Editorial

2 pages, 174 KiB

Open AccessEditorial

Semiconductor Quantum Wells and Nanostructures

by Ze Don Kvon

Nanomaterials 2023, 13(13), 1924; https://doi.org/10.3390/nano13131924 - 24 Jun 2023

Cited by 2 | Viewed by 903

Semiconductor quantum wells and nanostructures have been the main quantum and classical physical objects in condensed matter physics for over half a century, since the discovery of the two-dimensional electron gas in silicon MOSFETs and size quantization in thin bismuth films [...] Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

Research

Jump to: Editorial, Review

13 pages, 3258 KiB

Open AccessArticle

An Optical Technique to Produce Embedded Quantum Structures in Semiconductors

by Cyril Hnatovsky, Stephen Mihailov, Michael Hilke, Loren Pfeiffer, Ken West and Sergei Studenikin

Nanomaterials 2023, 13(10), 1622; https://doi.org/10.3390/nano13101622 - 12 May 2023

Cited by 1 | Viewed by 1295

Abstract

The performance of a semiconductor quantum-electronic device ultimately depends on the quality of the semiconductor materials it is made of and on how well the device is isolated from electrostatic fluctuations caused by unavoidable surface charges and other sources of electric noise. Current [...] Read more.

The performance of a semiconductor quantum-electronic device ultimately depends on the quality of the semiconductor materials it is made of and on how well the device is isolated from electrostatic fluctuations caused by unavoidable surface charges and other sources of electric noise. Current technology to fabricate quantum semiconductor devices relies on surface gates which impose strong limitations on the maximum distance from the surface where the confining electrostatic potentials can be engineered. Surface gates also introduce strain fields which cause imperfections in the semiconductor crystal structure. Another way to create confining electrostatic potentials inside semiconductors is by means of light and photosensitive dopants. Light can be structured in the form of perfectly parallel sheets of high and low intensity which can penetrate deep into a semiconductor and, importantly, light does not deteriorate the quality of the semiconductor crystal. In this work, we employ these important properties of structured light to form metastable states of photo-sensitive impurities inside a GaAs/AlGaAs quantum well structure in order to create persistent periodic electrostatic potentials at large predetermined distances from the sample surface. The amplitude of the light-induced potential is controlled by gradually increasing the light fluence at the sample surface and simultaneously measuring the amplitude of Weiss commensurability oscillations in the magnetoresistivity. Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

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19 pages, 1924 KiB

Open AccessArticle

Spin–Orbit and Zeeman Effects on the Electronic Properties of Single Quantum Rings: Applied Magnetic Field and Topological Defects

by José C. León-González, Rafael G. Toscano-Negrette, A. L. Morales, J. A. Vinasco, M. B. Yücel, H. Sari, E. Kasapoglu, S. Sakiroglu, M. E. Mora-Ramos, R. L. Restrepo and C. A. Duque

Nanomaterials 2023, 13(9), 1461; https://doi.org/10.3390/nano13091461 - 25 Apr 2023

Cited by 11 | Viewed by 1580

Abstract

Within the framework of effective mass theory, we investigate the effects of spin–orbit interaction (SOI) and Zeeman splitting on the electronic properties of an electron confined in GaAs single quantum rings. Energies and envelope wavefunctions in the system are determined by solving the [...] Read more.

Within the framework of effective mass theory, we investigate the effects of spin–orbit interaction (SOI) and Zeeman splitting on the electronic properties of an electron confined in GaAs single quantum rings. Energies and envelope wavefunctions in the system are determined by solving the Schrödinger equation via the finite element method. First, we consider an inversely quadratic model potential to describe electron confining profiles in a single quantum ring. The study also analyzes the influence of applied electric and magnetic fields. Solutions for eigenstates are then used to evaluate the linear inter-state light absorption coefficient through the corresponding resonant transition energies and electric dipole matrix moment elements, assuming circular polarization for the incident radiation. Results show that both SOI effects and Zeeman splitting reduce the absorption intensity for the considered transitions compared to the case when these interactions are absent. In addition, the magnitude and position of the resonant peaks have non-monotonic behavior with external magnetic fields. Secondly, we investigate the electronic and optical properties of the electron confined in the quantum ring with a topological defect in the structure; the results show that the crossings in the energy curves as a function of the magnetic field are eliminated, and, therefore, an improvement in transition energies occurs. In addition, the dipole matrix moments present a non-oscillatory behavior compared to the case when a topological defect is not considered. Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

