that the carbon atoms are more electronegative compared to nitrogen atoms, which obtain all the valence electrons. The transferred charge from nitrogen atom is largely localized on the carbon atoms lying in close proximity of the dopant atom.

Effective Mass Model Supported Band Gap Variation in Cobalt-Doped ZnO Nanoparticles Obtained by Co-Precipitation

Abstract: Zn1 –xCoxO (x = 0, 0.01, 0.03, 0.05) nanoparticles were synthesized using co-precipitation method. Shift in peaks of XRD patterns for 2θ values has been observed. The changes in 2θ value for different peaks for different samples are studied systematically. Dislocation densities (δ) for the samples are calculated and correlated with observed shift in 2θ values for all the samples. UV-Vis study has been performed to understand the effect of cobalt doping on optical band gap. The band gap shows a cubic variation with dopant concentration (x). The nature of band gap variation has been explained and supported by effective mass model. Samples are also characterized by SEM and EDX to understand the surface morphology and elemental composition.

Modification of the Atomic and Electronic Structure of III–V Semiconductor Surfaces at Interfaces with Electrolyte Solutions (Review)

Abstract: Recent experimental and theoretical data on modification of the atomic and electronic structures of the surface of different III–V semiconductors by electrolyte solutions are reviewed. The interrelation between chemical reactions occurring at semiconductor/electrolyte interfaces, the charge transfer between the semiconductor and the solution, and corresponding modifications of the atomic and electronic structures of the semiconductor surface is established. Examples of modification of the electronic characteristics and properties of semiconductor devices and nanostructures under interaction with electrolyte solutions are given.

Structure of Germanium Monoxide Thin Films

Abstract: By optical methods (Raman spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy) and electron-microscopy techniques, it was found that the atomic structure of germanium monoxide films of stoichiometric composition corresponds to the random bonding model and does not contain germanium nanoclusters. This structure is metastable and transforms into a random mixture structure at a temperature of 260°C and higher. The metastability of solid GeO can be caused by internal strains in the atomic network.

Structural and Photoluminescence Properties of Graphite-Like Carbon Nitride

Abstract: Interrelationship between the structure and optical properties of graphite-like semiconductor carbon nitride produced by the heat treatment of thiocarbamide in an oxygen-containing medium at temperatures in the range from 400°C to 625°C is established. It is found that the maximum of the photoluminescence band shifts from 417 to 494 nm and simultaneously broadens, as the temperature of synthesis is elevated to 625°C. This effect is attributed to doping with oxygen and to the formation of defects as a consequence of decomposition of the already synthesized material with increasing temperature.

Investigation of the Influences of Post-Thermal Annealing on Physical Properties of TiO2 Thin Films Deposited by RF Sputtering

Abstract: For this study, titanium dioxide (TiO2) thin films were deposited on glass substrates at room temperature by the RF magnetron sputtering technique. The preparation parameters that offer better control and reproducibility of film fabrication were first optimized. Then, the effects of post-deposition annealing temperature at 350, 450, and 550°C on the microstructure, surface morphology, and optical properties of the prepared films were investigated using X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV–Visible (UV–Vis) spectrophotometry. Interestingly, XRD analysis shows that as-deposited and annealed TiO2 film possess anatase crystal structure only with a preferential orientation along the (101) plane. The intensity of the (101) diffraction peak and crystallite size are found to increase with increasing annealing temperature, which indicates an improvement in the crystallinity of the films. Raman spectra confirm that all samples possess anatase phase and the crystallinity is enhanced with increasing thermal annealing. From the analysis of SEM and AFM images, it is revealed that the heat treatment significantly affects the morphology, grain size, and surface roughness of the TiO2 films. The UV–Vis spectroscopy analysis shows that as-deposited TiO2 thin film is highly transparent in the visible region with an average transmittance about 84%, whereas the transmission decreases slightly with an increase in annealing temperature. Moreover, the optical band gap energy shows a red shift with increasing the annealing temperature.

