Low-dimensional Semiconductor Structures Research Articles

Механизмы электронного транспорта в низкоразмерных полупроводниковых структурах: обзор

Background: Low-dimensional semiconductor structures such as quantum wells, wires, and dots have sparked widespread attention due to their distinct electron transport properties that differ dramatically from bulk materials. These characteristics are critical for advances in nanoscale electrical and optoelectronic devices. Objective: The article aims to summarize current knowledge of electron transport processes in low-dimensional semiconductor devices, focusing on the impact of reduced dimensionality on electron behaviour. Methods: A thorough literature analysis was carried out, emphasizing experimental and theoretical investigations that shed light on electron transport dynamics in quantum wells, wires, and dots. The analysis looked into scattering mechanisms, quantum confinement effects, and the significance of material composition and structure. Results: The findings show that quantum confinement produces discrete energy states that drastically change electron mobility and conductivity. Furthermore, electron scattering by phonons, contaminants, and surfaces is shown to be heavily impacted by decreased dimensionality, which either enhances or suppresses electron transport depending on the precise configuration and size of the structures. Conclusion: Low-dimensional semiconductor structures have complex electron transport behaviours that differ significantly from their bulk counterparts. Understanding these mechanisms is critical for designing and developing future electronic devices, and this overview serves as a starting point for ongoing articles on this technologically significant topic.

The influence of light on transverse magnetoresistance oscillations in low-dimensional semiconductor structures

The influence of light on transverse magnetoresistance oscillations in low-dimensional semiconductor structures

Thermodynamic property of one-dimensional hydrogenic impurity in Nitride semiconductor quantum well

ABSTRACT The thermodynamic properties of one-dimensional (1-D) hydrogenic impurity in Nitride semiconductor quantum well have been investigated. Firstly, using a combination of the linear variational approach and the effective mass approximation, we obtain the eigen-energy of hydrogenic impurity states in AlN, GaN and InN quantum wells. Subsequently, we explore the quantum size effect on the thermodynamic properties of these low-dimensional semiconductor structures, revealing some novel and intriguing phenomena. It is found as the width of the quantum well is increased, the energy of hydrogenic impurity gets decreased, however, the thermodynamic parameters, such as the average energy, entropy and heat capacity of the hydrogenic impurity become increased. The physical origins of these peculiar phenomena are attributed to the competitive mechanism between the quantum confinement effect and Coulombic interaction between the electron and impurity. Finally, by conducting a comprehensive comparison of the thermodynamic parameters among GaN, InN, and AlN quantum wells, we propose an innovative strategy for modulating the thermodynamic properties of these low-dimensional semiconductor structures. This manipulation can be achieved not only through external factors such as temperature and quantum well size, but also by altering internal variables like the effective mass and relative dielectric constant of the semiconductor material. This study not only advances our understanding of the thermodynamic properties of hydrogenic impurities in semiconductor quantum wells, but also provides some theoretical guidance for practical applications in fields such as semiconductor physics, condensed matter physics, chemical physics, etc.

Revisiting the adiabatic approximation for bound states calculation in axisymmetric and asymmetrical quantum structures

Abstract The Schrodinger equation in the effective mass approximation is commonly used to calculate the electronic states confined in low-dimensional semiconductor structures. Three-dimensional calculations are unavoidable in the general case of asymmetrical quantum structures and the solutions are not analytical, thus demanding resource-consuming numerical methods. In particular cases, the formalism may be simplified by several approaches: neglecting the gradient of the effective mass, approximating the confinement potentials by simple functions, and exploiting the symmetries in order to reduce the dimensionality of the equation. Particular approaches rarely lead to full analytical solutions, but often to more-convenient, semi-analytical or numerical calculations. We revisit the adiabatic approach for using the Schrodinger formalism in axisymmetric and asymmetrical quantum dots by discussing its reliability as compared with the direct finite element method. We discuss how the difference between the results obtained from the two methods depends on the shape and the symmetry of the quantum structures. We show that adiabatic approach and direct finite element calculation involve similar levels of complexity and computing resources for axisymmetric quantum dots, while providing larger relative differences for flatter structures. On the contrary, for asymmetrical quantum structures, the adiabatic approximation has clearly an advantage regarding the use of computing resources, yet maintaining a high degree of accuracy.

