Electronic Band Profiles Research Articles

HADOKEN: An open-source software package for predicting electron confinement effects in various nanowire geometries and configurations

We present an open-source software package, HADOKEN (High-level Algorithms to Design, Optimize, and Keep Electrons in Nanowires), for predicting electron confinement/localization effects in nanowires with various geometries, arbitrary number of concentric shell layers, doping densities, and external boundary conditions. The HADOKEN code is written in the MATLAB programming environment to aid in its readability and general accessibility to both users and practitioners. We provide several examples and outputs on a variety of different nanowire geometries, boundary conditions, and doping densities to demonstrate the capabilities of the HADOKEN software package. As such, the use of this predictive and versatile tool by both experimentalists and theorists could lead to further advances in both understanding and tailoring electron confinement effects in these nanosystems. Program summaryProgram Title: HADOKENCPC Library link to program files:https://doi.org/10.17632/jyzk4gfytx.1Licensing provisions: GNU General Public License 3Programming language: MATLABNature of problem: HADOKEN utilizes iterative finite element methods to solve coupled Schrödinger and Poisson equations for heterostructure core–shell nanowires with arbitrary cross-sectional geometries. The user-friendly program outputs graphical results of electronic energies, densities, wavefunctions, and band profiles for various user-supplied input parameters.Solution method: iterative solution of coupled Schrödinger and Poisson equations using finite element methods and sparse matrix linear algebra.

Control of electronic band profiles through depletion layer engineering in core\u2013shell nanocrystals

Fermi level pinning in doped metal oxide (MO) nanocrystals (NCs) results in the formation of depletion layers, which affect their optical and electronic properties, and ultimately their application in smart optoelectronics, photocatalysis, or energy storage. For a precise control over functionality, it is important to understand and control their electronic bands at the nanoscale. Here, we show that depletion layer engineering allows designing the energetic band profiles and predicting the optoelectronic properties of MO NCs. This is achieved by shell thickness tuning of core–shell Sn:In2O3–In2O3 NCs, resulting in multiple band bending and multi-modal plasmonic response. We identify the modification of the band profiles after the light-induced accumulation of extra electrons as the main mechanism of photodoping and enhance the charge storage capability up to hundreds of electrons per NC through depletion layer engineering. Our experimental results are supported by theoretical models and are transferable to other core-multishell systems as well.

Electronic band profiles, magnetic stability, antiferromagnetic spins ordering and thermodynamics properties of novel antiferromagnet CaCr2Sb2

We have analyzed the magnetic stability; antiferromagnetic spin ordering; electronic, magnetic and thermodynamic properties of CaCr2 Sb2 compound using the framework of density functional theory (DFT) with full-potential augmented-plane wave (FP-APW) method within the generalized gradient (PBE-GGA, Tran-Blaha modifies GGA) plus Hubbard potential U (GGA + U ) functional as exchange correlation potentials. We have clearly specified that the antiferromagnetic state is most favorable for CaCr2 Sb2 as compared to other configurations at their structural relaxed lattice parameters. In antiferromagnetic (AFM ) spin configuration, a Cr atom is shown to be in an impressive state of CaCr2 Sb2 compound. Based on its band structures and density of state (DOS), CaCr2 Sb2 has a metallic character in paramagnetic (PM ) and antiferromagnetic phase (AFM ). From projected densities of states, it is considered that the primarily bonding is achieved throughout hybridization of Cr (3d) with Sb (p ) states. Moreover, pressure and temperature contingent thermodynamic parameters are calculated in the range of 0 to 1000 K and 0 to 18 GPa for temperature and pressure, respectively, with a step range of 3 GPa, respectively. The total magnetic moment of CaCr2 Sb2 is confirmed to be 0.00008/4.07 μ B in the antiferromagnetic/ferromagnetic configuration respectively using GGA + U where its major contribution originates from Cr atoms.

First‐principles study on structural, electronic, magnetic, elastic, mechanical and thermodynamic properties of Mn 2 PtCo Heusler alloy

The structural, electronic, magnetic, mechanical and thermodynamic properties of the Mn2PtCo Heusler alloy have been investigated in the frame work of density functional theory (DFT). The cohesive energies confirm the Cu2MnAl-prototype structure of Mn2PtCo with the ferromagnetic phase. The spin polarized electronic band profile of the Mn2PtCo exhibits its metallic character by considering the generalized gradient approximation (GGA) and modified Becke-Johnson (GGA-mBJ) approximation in the calculations. The magnetic moment is calculated to ~9 μB and it is in accordance with the Slater-Pauling rule. From the analysis of mechanical properties the brittle nature is anticipated. Further to seek the applications of Mn2PtCo in device fabrication, the thermodynamic properties like entropy, heat capacity at constant volume, Debye temperature, Gruneisen parameter and thermal expansion coefficient within the temperature and pressure range of 0 to 1000 K and 0 to 24 GPa, respectively have also been estimated.