Dual Material Gate Engineering to Reduce DIBL in Cylindrical Gate All Around Si Nanowire MOSFET for 7-nm Gate Length

Abstract: In this work, drain current ID for 7-nm gate length dual-material (DM) cylindrical gate all around (CGAA) silicon nanowire (SiNW) has been studied and simulation results are reported using Silvaco ATLAS 3D TCAD. In this device, we consider the non-equilibrium Green’s function (NEGF) approach and self-consistent solution of Schrodinger's equation with Poisson’s equation. The splitting of conduction in multiple sub-bands has been considered and there is no doping in the channel region. The effect of DM gate engineering (variation of screen gate and control gate length having different work function) for SiNW channel with 2-nm radius and gate oxide (SiO2) thickness of 0.8 nm on ID have been studied. It was found that DM gate engineering reduces drain-induced barrier lowering (DIBL) but it also slightly increases sub-threshold slope (SS). This work has obtained small DIBL (~54 mV/V), small SS (~68 mV/dec), and higher IOn/IOff (~4 × 108) ratio as compared to literature concerning the inversion mode devices. The smallest DIBL is obtained when control gate length is the highest, and vice versa. With increase in control gate length, there is also increase in both IOn and IOff but IOn/IOff ratio decreases.

Light Characteristics of Narrow-Stripe High-Power Semiconductor Lasers (1060 nm) Based on Asymmetric AlGaAs/GaAs Heterostructures with a Broad Waveguide

Abstract: The emission characteristics of narrow mesa-stripe (5.5 μm) lasers based on asymmetric AlGaAs/GaAs heterostructures are studied. It is shown that the maximum optical power achieved in the continuous-wave (CW) operation mode is limited by heating and reaches a value of 1695 mW at a current of 2350 mA at +25°C, with the maximum efficiency reaching 54.8%. Reducing the working temperature to –8°C makes it possible to raise the maximum low-mode CW power to 2 W. A peak power of 2930 mW is obtained under pumping with current pulses (width 240 ns, amplitude 4230 mA). It is shown that the power profile has in the pulsed mode an “optical dip” region in which low-efficiency lasing occurs with the generation of a train of subnanosecond pulses.

Study of the Properties of Two-Dimensional MoS2 and WS2 Films Synthesized by Chemical-Vapor Deposition

Abstract: Molybdenum- and tungsten-disulfide films are synthesized by chemical-vapor deposition. The set of optimal synthesis parameters (temperature, time, and amount and ratio of precursors) is established at which MoS2 domains with maximum lateral sizes of up to 250 μm on sapphire and MoS2 and WS2 domains up to 80 μm in size on SiO2 can be grown. Domain intergrowth leads to the formation of homogeneous single-layer MoS2 films. The Raman spectra of the synthesized films contain two characteristic peaks corresponding to the atomic vibrations in MoS2 and WS2. Photoluminescence of the single-layer and bilayer MoS2 films with a maximum intensity of 670 ± 2 nm and of the single-layer WS2 films with a maximum intensity of 630 ± 2 nm is detected. The photoluminescence spectral maps (the dependences of the photoluminescence intensity on the luminescence and excitation-light wavelengths) are measured. According to the measured data, the photoluminescence excitation spectrum of MoS2 has a maximum at 350 ± 5 nm and the photoluminescence excitation spectrum of WS2 has a maximum at 330 ± 5 nm. The I–V characteristics of the synthesized films are photosensitive in the visible spectral range.

On the Pulsed-Laser Deposition of Bismuth-Telluride Thin Films on Polyimide Substrates

Abstract: The peculiarities of obtaining p-Bi0.5Sb1.5Te3 and n-Bi2Te2.7Se0.3 thin thermoelectric films with a thickness of about 300 nm grown on a polyimide substrate by the pulsed-laser-deposition method are reported. The influence of the growth temperature, pressure and target-to-substrate distance on the film’s thermoelectric properties is investigated. Thermoelectric p- and n-type films exhibit a high Seebeck coefficient of 220 and –200 μV/K and low electrical power factors of 9.7 and 5.0 μW/(cm K2) respectively due to the relatively high electrical resistances of the films.

Effect of the Beryllium Acceptor Impurity upon the Optical Properties of Single-Crystal AlN

Abstract: The influence of the high-temperature (T = 1880°C) diffusion of beryllium ions on the properties of single-crystal aluminum nitride is studied. It is shown that the postgrowth doping of AlN with Be brings about the compensation of shallow Si donor centers uncontrollably incorporated into the AlN lattice during growth. It is established that the introduction of Be into the AlN lattice results in a reduction in the optical absorption of AlN in the visible and ultraviolet regions. The set of results is attributed to a shift of the Fermi level to the top of the valence band of AlN upon the introduction of the Be acceptor impurity.