Numerical simulation of a nitride single quantum well laser

Numerical simulation of a quantum well on nitrides, optical interband transitions in low dimensional semiconductor structures (semiconductor quantum wells), conduction-heavy hole and transitions in quantum wells, refinement of the gain for a quantum well on nitride materials with allowance for the overlap integral and approximate this.

Quantitative investigation of intrinsic shear strain and asymmetric interface conditions in semiconductor superlattices

We introduce a convenient and nondestructive method for the quantitative study of symmetry-related factors in low-dimensional semiconductor structures. By experimentally monitoring the intrinsic valence-bands mixing effect (VBME) and its variation with external strain modulation, together with the application of effective-mass theory, intrinsic shear strain and asymmetric interface conditions can be simultaneously determined in InGaAs/InAlAs superlattices. The observed shear strain is of the order of 10−3. Further analysis reveals that the VBME induced by asymmetric interface conditions is weaker than that induced by intrinsic shear strain. In addition, they exhibit a compensating relationship in the studied superlattices. The proposed method can be generalized for quantitative investigation of symmetry-related factors in many other semiconductor nanostructures in the framework of k⋅p perturbation theory.

Copper Doping of Low-Dimensional Se-Based Semiconductor Structures Grown by Molecular Beam Epitaxy

Copper-doped self-assembled CdSe/ZnSe quantum dots (QDs) and (Zn,Cd)Se/ZnSe quantum wells (QWs) are grown by molecular beam epitaxy. Low-temperature luminescence properties of these structures are ...

Multi-Field Coupling Behaviors on Phonon and Thermal/Electrical Properties in Semiconductor Nanostructures

Low-dimensional semiconductor structures such as nanofilms and nanowires have stimulated considerable interest due to their potential applications in nanoelectronic or nanomechanical devices. In this presentation, the effects of pre-stress field and surface stress on the phonon and thermal/electrical properties for semiconductor nanostructures are investigated theoretically. The continuum elastic model is employed to calculate the spatially confined phonon properties. The acoustoelastic effects and surface energy effects are taken into account in calculating the phonon properties of nanostructures. Since the thermal and electric properties are associated with phonon properties of semiconductors, the phonon thermal conductivity, electron-acoustic phonon scattering rate and the carrier mobility are obtained for naonfilms and nanowires under prestress fields and surface stress. The numerical results show that the stress fields have a significant influence on the phonon properties such as the phonon dispersion relation, density of state as well as the group velocity, leading to completely altering the thermal conductivity and the carrier mobility. It is also showed that the appearance of stress can adjust the sensitivity of phonon thermal conductivity and carrier mobility to temperature as well as to the physical size of the nanostructures. These results provide an approach of stress/strain engineering through tuning the phonon properties to control the thermal and electrical properties of nanostructured semiconductors in nanoelectronic devices.

High-Quality In-Plane Aligned CsPbX3 Perovskite Nanowire Lasers with Composition-Dependent Strong Exciton-Photon Coupling.

Cesium lead halide perovskite nanowires have emerged as promising low-dimensional semiconductor structures for integrated photonic applications. Understanding light-matter interactions in a nanowire cavity is of both fundamental and practical interest in designing low-power-consumption nanoscale light sources. In this work, high-quality in-plane aligned halide perovskite CsPbX3 (X = Cl, Br, I) nanowires are synthesized by a vapor growth method on an annealed M-plane sapphire substrate. Large-area nanowire laser arrays have been achieved based on the as-grown aligned CsPbX3 nanowires at room temperature with quite low pumping thresholds, very high quality factors, and a high degree of linear polarization. More importantly, it is found that exciton-polaritons are formed in the nanowires under the excitation of a pulsed laser, indicating a strong exciton-photon coupling in the optical microcavities made of cesium lead halide perovskites. The coupling strength in these CsPbX3 nanowires is dependent on the atomic composition, where the obtained room-temperature Rabi splitting energy is ∼210 ± 13, 146 ± 9, and 103 ± 5 meV for the CsPbCl3, CsPbBr3, and CsPbI3 nanowires, respectively. This work provides fundamental insights for the practical applications of all-inorganic perovskite CsPbX3 nanowires in designing light-emitting devices and integrated nanophotonic systems.