Insights into the structural, electronic and optical properties of MgA2B4(A = Sc, Y; B = S, Se) spinel compounds: Direct energy band gap materials

Direct bandgap bulk materials are very important for the optical applications. It is therefore important to predict new materials with the desired properties. In the present work, density functional theory is applied to study different physical properties of MgA2B4 (A = Sc, Y; B= S, Se) spinel compounds. Generalized gradient approximation is used to study the structural and elastic parameters while modified Becke Johnson exchange potential is applied to calculate electronic band profiles and optical properties. The studied compounds are stable in cubic structure. Also, energy bandgaps of the compounds are of direct nature. Therefore, these compounds can find useful applications in the optoelectronics devices. Optical properties of these compounds are studied in terms of dielectric function, refractive index, extinction coefficient, optical conductivity and reflectivity. The transport parameters like electrical conductivity and thermal conductivity are also evaluated.

Tunneling mechanism in a (Ga,Mn)As/GaAs-based spin Esaki diode investigated by bias-dependent shot noise measurements

Electron transport across a tunneling barrier is governed by intricate and diverse causes such as interface conditions, material properties, and device geometries. Here, by measuring the shot noise, we investigate electron transport in a (Ga,Mn)As/GaAs-based spin Esaki diode junction over a wide range of bias voltage. The asymmetric electronic band profile across the junction allows us to tune the types of tunneling process. By changing the bias voltage in a single device, we successively address the conventional direct tunneling, the excess current conduction through the mid-gap localized states, and the thermal excitation current conduction. These observations lead to a proper comparison of the bias dependent Fano factors. While the Fano factor is unity for the direct tunneling, it is pronouncedly reduced in the excess current region. Thus, we have succeeded in evaluating several types of conduction process with the Fano factor in a single junction.

Anion replacement effect on BaCd2X2 (X = P, As, Sb, Bi) compounds: A first principles study

Cadmium based Zintl phase compounds have been recently studied for the thermoelectric applications. Many interesting experimental results reported on the 1-2-2 cadmium based compounds, however less attention been paid to study them though first principles methods. In the current work, BaCd2X2 (X= P, As, As, Bi) compounds have been studied comprehensively for the basic structural parameters, electronic band profiles, optical characteristics and thermoelectric properties. Poirier–Tarantola equation of state is used to fit the volume and energy data. The calculated results are consistent with the reported experimental results. Electronic band profiles of the compounds reveal that the compounds are semiconductors except BaCd2Bi2 which is metallic. Valence band is composed on mainly X-p states while Ba-d state in conduction band. Compounds show prominent absorption in the visible region with extension to low frequency ultraviolet region. The characteristics optical peaks redshifted by anion replacement from P to Bi. Thermoelectric properties of the compounds are also studied for possible thermoelectric applications.

Study of anion replacement effect on SrCd2X2 (X = P, As, Sb, Bi) compounds by FPLAPW+lo

The structural parameters, optoelectronic and thermoelectric properties of SrCd2X2 (X = P, As, Sb and Bi) compounds have been investigated thoroughly for the first time using first principles methods. The compounds are optimized and obtained structural parameters agree to the experimental data. Electronic band profiles of the compounds reveal that the SrCd2P2, SrCd2As2, SrCd2Sb are direct band gap semiconductors while SrCd2Bi2 is metallic. Valence band is composed on mainly X-p states while Sr-d state in conduction band. Compounds show the strong absorption in the visible region and low frequency ultraviolet region. The characteristics optical peaks shift towards lower energy by replacing the anion from P to Bi. Boltzmann transport theory is implemented through the BoltzTraP code to calculate the electrical and thermal conductivities, Seebeck coefficients and thermo power factor. High absorption peaks and figure of merits of the compounds show that these compounds can be important for optoelectronics and thermo-electric devices.