Structure, Optical, and Photoelectric Properties of Lead-Sulfide Films Doped with Strontium and Barium

Abstract: Evolution of the morphology, composition, structural characteristics (lattice constant, microstrains, texturing), and optical and photoelectric properties of PbS films produced by chemical bath deposition in the presence of ammonium iodide and strontium or barium chlorides at a concentration up to 5 mM is studied. According to the data of energy dispersive X-ray analysis, the content of strontium in the PbS films is 0.4–0.7 at %, whereas the content of barium is beyond the determination error. The size of the particles forming the films varies from ~200 to ~400 nm, and the size distribution of the particles is monomodal. The introduction of NH4I and SrCl2 or BaCl2 into the reactor retains the B1 cubic structure of lead sulfide, but gives rise to an unsteady change in the lattice parameter, which is due to the creation of vacancy-type or interstitial ion defects. The introduction of salts of strontium or barium does not influence the band gap, but changes the intensities of the impurity absorption bands deep in the band gap or near the bottom of the conduction band. The dependences of the volt–watt sensitivity of the films on the content of salts of strontium and barium are of an extreme character and show maxima at 0.05 and 0.1 mM, respectively.

Two-Stage Synthesis of Structured Microsystems Based on Zinc-Oxide Nanorods by Ultrasonic Spray Pyrolysis and the Low-Temperature Hydrothermal Method

Abstract: The specific features are presented of the two-stage synthesis of structured microsystems based on zinc-oxide nanorods by ultrasonic spray pyrolysis and the low-temperature hydrothermal method, with nucleation suppressed in the bulk of the solution. It is shown that the use of two-stage synthesis provides control over the size and aspect ratio of separate nanorods and over the structure of the microsystem of nanorods as a whole. It is proposed to monitor the concentration of intrinsic surface defects by measuring the photocurrent under irradiation through narrow-band interference light filters.

Investigation of the Magnesium Impurity in Silicon

Abstract: The diffusion profiles of the concentration of electrically active and total concentrations of the magnesium impurity in silicon are measured. Diffusion is carried out by the sandwich method into FZ dislocation-free n-type silicon at the temperatures Tdiff = 1000 and 1100°C, and at a process duration from 0.5 to 22.5 h. The concentration profiles $${{N}_{{{\text{M}}{{{\text{g}}}_{i}}}}}$$(x) of the electrically active magnesium component are determined by the differential-conductivity method, and the total-concentration profiles Ntotal(x), by secondary-ion mass spectroscopy. It is established that the total concentration of magnesium in the samples is ~2 orders of magnitude higher than that of the electrically active component. It is also found that the diffusion coefficient $${{D}_{{{\text{M}}{{{\text{g}}}_{i}}}}}$$ of interstitial magnesium depends on the diffusion time and decreases with an increase in the duration of the process. Assumptions are made about the physical processes, which can lead to the formation of an electrically inactive component of magnesium impurity and to the dependence of the effective diffusion coefficient on time.

Influence of Radiation Defects Induced by Low-Energy Protons at a Temperature of 83 K on the Characteristics of Silicon Photoelectric Structures

Abstract: Irradiation by low-energy products leads to a variation in the electrical, optical, and other properties of the surface layer of semiconductor structures, which gives additional possibilities to modify semiconductor devices. This work is devoted to investigating the influence of radiation defects induced by low-energy protons at a sample temperature of 83 K on the properties of double-sided silicon photoelectric structures with a diffusion n+–p junction. Samples of the n+–p–p+ type are irradiated by a proton flux with a dose of 1015 cm–2 and energy of 40 or 180 keV. To explain the observed regularities of varying the parameters of the current–voltage characteristics and transmission coefficients, the distribution of the average number of interstitial silicon, vacancies, divacancies, and disordered regions formed under these conditions per length unit of the projected path by one proton in the diffusion layer in the space-charge region of the n+–p junction is calculated. It is shown that protons with an initial energy of 40 keV preferentially vary the physical properties of the layer with a high concentration of donors, while protons with an initial energy of 180 keV vary the properties of the space-charge region in the layer containing acceptors. The number of radiation-induced defects at the maximum of the spatial distribution in the n-type region is much smaller than in the p-type region.

Fabrication and Analysis of the Current Transport Mechanism of Ni/n-GaN Schottky Barrier Diodes through Different Models

Abstract: The current transport mechanism of indigenously fabricated Ni/n-GaN Schottky barrier diodes (SBDs) has been analysed using the current–voltage (I–V) and capacitance–voltage (C–V) measurements. Various models like Rhoderick’s method, Cheung’s method, Norde’s method, modified Norde’s method, Hernandez’s method, and Chattopadhyay’s method have been used to extract the different electric parameters from the I–V curve. A comparison has been made between the various electrical parameters such as ideality factor, barrier height, and series resistance, which are extracted from the forward bias I–V curve of Ni/n-GaN SBDs. The carrier concentration of the substrate and the barrier height is obtained from C–V characteristics of Ni/n-GaN SBDs. We observe from the reverse current characteristics that the Ni/n-GaN SBDs show the dominance of Schottky emission in intermediate and higher voltages.