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17 pages, 2720 KiB

Open AccessArticle

A Theoretical Study of Interband Absorption Spectra of Spherical Sector Quantum Dots under the Effect of a Powerful Resonant Laser

by Le Thi Dieu Hien, Le Thi Ngoc Bao, Duong Dinh Phuoc, Hye Jung Kim, C. A. Duque and Dinh Nhu Thao

Nanomaterials 2023, 13(6), 1020; https://doi.org/10.3390/nano13061020 - 11 Mar 2023

Cited by 1 | Viewed by 1645

Abstract

We explore the variation of interband absorption spectra of GaAs spherical sector quantum dots (QDs) in response to a strong resonant laser, using the renormalized wave function method. Even though a spherical sector QD appears identical to a section cut from a spherical [...] Read more.

We explore the variation of interband absorption spectra of GaAs spherical sector quantum dots (QDs) in response to a strong resonant laser, using the renormalized wave function method. Even though a spherical sector QD appears identical to a section cut from a spherical QD, it contains a controllable additional spatial parameter, the apical angle, which results in radically different wave functions and energy levels of particles, and is anticipated to exhibit novel optical properties. The obtained findings reveal that the apical angle of the dot has a considerable effect on the interband absorption spectrum. With the increase in the dot apical angle, a significant redshift of the interband absorption peaks has been identified. Increasing the pump laser detuning and dot radius yields similar results. Especially when a powerful resonant laser with tiny detuning is utilized, a dynamical coupling between electron levels arises, resulting in the formation of new interband absorption peaks. These new peaks and the former ones were similarly influenced by the aforementioned parameters. Furthermore, it is thought that the new peaks, when stimulated by a suitable laser, will produce the entangled states necessary for quantum information. Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

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11 pages, 1950 KiB

Open AccessArticle

Coherence Characteristics of a GaAs Single Heavy-Hole Spin Qubit Using a Modified Single-Shot Latching Readout Technique

by Victor Marton, Andrew Sachrajda, Marek Korkusinski, Alex Bogan and Sergei Studenikin

Nanomaterials 2023, 13(5), 950; https://doi.org/10.3390/nano13050950 - 06 Mar 2023

Cited by 5 | Viewed by 1486

Abstract

We present an experimental study of the coherence properties of a single heavy-hole spin qubit formed in one quantum dot of a gated GaAs/AlGaAs double quantum dot device. We use a modified spin-readout latching technique in which the second quantum dot serves both [...] Read more.

We present an experimental study of the coherence properties of a single heavy-hole spin qubit formed in one quantum dot of a gated GaAs/AlGaAs double quantum dot device. We use a modified spin-readout latching technique in which the second quantum dot serves both as an auxiliary element for a fast spin-dependent readout within a 200 ns time window and as a register for storing the spin-state information. To manipulate the single-spin qubit, we apply sequences of microwave bursts of various amplitudes and durations to make Rabi, Ramsey, Hahn-echo, and CPMG measurements. As a result of the qubit manipulation protocols combined with the latching spin readout, we determine and discuss the achieved qubit coherence times:

T_{1}

,

T_{R a b i}

,

T_{2}^{*}

, and

T_{2}^{C P M G}

vs. microwave excitation amplitude, detuning, and additional relevant parameters. Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

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22 pages, 2096 KiB

Open AccessArticle

Self-Consistent Study of GaAs/AlGaAs Quantum Wells with Modulated Doping

by John A. Gil-Corrales, Alvaro L. Morales and Carlos A. Duque

Nanomaterials 2023, 13(5), 913; https://doi.org/10.3390/nano13050913 - 01 Mar 2023

Cited by 7 | Viewed by 2200

Abstract

In this work, the characterization and analysis of the physics of a GaAs quantum well with AlGaAs barriers were carried out, according to an interior doped layer. An analysis of the probability density, the energy spectrum, and the electronic density was performed using [...] Read more.