Electronic band profiles and magneto-electronic properties of ternary XCu2P2 (X = Ca, Sr) compounds: insight from ab initio calculations

Abstract Full-potential augmented plane waves (FP-APW) method is applied to determine the electronic band profiles and magneto-electronic properties of XCu2P2 (X = Ca, Sr) compounds. We have adopted Perdew, Burke and Ernzerhof's generalized gradient approximation (PBE-GGA) along with GGA plus Hubbard U parameter method (GGA+U) as exchange correlation potentials. The physical properties of interest for XCu2P2 (X = Ca, Sr) compounds were analyzed for the first time in the Zintl phase of tetragonal structure with space group I4/mmm (No. 139). From the structural parameters we have found that ferromagnetic phase is more stable as compared to paramagnetic and antiferromagnetic phase. Electronic band profiles predict the metallic nature of these compounds in FM phase. The projected densities of states computed in this work recognize that the bonding is accomplished through hybridization of Cu-3d with P-p states. The evaluated magnetic moments support weak ferromagnetism in these compounds. The compounds of interest are thermodynamically stable. In addition, the cohesive energies and Curie temperatures of the studied compounds were also predicted. Metallic and ferromagnetic nature of XCu2P2 (X = Ca, Sr) compounds predict the important of these compounds in spintronic devices.

Investigations of structural, elastic, electronic, vibrational and thermodynamic properties of RhMnX (X = Sb and Sn)

This study employs first principles method to run an investigation on structural, electronic, elastic, vibrational, thermodynamic and magnetic properties of RhMnX (X = Sb and Sn) half-Heusler compounds in C1b phase. The elastic constants (C11, C12 and C44) for RhMnX (X = Sb and Sn) half-Heusler compounds in C1b phase are computed using the energy-strain method. Directional changes of Young and Shear modulus, Poisson’s ratios and compressibility’s of RhMnX (X = Sb and Sn) compounds have been analysed. Evaluations of mechanical stabilities via obtained elastic constants are exhibited stable natures for these compounds. Moreover, the compounds are ductile based on the Pugh’s criteria. Electronic band structures and their partial density of states are presented for both compounds and used to interpret the electronic band profiles of these compounds in the C1b phase. Specifically, phonon dispersion curves of these compounds have been derived for the first time. Full phonon properties of these compounds suggest that both compounds are dynamically stable. Besides, the change in specific heat capacity and entropy of RhMnX (X = Sb and Sn) compounds have been also computed between 0–500 K.

Exploration of highly correlated Co‐based quaternary Heusler alloys for spintronics and thermoelectric applications

The half-metallic character of new quaternary Heusler alloys CoXMnAs (X = Ru, Rh) is established along with their thermoelectric, mechanical, and thermodynamic properties. The optimization of energy suggests that alloys are stable in Y2-type structure with a ferromagnetic character. The electronic band profile through generalized gradient approximation and modified Becke-Johnson potential indicates the metallic character of alloys. However, with inclusion of Hubbard potential to generalized gradient approximation, the alloys depict half-metallic character with semiconducting nature in spin-down state. The alloys possess high magnetic moment, CoRuMnAs has 5 μB, whereas CoRhMnAs has 6 μB, following Slater-Pauling rule MT = ZT − 24. The narrow band gap in spin-down channel enhances the thermoelectric properties. The maximum value for thermopower (|S|) obtained is 44.3 and 53.44 μV/K for CoRuMnAs and CoRhMnAs, respectively. The variation of electrical conductivity, Seebeck coefficient, and figure of merit affirm increasing trend with temperature, which is a good indication of materials to be used in thermoelectric technology. The mechanical stability along with ductile nature of alloys is determined through elastic constants. Further, we have calculated thermodynamic properties and have established their dependence on temperature and pressure using quasi-harmonic Debye model. The half-metallic nature with efficient thermoelectric parameters strongly supports the possible application of alloys for spin devices and green energy generation.

Backgrounds and pulse shape discrimination in the ArDM liquid argon TPC

The ArDM experiment completed a single-phase commissioning run (ArDM Run I) with an active liquid argon target of nearly one tonne in mass. The analysis of the data and comparison to predictions from full detector simulations allowed extraction of the detector properties and an assessment of the low background conditions. The 39Ar specific activity from the employed atmospheric argon is measured to be (0.95±0.05) Bq/kg. The cosmic muon flux at the Canfranc underground site was determined to be in the range (2–3.5)× 10−3m−2s−1. The statistical rejection power for electronic recoil events using the pulse shape discrimination method was estimated using a 252Cf neutron calibration source. Electronic and nuclear recoil band profiles were found to be well described by Gaussian distributions. Employing such a model we derive values for the electronic recoil statistical rejection power of more than 108 in the tonne-scale liquid argon target for events with more than 50 detected photons at a 50% acceptance for nuclear recoils. The 222Rn emanation rate of the ArDM cryostat at room temperature was found to be (65.6±0.4) μHz/l. These results represent an important physics milestone for the next run in the double-phase mode and in the context of foreseen developments towards the use of depleted argon targets.