Hydrothermal Growth of Undoped and Zn-Doped SnO Nanocrystals: A Frequency Dependence of AC Conductivity and Dielectric Response Studies

Abstract: The aim of this work is to investigate the dielectric properties of undoped and Zn-doped Tin monoxide (SnO) nanocrystals synthesized by the hydrothermal technique. The prepared nanocrystals were made as pellet and characterized by using the LCR meter at various temperatures range from 313 to 373 K for undoped samples and at room temperature for Zn-doped samples in the frequency ranging from 50 Hz to 20 kHz and 50 Hz to 1 MHz respectively. The increase in measurement temperatures of undoped samples reveals the increase in dielectric constant in accordance with the frequency. The activation energy of 0.58 meV has calculated using the Arrhenius plot of DC conductivity at various temperatures. The dielectric loss and dielectric constant values were decreased with the increasing Zn doping concentration but the ac electrical conductivity increases as a function of frequency and also decreases with respect to dopant concentration.

Molecular States of Composite Fermions in Self-Organized InP/GaInP Quantum Dots in Zero Magnetic Field

Abstract: The size and positions of regions of line localization and the magnetic-field (0–10 T) dependence of the low-temperature (10 K) photoluminescence spectra of single InP/GaInP quantum dots with a number of electrons of N = 5–7 and a Wigner–Seitz radius of ~2.5 are determined using a near-field scanning optical microscope. The formation of composite fermion molecules with a size coinciding with that of localization regions and bond lengths of ~30 and 50 nm, respectively, at a Landau-level filling factor from 1/2 to 2/7 in zero magnetic field is established. At N = 6, the pairing and rearrangement of composite fermions under photoexcitation are found, which offers opportunities for the use of InP/GaInP quantum dots to create a magnetic-field-free topological quantum gate.

Conductance Quantization in Memristive Structures Based on Poly-p-Xylylene

Abstract: The results of studying the room-temperature conductance quantization of memristive structures based on poly-p-xylylene organic material with resistive switching are presented. The measurement procedures are shown and comparative analysis of manifestation of the effect upon switching structures to the high and low resistive states is presented. The possibility of specifying the stable quantum states of the conductance in memristive structures based on poly-p-xylylene is demonstrated. It is shown that some of these states possess short-term stability, while others possess long-term stability. These results open up new possibilities for using the conductance quantization effect in the implementation of neuromorphic systems.

Fabrication of a Ge–GeS:Nd Heterojunction and Investigation of the Spectral Characteristics

Abstract: The technology of producing a Ge–GeS:Nd heterojunction and the relative spectral characteristics of the quantum efficiency of the fabricated heterojunction are investigated at different γ-irradiation doses. It is found that the photosensitivity increases at a dose of 30 krad in the spectral range of 0.4–2.0 μm. With increasing the radiation dose to 100 krad, the heterojunction photosensitivity decreases significantly.

Luminescence of Spatially Ordered Self-Assembled Solitary Ge(Si) Nanoislands and their Groups Incorporated into Photonic Crystals

Abstract: The luminescence properties of arrays of spatially ordered self-assembled solitary Ge(Si) nanoislands and their groups, including those embedded in two-dimensional photonic crystals, are studied. It is shown that the incorporation of an array of ordered solitary Ge(Si) islands and their groups into photonic crystals results in an increase in the intensity of their photoluminescence signal at liquid-nitrogen temperature. The maximum increase in the intensity (by a factor of up to ~30) is observed for an ordered array of solitary Ge(Si) islands. The increase in the intensity is attributed to the interaction of emission from islands with photonic-crystal radiative modes. This interaction is more efficient in the case of an array of solitary islands. Due to such interaction the luminescence signal from ordered solitary Ge(Si) islands incorporated into photonic crystals is observed at up to room temperature.