Effects of Strain in Low-Dimensional Semiconductor Structures

Effects of Strain in Low-Dimensional Semiconductor Structures

Resistively Detected Nuclear Magnetic Resonance in Gated Insb QW at Elevated Temperature for Quantum Information Processing

M. M. Uddin,1,2* H. W. Liu,3,4 K. F. Yang,3 T. D. Mishima,5 M. B. Santos,5 K. Nagase,3 and Y. Hirayama1,3,6 1 Department of Physics, Tohoku University, Sendai, Miyagi 980-8578, Japan 2 Department of Physics, Chittagong University of Engineering & Technology, Chittagong-4349, Bangladesh 3 ERATO Nuclear Spin Electronics Project, Sendai, Miyagi 980-8578, Japan 4 State Key Laboratory of Superhard Materials and Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, People’s Republic of China 5 Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks, Norman, Oklahoma 73019-2061, USA 6 WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan *E-mail: mohi_cuet@yahoo.com Narrow band-gap semiconductor InSb has long been considered as potentially exciting materials for next-generation high-speed electronics, quantum devices and spintronics applications due to its high room-temperature mobility (77000 cm2/Vs), significant ballistic transport length, large Lande g factor, high nuclear spin (In=9/2, 121Sb I = 5/2, 123Sb I = 7/2) and high spin-orbit coupling. Nuclear spins in low-dimensional semiconductor structures have attracted growing interest because the long spin coherence time of nuclei facilitates the implementation of quantum information processing (QIP). The quadrupole splitting of 115In have been reported in a single InSb two dimensional electron gas (2DEG) that are of practical importance for the coherent control of the ten nuclear-spin quantum levels and for the implementation of multiple NMR-based quantum bits (≥2) [1, 2]. The success of gate controlled InSb quantum wells [3, 4] allows us to perform pump and probe technique to investigate temperature dependent nuclear spin relaxation time T 1 at different filling factors (ν ). Collective spin excitations in the domain walls enhance dynamic nuclear polarization in the quantum Hall ferromagnet around 2 characterized by a short (~ 60 sec) and temperature-independent T 1. On the other hand, relatively long (~ 400 sec) and temperature dependent T 1with following Korringa law have been demonstrated in the absence of the domains as well as collective spin texture at around 3. In addition, the large Zeeman, cyclotron and exchange energy scales of the InSb 2DEG favour to demonstrate the resistively detected NMR (RDNMR) signal at elevated temperature up to 6 K. Our results clearly show that the InSb 2DEG is a suitable candidate for implementation of the high temperature nuclear-spin based QIP. Ref: [1] H. W. Liu et al. Phys. Rev. B 82, 241304(R) (2010). [2] K. F. Yang et al., Appl. Phys. Lett. 98, 142109 (2011). [3] M. M. Uddin et al., Appl. Phys. Lett. 101, 233503 (2012). [4] M. M. Uddin et al., Appl. Phys. Lett. 103, 123502 (2013). Fig. : Filling factors (ν) dependence of nuclear spin relaxation time T 1 at different temperature. Top axis shows the filling factors are calculated by gate bias (V g) in bottom axis. Figure 1

Polar-surface-driven growth of ZnS microsprings with novel optoelectronic properties