In this work, the characterization and analysis of the physics of a GaAs quantum well with AlGaAs barriers were carried out, according to an interior doped layer. An analysis of the probability density, the energy spectrum, and the electronic density was performed using the self-consistent method to solve the Schrödinger, Poisson, and charge-neutrality equations. Based on the characterizations, the system response to geometric changes in the well width and to non-geometric changes, such as the position and with of the doped layer as well as the donor density, were reviewed. All second-order differential equations were solved using the finite difference method. Finally, with the obtained wave functions and energies, the optical absorption coefficient and the electromagnetically induced transparency between the first three confined states were calculated. The results showed the possibility of tuning the optical absorption coefficient and the electromagnetically induced transparency via changes to the system geometry and the doped-layer characteristics. Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

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12 pages, 861 KiB

Open AccessArticle

Harmonic-Gaussian Symmetric and Asymmetric Double Quantum Wells: Magnetic Field Effects

by Esin Kasapoglu, Melike Behiye Yücel and Carlos A. Duque

Nanomaterials 2023, 13(5), 892; https://doi.org/10.3390/nano13050892 - 27 Feb 2023

Cited by 5 | Viewed by 1811

Abstract

In this study, we considered the linear and non-linear optical properties of an electron in both symmetrical and asymmetrical double quantum wells, which consist of the sum of an internal Gaussian barrier and a harmonic potential under an applied magnetic field. Calculations are [...] Read more.

In this study, we considered the linear and non-linear optical properties of an electron in both symmetrical and asymmetrical double quantum wells, which consist of the sum of an internal Gaussian barrier and a harmonic potential under an applied magnetic field. Calculations are in the effective mass and parabolic band approximations. We have used the diagonalization method to find eigenvalues and eigenfunctions of the electron confined within the symmetric and asymmetric double well formed by the sum of a parabolic and Gaussian potential. A two-level approach is used in the density matrix expansion to calculate the linear and third-order non-linear optical absorption and refractive index coefficients. The potential model proposed in this study is useful for simulating and manipulating the optical and electronic properties of symmetric and asymmetric double quantum heterostructures, such as double quantum wells and double quantum dots, with controllable coupling and subjected to externally applied magnetic fields. Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

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18 pages, 1711 KiB

Open AccessArticle

Optical Properties in a ZnS/CdS/ZnS Core/Shell/Shell Spherical Quantum Dot: Electric and Magnetic Field and Donor Impurity Effects

by Rafael G. Toscano-Negrette, José C. León-González, Juan A. Vinasco, A. L. Morales, Fatih Koc, Ahmet Emre Kavruk, Mehmet Sahin, M. E. Mora-Ramos, José Sierra-Ortega, J. C. Martínez-Orozco, R. L. Restrepo and C. A. Duque

Nanomaterials 2023, 13(3), 550; https://doi.org/10.3390/nano13030550 - 29 Jan 2023

Cited by 12 | Viewed by 2244

Abstract

A theoretical analysis of optical properties in a ZnS/CdS/ZnS core/shell/shell spherical quantum dot was carried out within the effective mass approximation. The corresponding Schrödinger equation was solved using the finite element method via the 2D axis-symmetric module of COMSOL-Multiphysics software. Calculations included variations [...] Read more.