On the Formation of Amorphous Ge Nanoclusters and Ge Nanocrystals in GeSixOy Films on Quartz Substrates by Furnace and Pulsed Laser Annealing

Abstract: Nonstoichiometric GeO0.5[SiO2]0.5 and GeO0.5[SiO]0.5 germanosilicate glassy films are produced by the high-vacuum coevaporation of GeO2 and either SiO or SiO2 powders with deposition onto a cold fused silica substrate. Then the films are subjected to furnace or laser annealing (a XeCl laser, λ = 308 nm, pulse duration of 15 ns). The properties of the samples are studied by transmittance and reflectance spectroscopy, Raman spectroscopy, and photoluminescence spectroscopy. As shown by analysis of the Raman spectra, the GeO[SiO] film deposited at a substrate temperature of 100°C contains amorphous Ge clusters, whereas no signal from Ge–Ge bond vibrations is observed in the Raman spectra of the GeO[SiO2] film deposited at the same temperature. The optical absorption edge of the as-deposited GeO[SiO2] film corresponds to ~400 nm; at the same time, in the GeO[SiO] film, absorption is observed right up to the near-infrared region, which is apparently due to absorption in Ge clusters. Annealing induces a shift of the absorption edge to longer wavelengths. After annealing of the GeO[SiO2] film at 450°C, amorphous germanium clusters are detected in the film, and after annealing at 550°C as well as after pulsed laser annealing, germanium nanocrystals are detected. The crystallization of amorphous Ge nanoclusters in the GeO[SiO] film requires annealing at a temperature of 680°C. In this case, the size of Ge nanoclusters in this film are smaller than that in the GeO[SiO2] film. It is not possible to crystallize Ge clusters in the GeO[SiO] film. It seems obvious that the smaller the semiconductor nanoclusters in an insulating matrix, the more difficult it is to crystallize them. In the low-temperature photoluminescence spectra of the annealed films, signals caused by either defects or Ge clusters are detected.

Energy-Gap Opening Near the Dirac Point after the Deposition of Cobalt on the (0001) Surface of the Topological Insulator BiSbTeSe2

Abstract: It is shown for the first time that Co subnanometer coatings deposited by molecular-beam epitaxy on the (0001) surface of the topological insulator BiSbTeSe2 at a temperature of 330°C open an energy gap in the spectrum of topological surface states in the region of the Dirac point with a shift of the Dirac-point position caused by the preliminary deposition of an adsorbate at room temperature. The gap width is 21 ± 6 meV. Temperature-dependent measurements in the range of 15–150 K show no changes in the energy-gap width.

Hydrodynamic Terahertz Plasmons and Electron Sound in Graphene with Spatial Dispersion

Abstract: The intrinsic transverse-magnetic modes of graphene with spatial dispersion are investigated theoretically in the hydrodynamic regime in a terahertz frequency range. It is revealed that spatial dispersion is caused by the diffusion electron-transport mechanism due to the spreading of electron-concentration gradients under the effect of pressure in an electron liquid. The cases of a screened and unscreened plasmon as well as electron sound are considered.

Double-Channel Electron Transport in Suspended Quantum Point Contacts with in-Plane Side Gates

Abstract: The conductance of a suspended quantum point contact fabricated on the basis of GaAs/AlGaAs heterostructures with a two-dimensional electron gas and equipped with side gates separated from the constriction using lithographical trenches is investigated. The gate dependences of the conductance of such structures correspond to the unusual double-channel mode with independent quantization of the conductance of two channels, and the conductance of separate channels can be independently controlled using two side gates. The electrostatic-formation mechanism of a two-channel structure inside a single constriction associated with the lateral redistribution of low-mobility X-valley electrons containing superlattice heterostructure layers, which leads to the formation of a potential barrier separating the conductivity electrons into two channels symmetrically shifted towards the lithographic trenches, specifying the nanostructure geometry, is considered.

On the Dominant Mechanism of the Nonradiative Excitation of Manganese Ions in II-VI Diluted Magnetic Semiconductors

Abstract: Doping II–VI semiconductors and low-dimensional structures based on them by manganese leads to the effective quenching of electroluminescence and photoluminescence under the condition that the electron excitation energy of the crystal exceeds the energy of the intracenter transition of the Mn2+ ion EMn ≈ 2.1 eV. Quenching implies effective energy transfer from a photoexcited crystal to Mn2+ ions. Three mechanisms of such nonradiative energy transfer are possible, notably, the dipole–dipole mechanism, the exchange mechanism, and a mechanism related to the latter, which is associated with sp–d mixing. Although it is thought that the dipole–dipole mechanism is not particularly efficient because of the forbidden intracenter transition for Mn2+, while the dominant mechanism is the spin-dependent exchange mechanism, not all experimental facts accumulated to date confirm this conclusion. Two experimental approaches that make it possible to reveal the dominant energy-transfer mechanism to Mn2+ ions and evaluate the partial contributions of various mechanisms are considered in the article. One of these approaches is associated with optically detected magnetic resonance at single semimagnetic quantum dots, and the second one is associated with plasmon enhancement of the energy transfer to Mn2+ ions by means of the dipole–dipole interaction.