Small perturbations during the growth kinetics of low-dimensional semiconductor structures may lead to novel features, which may provide an ideal system for understanding the fundamental physics of optical phenomena in optoelectronics devices. In this study, we report deformation-free single-crystal zinc sulfide (ZnS) microsprings produced by a polar-surface-driven growth process, and we thoroughly investigate the electrical characteristics of individual ZnS microsprings under electron beam irradiation and their initial applications in ultraviolet (UV) light sensors and waveguides. The microsprings produced are formed by a block-by-block stacking process following a hexagonal screw model that does not introduce distortion into the crystal lattices. The first photodetectors designed based on a single ZnS microspring exhibit a high spectral selectivity combined with a high photosensitivity and a fast response time (<0.3 s) under 320-nm illumination, which make ZnS microsprings particularly valuable as UV-light sensors. Concurrently, excellent waveguide performance along the fiber of a single ZnS microspring (for example, ~0.13 dB μm−1 at 450 nm, and ~0.17 dB μm−1 at 520 nm) is demonstrated for the first time. The high crystal quality, the fast response to UV light and the low propagation loss exhibited by ZnS microsprings indicate that they have important potential applications in nano-optoelectronic systems. High-quality, single-crystal ZnS microsprings have been made and found to have fast responses to ultraviolet light and low propagation loss. The optoelectronic properties of one-dimensional semiconductor structures such as nanowires can be modified by bending them. Now, Tianyou Zhai and colleagues in China have grown deformation-free, single-crystal ZnS microsprings by vapor deposition involving a polar-surface-driven process. They examined the optoelectronic properties of the microsprings and found that irradiation by a high-energy electron beam increases the gain while electron-electron interactions suppress the conductivity. The researchers fabricated photodetectors based on single ZnS microsprings, which exhibited a high photosensitivity and a fast response time to ultraviolet illumination. Furthermore, the microsprings had an excellent waveguide performance. These properties make ZnS microsprings promising for components for future micro/nano-optoelectronic systems. Herein, we reported deformation-free single crystal ZnS microsprings produced by the polar-surface-driven growth process with novel optoelectronic properties for the first time. The entire spring is synthesized by a block-by-block stacking process following a hexagonal screw model, without introducing distortion in crystal lattices. The electrical characteristics of individual ZnS microsprings under electron beam irradiation and their potential applications in UV light sensor and waveguides were thoroughly investigated. The high crystal quality, fast response to UV light and the low propagation loss indicate ZnS microsprings will have important applications in future optoelectronic systems.

High Pressure Semiconductor Physics

D.K. Maude and J.C. Portal, Parallel Transport in Low Dimensional Semiconductor Structures. P.C. Klipstein, Tunneling Under Pressure. E. Anastassakis and M. Cardona, Phonones, Strains, and Pressure in Semiconductors. F.H. Pollak, Effects of External Uniaxial Stress on the Optical Properties of Semiconductors and Semiconductor Microstructures. A.R. Adams, M. Silver, and J. Allam, Semiconductor Optoelectronic Devices. S. Porowski and I. Grzegory, The Application of High N2 Pressure in Physics and Technology of III-N Compounds. M. Yousuf, Diamond Anvils in High Pressure Studies of Semiconductors. Chapter References. Subject Index.

Random lasing of ZnO thin films grown by pulsed-laser deposition

Low-dimensional semiconductor structures on nanometer scale are of great interest because of their strong potential applications in nanotechnologies. We report here optical and structural properties on UV lasing in ZnO thin films. The ZnO films, 110nm thick, were prepared using pulsed-laser deposition on c-cut sapphire substrates at 500°C under 10−2 oxygen pressure. The ZnO films are nearly stoichiometric, dense and display the wurtzite phase. The films are highly textured along the ZnO c-axis and are constituted of nanocrystallites. According to Hall measurements these films are conductive (0.11Ωcm). Photoluminescence measurements reveals a so-called random lasing in the range 390 to 410nm, when illuminating at 355nm with a tripled frequency pulsed Nd-YAG laser. Such random lasing is obtained at rather low optical pumping, 45kWcm−2, a value lower than those classically reported for pulsed-laser deposition thin films.