A theoretical analysis of optical properties in a ZnS/CdS/ZnS core/shell/shell spherical quantum dot was carried out within the effective mass approximation. The corresponding Schrödinger equation was solved using the finite element method via the 2D axis-symmetric module of COMSOL-Multiphysics software. Calculations included variations of internal dot radius, the application of electric and magnetic fields (both oriented along z-direction), as well as the presence of on-center donor impurity. Reported optical properties are the absorption and relative refractive index change coefficients. These quantities are related to transitions between the ground and first excited states, with linearly polarized incident radiation along the z-axis. It is found that transition energy decreases with the growth of internal radius, thus causing the red-shift of resonant peaks. The same happens when the external magnetic field increases. When the strength of applied electric field is increased, the opposite effect is observed, since there is a blue-shift of resonances. However, dipole matrix moments decrease drastically with the increase of the electric field, leading to a reduction in amplitude of optical responses. At the moment impurity effects are activated, a decrease in the value of the energies is noted, significantly affecting the ground state, which is more evident for small internal radius. This is reflected in an increase in transition energies. Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

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12 pages, 4050 KiB

Open AccessFeature PaperArticle

Vacuum Spin LED: First Step towards Vacuum Semiconductor Spintronics

by Oleg E. Tereshchenko, Vladimir A. Golyashov, Vadim S. Rusetsky, Danil A. Kustov, Andrey V. Mironov and Alexander Yu. Demin

Nanomaterials 2023, 13(3), 422; https://doi.org/10.3390/nano13030422 - 19 Jan 2023

Cited by 3 | Viewed by 1490

Abstract

Improving the efficiency of spin generation, injection, and detection remains a key challenge for semiconductor spintronics. Electrical injection and optical orientation are two methods of creating spin polarization in semiconductors, which traditionally require specially tailored p-n junctions, tunnel or Schottky barriers. Alternatively, we [...] Read more.

Improving the efficiency of spin generation, injection, and detection remains a key challenge for semiconductor spintronics. Electrical injection and optical orientation are two methods of creating spin polarization in semiconductors, which traditionally require specially tailored p-n junctions, tunnel or Schottky barriers. Alternatively, we introduce here a novel concept for spin-polarized electron emission/injection combining the optocoupler principle based on vacuum spin-polarized light-emitting diode (spin VLED) making it possible to measure the free electron beam polarization injected into the III-V heterostructure with quantum wells (QWs) based on the detection of polarized cathodoluminescence (CL). To study the spin-dependent emission/injection, we developed spin VLEDs, which consist of a compact proximity-focused vacuum tube with a spin-polarized electron source (p-GaAs(Cs,O) or Na₂KSb) and the spin detector (III-V heterostructure), both activated to a negative electron affinity (NEA) state. The coupling between the photon helicity and the spin angular momentum of the electrons in the photoemission and injection/detection processes is realized without using either magnetic material or a magnetic field. Spin-current detection efficiency in spin VLED is found to be 27% at room temperature. The created vacuum spin LED paves the way for optical generation and spin manipulation in the developing vacuum semiconductor spintronics. Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

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10 pages, 781 KiB

Open AccessFeature PaperArticle

Interface Superconductivity in a Dirac Semimetal NiTe₂

by Varnava D. Esin, Oleg O. Shvetsov, Anna V. Timonina, Nikolai N. Kolesnikov and Eduard V. Deviatov

Nanomaterials 2022, 12(23), 4114; https://doi.org/10.3390/nano12234114 - 22 Nov 2022

Cited by 5 | Viewed by 1896

Abstract

We experimentally investigated charge transport through a single planar junction between a NiTe

_{2}

Dirac semimetal and a normal gold lead. At milli-Kelvin temperatures, we observe non-Ohmic

d V / d I (V)

behavior resembling Andreev reflection at a superconductor–normal metal [...] Read more.