Analytical modeling of temperature and power dependent photoluminescence (PL) spectra of InAs/GaAs quantum dots

In order to theoretically analyze the Photoluminescence (PL) spectra and its dependence on temperature and power, we have calculated the electronic band structure of self-assembled InAs/GaAs Quantum Dots (QDs) with a temperature dependent 8 band k·p Hamiltonian by including the effects of strain. The transition energies for the ground state and the first excited state are calculated using a mathematical model, which takes into account the effect of both homogeneous and inhomogeneous broadening, caused due to carrier scattering processes and QD size variation, respectively. Our proposed analytical model describes the origin of bimodal peak in the PL spectra and its correlation with the transition energies for different temperatures by considering the temperature induced intrinsic carrier concentration and carrier relaxation time. The applicability of the derived expression is validated using the experimental data of single layer InAs/GaAs QDs grown using Stranski-Krastanov growth mode. In addition to this, the simplicity of the model and its various useful aspects including computation of temperature dependent electronic band profiles and complete PL spectra make it a potential tool to study the optoelectronic properties of QD heterostructures.

Electronic band profiles and optical response of Cd3Y2 (Y= N, P and As) compounds

Cubic and tetragonal phases of Cd3Y2 (Y= N, P and As) compounds are studied using full potential approach of density functional theory. All the studied crystal structures were fully optimized using the generalized gradient approximation. Calculated structural parameters agree well with experimental measurements. Electronic band profiles reveal metallic nature of Cd3Y2 in both phases except Cd3P2 which is semiconductor with small band gap value. The charge sharing is dominant in cubic and tetragonal phases which show covalent bond nature. Optical properties of the compounds are studied in detail in both phases. Interestingly, it is revealed that the intraband transitions play vital rule in explaining the optical properties in the metals while no influence observed in the Dirac semi-metal and semiconducting nature in these compounds. The reflectivity of metallic behavior compounds Cd3P2 and Cd3As2 reached up to 90% with the intra band calculation.

Interfacial Coupling Effect on Electron Transport in MoS2/SrTiO3 Heterostructure: An Ab-initio Study

A variety of theoretical and experimental works have reported several potential applications of MoS2 monolayer based heterostructures (HSs) such as light emitting diodes, photodetectors and field effect transistors etc. In the present work, we have theoretically performed as a model case study, MoS2 monolayer deposited over insulating SrTiO3 (001) to study the band alignment at TiO2 termination. The interfacial characteristics are found to be highly dependent on the interface termination. With an insulating oxide material, a significant band gap (0.85eV) is found in MoS2/TiO2 interface heterostructure (HS). A unique electronic band profile with an indirect band gap (0.67eV) is observed in MoS2 monolayer when confined in a cubic environment of SrTiO3 (STO). Adsorption analysis showed the chemisorption of MoS2 on the surface of STO substrate with TiO2 termination which is justified by the charge density calculations that shows the existence of covalent bonding at the interface. The fabrication of HS of such materials paves the path for developing the unprecedented 2D materials with exciting properties such as semiconducting devices, thermoelectric and optoelectronic applications.

Flexible Modulation of Electronic Band Structures of Wide Band Gap GaN Semiconductors Using Bioinspired, Nonbiological Helical Peptides

AbstractModulation of the electronic band profiles of wide band gap GaN semiconductors is achieved by the macromolecular dipole potentials exerted from ordered monolayers of synthetic, nonbiological aldehyde terminated helical peptides deposited on wet chemically oxidized GaN surfaces functionalized with aminosilanes. The selective coupling of either N‐ or C‐terminal to the amino‐terminated surface enables one to control the direction of the dipole moment, while the number of amino acids determines its magnitude. After confirming the formation of highly ordered peptide monolayers, the impact of macromolecular dipole potentials is quantified by electrochemical impedance spectroscopy. Moreover, the chronoamperometry measurements of ferrocene‐terminated peptides suggest that the transfer of electrons injected from ferrocene follows inelastic hopping, while the current responses of peptides with no ferrocene moieties are purely capacitive. Finally, the same functionalization steps are transferred to GaN/AlGaN/GaN high electron mobility transistor structures. Stable and quantitative modulation of the current–voltage characteristics of the 2D electron gas by the deposition of bioinspired peptides is a promising strategy for the macromolecular dipole engineering of GaN semiconductors.