Interview

Prof. Dieter Bimberg of Technische Universität Berlin in Germany talks about the work behind the Letter ‘Energy-efficient and temperature-stable oxide-confined 980-nm VCSELs operating error-free at 38 Gb/s at 85 °C’ on page 103. Prof. Dieter Bimberg My group's work was originally focussing on the growth and characterisation of low-dimensional semiconductor structures – quantum wells, wires and dots. Mastering growth, I thought more and more about using such structures for devices having properties superior to classical double/multiple heterostructure based ones, being of particular importance for optical communication systems, like Ethernet or Datacom. Important properties are, for example, increased bit rate at large signal operation or high temperature performance. VCSELs are the key enabling devices for optical interconnects in work station clusters and high performance supercomputers. They must simultaneously operate with little energy dissipated, at high bit rate and at high temperature. Generally there is a trade-off between these parameters. We show, for the first time, that high bit rate at high temperatures can be achieved with record energy efficiency. An array of 25 of our VCSELs can transmit a data stream of 1 Tbit/s at an operating temperature of 75°C, typical for the inside of a work station. The internet and its computers at its active end, together with supercomputers, consume an increasing amount of our net electricity production. In 2013 the consumption amounted, in the US, to 5% of production, equalling the photovoltaic power production. For 2014 the prediction is 6% and some predict a brake-even or cross-over in 2023, if the power consumption of the photonic devices is not radically reduced. At the same time the devices must become faster, with larger cut-off frequencies, thus increasing energy consumption. We show here that careful design of the devices significantly reduces the power consumption of VCSELS and allows increased cut-off frequency and resulting maximum bit rate, still at the high temperatures inside a computer. The rapidly increasing number of optical interconnects for short reach (around 300 m and more), very short reach (less than 1 m) and ultra-short reach (less than 1 mm) leads to rapidly increasing consumption of electrical power. We need radical reduction of power consumption to enable further growth of the internet and creation of novel supercomputer generations like Exa-Flop ones, predicted for 2020. Systematic further increase of maximum bit rate of VCSELs and their drivers at the lowest possible energy consumption and still larger operating temperatures. Present theoretical device concepts must be extended to full numerical 3D ones in order to predict the optimum combination of the multitude of parameters which presently influence the performance. Shift of the emission wavelength from 850 nm, 980 nm to longer ones between 1200 and 1300 nm, also enabling p-side down mounting will further increase temperature stability. Device lift-off with redisposition on Si substrates allows us to benefit from the advantageous heat conductivity of Si. The next generation of supercomputers are true optical computers, where optics is decisive and counts for about 50% of the cost and performance. The footprint. We need lasers still much smaller than the present VCSELS in order to deposit arrays of them on memories, logics, microprocessors, where space is limited. Combination of metals with semiconductors will allow shrinking of the feature size of surface emitters by one order of magnitude or more. Plasmonic effects might help. The high speed properties of metal-cavity nanolasers are, however, yet unexplored. In the same way quantum dots as active material might stabilise the active area, reduce losses and improve temperature stability. Putting these features together we can make it happen!

Cylindrical coordinate representation for multiband Hamiltonians

Rotationally invariant combinations of the Brillouin zone-center Bloch functions are used as basis function to express in cylindrical coordinates the valence-band and Kane envelope-function Hamiltonians for wurtzite and zinc-blende semiconductor heterostructures. For cylindrically symmetric systems, this basis allows to treat the envelope functions as eigenstates of the operator of projection of total angular momentum on the symmetry axis, with the operator's eigenvalue conventionally entering the Hamiltonians as a parameter. Complementing the Hamiltonians with boundary conditions for the envelope functions on the symmetry axis, we present for the first time a complete formalism for efficient modeling and description of multiband electron states in low-dimensional semiconductor structures with cylindrical symmetry. To demonstrate the potency of the cylindrical symmetry approximation and establish a criterion of its applicability for actual structures, we map the ground and several excited valence-band states in an isolated wurtzite GaN quantum wire of a hexagonal cross-section to the states in an equivalent quantum wire of a circular cross-section.