We experimentally investigated charge transport through a single planar junction between a NiTe

_{2}

Dirac semimetal and a normal gold lead. At milli-Kelvin temperatures, we observe non-Ohmic

d V / d I (V)

behavior resembling Andreev reflection at a superconductor–normal metal interface, while NiTe

_{2}

bulk remains non-superconducting. The conclusion on superconductivity is also supported by the suppression of the effect by temperature and magnetic field. In analogy with the known results for Cd

_{3}

As

_{2}

Dirac semimetal, we connect this behavior with interfacial superconductivity due to the flat-band formation at the Au-NiTe

_{2}

interface. Since the flat-band and topological surface states are closely connected, the claim on the flat-band-induced superconductivity is also supported by the Josephson current through the topological surface states on the pristine NiTe

_{2}

surface. We demonstrate the pronounced Josephson diode effect, which results from the momentum shift of the topological surface states of NiTe

_{2}

under an in-plane magnetic field. Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

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15 pages, 47799 KiB

Open AccessArticle

β-Ga₂O₃ Nanostructures: Chemical Vapor Deposition Growth Using Thermally Dewetted Au Nanoparticles as Catalyst and Characterization

by Asha Yadav, Bo Fu, Stephanie Nicole Bonvicini, Linh Quy Ly, Zhitai Jia and Yujun Shi

Nanomaterials 2022, 12(15), 2589; https://doi.org/10.3390/nano12152589 - 28 Jul 2022

Cited by 5 | Viewed by 1829

Abstract

β-Ga₂O₃ nanostructures, including nanowires (NWs), nanosheets (NSHs), and nanorods (NRs), were synthesized using thermally dewetted Au nanoparticles as catalyst in a chemical vapor deposition process. The morphology of the as-grown β-Ga₂O₃ nanostructures depends strongly on [...] Read more.

β-Ga₂O₃ nanostructures, including nanowires (NWs), nanosheets (NSHs), and nanorods (NRs), were synthesized using thermally dewetted Au nanoparticles as catalyst in a chemical vapor deposition process. The morphology of the as-grown β-Ga₂O₃ nanostructures depends strongly on the growth temperature and time. Successful growth of β-Ga₂O₃ NWs with lengths of 7–25 μm, NSHs, and NRs was achieved. It has been demonstrated that the vapor–liquid–solid mechanism governs the NW growth, and the vapor–solid mechanism occurs in the growth of NSHs and NRs. The X-ray diffraction analysis showed that the as-grown nanostructures were highly pure single-phase β-Ga₂O₃. The bandgap of the β-Ga₂O₃ nanostructures was determined to lie in the range of 4.68–4.74 eV. Characteristic Raman peaks were observed with a small blue and red shift, both of 1–3 cm⁻¹, as compared with those from the bulk, indicating the presence of internal strain and defects in the as-grown β-Ga₂O₃ nanostructures. Strong photoluminescence emission in the UV-blue spectral region was obtained in the β-Ga₂O₃ nanostructures, regardless of their morphology. The UV (374–377 nm) emission is due to the intrinsic radiative recombination of self-trapped excitons present at the band edge. The strong blue (404–490 nm) emissions, consisting of five bands, are attributed to the presence of the complex defect states in the donor (V_O) and acceptor (V_Ga or V_Ga–O). These β-Ga₂O₃ nanostructures are expected to have potential applications in optoelectronic devices such as tunable UV–Vis photodetectors. Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

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10 pages, 454 KiB

Open AccessArticle

Band Structure Near the Dirac Point in HgTe Quantum Wells with Critical Thickness

by Alexey Shuvaev, Vlad Dziom, Jan Gospodarič, Elena G. Novik, Alena A. Dobretsova, Nikolay N. Mikhailov, Ze Don Kvon and Andrei Pimenov

Nanomaterials 2022, 12(14), 2492; https://doi.org/10.3390/nano12142492 - 20 Jul 2022

Cited by 3 | Viewed by 1419

Abstract

Mercury telluride (HgTe) thin films with a critical thickness of 6.5 nm are predicted to possess a gapless Dirac-like band structure. We report a comprehensive study on gated and optically doped samples by magnetooptical spectroscopy in the THz range. The quasi-classical analysis of [...] Read more.