Insulating-to-conducting behavior and band profile across the La0.9Ba0.1MnO3/Nb:SrTiO3 epitaxial interface

$\mathrm{L}{\mathrm{a}}_{0.9}\mathrm{B}{\mathrm{a}}_{0.1}\mathrm{Mn}{\mathrm{O}}_{3}$ is a ferromagnetic insulator in its bulk form, but exhibits metallicity in thin-film form. It has a wide potential in a range of spintronic-related applications, and hence it is critical to understand thickness-dependent electronic structure in thin films as well as substrate/film interface effects. Here, using electrical and in situ photoemission spectroscopy measurements, we report the electronic structure and interface band profile of high-quality layer-by-layer-grown $\mathrm{L}{\mathrm{a}}_{0.9}\mathrm{B}{\mathrm{a}}_{0.1}\mathrm{Mn}{\mathrm{O}}_{3}$ on single-crystal $\mathrm{Nb}:\mathrm{SrTi}{\mathrm{O}}_{3}$ substrates. A transition from insulating-to-conducting was observed with increasing $\mathrm{L}{\mathrm{a}}_{0.9}\mathrm{B}{\mathrm{a}}_{0.1}\mathrm{Mn}{\mathrm{O}}_{3}$ thickness, which was explained by the determined interface band diagram of $\mathrm{L}{\mathrm{a}}_{0.9}\mathrm{B}{\mathrm{a}}_{0.1}\mathrm{Mn}{\mathrm{O}}_{3}$/$\mathrm{Nb}:\mathrm{SrTi}{\mathrm{O}}_{3}$, where a type II heterojunction was formed.

Engineering ferroelectric tunnel junctions through potential profile shaping

We explore the influence of the top electrode materials (W, Co, Ni, Ir) on the electronic band profile in ferroelectric tunnel junctions based on super-tetragonal BiFeO3. Large variations of the transport properties are observed at room temperature. In particular, the analysis of current vs. voltage curves by a direct tunneling model indicates that the metal/ferroelectric interfacial barrier height increases with the top-electrode work function. While larger metal work functions result in larger OFF/ON ratios, they also produce a large internal electric field which results in large and potentially destructive switching voltages.

Structural and magnetic properties of TlTF3 (T=Fe, Co and Ni) by hybrid functional theory

DFT studies are performed to investigate the structural, mechanical and magneto-electronic properties of the TlTF3 (T=Fe, Co and Ni) perovskites for the first time using GGA, GGA+U and hybrid density functional theory (HF). Our calculations show that HF give better results than GGA and GGA+U and more consistent with the experiments. The comparison of the lattice constants calculated by HF with experiments shows a maximum underestimation less than 0.2%. The chemical bonding between different ions in these compounds is explained on the bases of electronic clouds, which reveals that in TlFeF3, Fe has more ionic character with F than the rest. The mechanical properties explain the hardness of these compounds and show that TlFeF3 is more ductile. Spin-dependent electronic band profiles show that TlFeF3 and TlCoF3 are metallic, whereas TlNiF3 is pseudo direct wide bandgap semiconductor. The stable magnetic phase optimizations and the calculated magnetic susceptibility confirm that TlFeF3 and TlNiF3 are ferromagnetic whereas TlCoF3 is anti-ferromagnetic material.

Magneto-electronic studies of the inverse-perovskite (Eu3O)In

Abstract Ferromagnetic metallic inverse-perovskite (Eu3O)In is studied using hybrid functional theory (HF) in the frame work DFT. The calculated structural parameters and geometries of the material are calculated by different exchange correlation potentials and found that HF results are closed to the experiments. Electronic charge density explains the bond nature and polarization. The spin polarized electronic band profiles and density of states reveal the metallic nature of the compound. The Eu f-state splitting show that the valance bands are dominated mainly by f-[a2], f-[x(T1)], f-[y(T1)] and f-[z(T1)] states. The ground state magnetic phase of the compound is optimized. The optimum energy and magnetic susceptibility confirm the ferromagnetic nature of the compound. On the basis of different properties presented it is predicted that this compound is magnetoresistive material.