Contactless electroreflectance spectroscopy of optical transitions in low dimensional semiconductor structures

AbstractThe authors present the application of contactless electroreflectance (CER) spectroscopy to study optical transitions in low dimensional semiconductor structures including quantum wells (QWs), step-like QWs, quantum dots (QDs), quantum dashes (QDashes), QDs and QDashes embedded in a QW, and QDashes coupled with a QW. For QWs optical transitions between the ground and excited states as well as optical transitions in QW barriers and step-like barriers have been clearly observed in CER spectra. Energies of these transitions have been compared with theoretical calculations and in this way the band structure has been determined for the investigated QWs. For QD and QDash structures optical transitions in QDs and QDashes as well as optical transitions in the wetting layer have been identified. For QDs and QDashes surrounded by a QW, in addition to energies of QD and QDash transitions, energies of optical transitions in the surrounded QW have been measured and the band structure has been determined for the surrounded QW. Finally some differences, which can be observed in CER and photo-reflectance spectra, have been presented and discussed for selected QW and QD structures.

Relating experimental and theoretical perspectives in nanomechanics

To read more about him, turn to page 15. To join TMS, visit www.tms.org/Society/Membership.aspx. With signifi cant advances made in multiscale models and multiscale experiments, a signifi cant gap exists between the two fi elds. Separately, both fi elds have shown a signifi cant promise of discovery. Simulation can provide a cost effective predictability component. On the other hand, experiments can provide a validation and realization component. A signifi cant effort is required to advance a synergistic effort between the two separate fi elds so that a strong unifi ed validation and verifi cation framework that advances discovery and novelty in different scientifi c fi elds can be established. With this point of view, articles in this collection focus on presenting advances made in fi ve different fi elds where efforts focusing on synergistic advancements between simulations and experiments are important. The fi rst article by A.V. Semichaevsky et al. (University of Illinois) focuses on low-dimensional semiconductor (LDS) structures such as quantum dots (QDs), quantum wires, and quantum wells in which electron and hole wave functions are confi ned due to heterogeneous composition and often strongly affected by mismatch strain. An overview of computational and experimental methods for characterization of QD heterostructures is provided. Particularly, focus is on reviewing their concerted efforts to bring together computation and experiment in order to better explain optoelectronic and photovoltaic properties of LDS structures. Creep is non-recoverable high temperature plastic deformation occurring at low load regimes, constant stress valRelating Experimental and Theoretical Perspectives in Nanomechanics

Classical ratchet effects in heterostructures with a lateral periodic potential

We study terahertz radiation induced ratchet currents in low dimensional semiconductor structures with a superimposed one-dimensional lateral periodic potential. The periodic potential is produced by etching a grating into the sample surface or depositing metal stripes periodically on the sample top. Microscopically, the photocurrent generation is based on the combined action of the lateral periodic potential, verified by transport measurements, and the in-plane modulated pumping caused by the lateral superlattice. We show that a substantial part of the total current is caused by the polarization-independent Seebeck ratchet effect. In addition, polarization-dependent photocurrents occur, which we interpret in terms of their underlying microscopical mechanisms. As a result, the class of ratchet systems needs to be extended by linear and circular ratchets, sensitive to linear and circular polarizations of the driving electro-magnetic force.

Transport properties of low-dimensional semiconductor structures in the presence of spin–orbit interaction

Transport properties of a two-dimensional electron gas (2DEG) and of quantum wires are theoretically studied in the presence of both Rashba and Dresselhaus terms of the spin–orbit interaction (SOI). Fully quantum mechanical expressions for the conductivity are evaluated for very low temperatures and the differences between them and previous semiclassical results are highlighted. Two kinds of confining potentials in quantum wires are considered, square-type and parabolic. Various cases depending on the relative strengths of two different SOI terms are discussed and the relaxation times for various impurity potentials are evaluated. In addition, the spin accumulation in a 2DEG and in a quantum wire (QW) is evaluated semiclassically and its dependence on the Fermi energy and the SOI strengths is discussed. A nearly saw-tooth dependence on the electron concentration is obtained for a QW with parabolic confinement.