Mercury telluride (HgTe) thin films with a critical thickness of 6.5 nm are predicted to possess a gapless Dirac-like band structure. We report a comprehensive study on gated and optically doped samples by magnetooptical spectroscopy in the THz range. The quasi-classical analysis of the cyclotron resonance allowed the mapping of the band dispersion of Dirac charge carriers in a broad range of electron and hole doping. A smooth transition through the charge neutrality point between Dirac holes and electrons was observed. An additional peak coming from a second type of holes with an almost density-independent mass of around

0.04 m_{0}

was detected in the hole-doping range and attributed to an asymmetric spin splitting of the Dirac cone. Spectroscopic evidence for disorder-induced band energy fluctuations could not be detected in present cyclotron resonance experiments. Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

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9 pages, 1615 KiB

Open AccessFeature PaperArticle

Quantum Transport of Dirac Fermions in HgTe Gapless Quantum Wells

by Gennady M. Gusev, Alexander D. Levin, Dmitry A. Kozlov, Ze D. Kvon and Nikolay N. Mikhailov

Nanomaterials 2022, 12(12), 2047; https://doi.org/10.3390/nano12122047 - 14 Jun 2022

Cited by 2 | Viewed by 1467

Abstract

We study the transport properties of HgTe quantum wells with critical well thickness, where the band gap is closed and the low energy spectrum is described by a single Dirac cone. In this work, we examined both macroscopic and micron-sized (mesoscopic) samples. In [...] Read more.

We study the transport properties of HgTe quantum wells with critical well thickness, where the band gap is closed and the low energy spectrum is described by a single Dirac cone. In this work, we examined both macroscopic and micron-sized (mesoscopic) samples. In micron-sized samples, we observe a magnetic-field-induced quantized resistance (~h/2e) at Landau filling factor

ν = 0

, corresponding to the formation of helical edge states centered at the charge neutrality point (CNP). In macroscopic samples, the resistance near a zero Landau level (LL) reveals strong oscillations, which we attribute to scattering between the edge

ν = 0

state and bulk

ν \neq 0

hole LL. We provide a model taking an empirical approach to construct a LL diagram based on a reservoir scenario, formed by the heavy holes. Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

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Review

Jump to: Editorial, Research

16 pages, 552 KiB

Open AccessReview

Two-Dimensional Plasmons in Laterally Confined 2D Electron Systems

by Igor V. Zagorodnev, Andrey A. Zabolotnykh, Danil A. Rodionov and Vladimir A. Volkov

Nanomaterials 2023, 13(6), 975; https://doi.org/10.3390/nano13060975 - 08 Mar 2023

Cited by 2 | Viewed by 1523

Abstract

The collective oscillations of charge density (plasmons) in conductive solids are basic excitations that determine the dynamic response of the system. In infinite two-dimensional (2D) electron systems, plasmons have gapless dispersion covering a broad spectral range from subterahertz to infrared, which is promising [...] Read more.

The collective oscillations of charge density (plasmons) in conductive solids are basic excitations that determine the dynamic response of the system. In infinite two-dimensional (2D) electron systems, plasmons have gapless dispersion covering a broad spectral range from subterahertz to infrared, which is promising in light-matter applications. We discuss the state-of-the-art physics of 2D plasmons, especially in confined 2D electron systems in stripe and disk geometry, using the simplest approach for conductivity. When the metal gate is placed in the vicinity of the 2D electron system, an analytical description of the plasmon frequency and damping can be easily obtained. We also analyze gated plasmons in the disk when it was situated at various distances from the gate, and discuss in detail the nontrivial behavior of the damping. We predict that it is not a simple sum of the radiative and collisional dampings, but has a nonmonotonic dependence on the system parameters. For high-mobility 2D systems, this opens the way to achieve the maximal quality factor of plasma resonances. Lastly, we discuss the recently discovered near-gate 2D plasmons propagating along the laterally confined gate, even without applied bias voltage and having gapless dispersion when the gate has the form of a stripe, and discrete spectrum when the gate is in the form of disk. It allows for one to drive the frequency and spatial propagation of such plasmons. Full article

(This article belongs to the Special Issue Semiconductor Quantum Wells and Nanostructures)

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