Band Structure Of Semiconductors Research Articles

Spin gating electrical current

The level of the chemical potential is a fundamental parameter of the electronic structure of a physical system, which consequently plays an important role in defining the properties of active electrical devices. We directly measure the chemical potential shift in the relativistic band structure of the ferromagnetic semiconductor (Ga,Mn)As, controlled by changes in its magnetic order parameter. Our device comprises a non-magnetic aluminum single electron channel capacitively coupled to the (Ga,Mn)As gate electrode. The chemical potential shifts of the gate are directly read out from the shifts in the Coulomb blockade oscillations of the single electron transistor. The experiments introduce a concept of spin gating electrical current. In our spin transistor spin manipulation is completely removed from the electrical current carrying channel.

Sexism may be in the eye of the beholder

Lederman and Hill reply: Perhaps Richard Wolfson would have viewed our work more favorably had he read our first book, Symmetry and the Beautiful Universe (Prometheus Books, 2004). There we championed the great mathematician Emmy Noether to the modern science lay audience. We told the story of all of physics through Noether’s grand theorem and how it forms a keystone of our understanding of nature. We did so as much to honor one of the greatest intellectuals who ever lived as to show our readership that physics is not a men’s club.More to Mr. Wolfson’s point, Victoria’s Secret stores can be found in almost every shopping mall in the US. When we pass by, we see as many women as men looking at their windows. Both genders’ thoughts may be expected to run to fantasy, yet here is a point of contact between such human experiences and physics. We are leveraging it to inspire the poetic reader to enter a world of altered reality—in this instance, to ponder the quantum world with the transmission of photons through a glass window and its inherent probabilistic nature.We hope to invite readers deeper into the magnificent world of atoms, quarks, strings, the conduction band structure of semiconductors, Schrödinger’s cat, the Dirac sea, and more. We take some risk, as we are prone to do on other topics such as politics and religion, and we have received numerous complaints concerning our belief in global warming, the creeping superstition, and anti-intellectualism that we see infecting our society today.We are inclined to disagree, however, with Mr. Wolfson’s conclusion about the effect of the Victoria’s Secret windows metaphor on our female readers: We have done the experiment of taking the risk, and we have not received a single complaint thus far from anyone else that our book is sexist.© 2012 American Institute of Physics.

Strain tuning of topological band order in cubic semiconductors

We theoretically explore the possibility of tuning the topological order of cubic diamond/zinc-blende semiconductors with external strain. Based on the tight-binding model, we analyze the evolution of the cubic semiconductor band structure under hydrostatic or biaxial lattice expansion, by which a generic guiding principle is established that lattice expansion can induce a topological phase transition of small band-gap cubic semiconductors via a band inversion, and further breaking of the cubic symmetry leads to a topological insulating phase. Using density functional theory calculations, we demonstrate that a prototype topological trivial semiconductor, InSb, is converted to a nontrivial topological semiconductor with a 2$%$--3$%$ biaxial lattice expansion.

Structural properties and quasiparticle band structures of Cu-based quaternary semiconductors for photovoltaic applications

Cu-based quaternary chalcogenide semiconductors (Cu2-II-IV-VI4) are a large group of materials that hold great promises for a variety of applications, especially as thin-film solar cell absorbers. However, despite intensive research activities, a systematic understanding of the evolution of the electronic and structural properties with chemical compositions of these materials is still lacking. In this paper, we present first-principles calculations of the structural and electronic properties of eight such semiconductors (Cu2-II-IV-VI4, with II = Zn and Cd; IV = Ge and Sn; VI = S and Se). The variation of the structural parameters with chemical compositions, investigated using the HSE06 hybrid functional, follows a few interesting trends. The quasiparticle bandgap, calculated using the state-of-the-art GW approximation, also varies systematically with chemical compositions. Effects of cation disordering on the band gaps are also investigated. This systematic understanding of the structural parameters and quasiparticle band gaps would be useful for future structural characterization and material design.

Correction: Valence State‐Dependent Ferromagnetism in Mn‐Doped NiO Thin Films

The authors regret two mistakes in Figure 1 and the Experimental Section of the above article published on the Early View platform of Advanced Materials. The correct Figure 1 is: (a) Schematic band structure of transition-metal doped oxide semiconductors with impurity bands induced by structural defects. (b) Partial DOS for NiO: (top panel) with a Ni vacancy, (middle panel) with doped Mn2+, and (bottom panel) with doped Mn3+. Further, the last section of the Experimental Section was missing the institutions at which the experiments were carried out and should read: […] The Mn K-edge X-ray absorption fine structure (XAFS) spectra were collected in fluorescence mode at room temperature at the U7C beamline of National Synchrotron Radiation Laboratory (NSRL), China. The Mn L3-edge and O K-edge X-ray absorption near-edge structure (XANES) spectra were collected in a mode of sample drain current under a vacuum better than 5 × 10−5 Pa at the U19 beamline of NSRL.

Contribution to the study of electronic structure of crystalline semiconductors (Si, Ge, GaAs, Gap, ZnTe, ZnSe)

The band structure of semiconductors was described by several theorists since the Fifties. The main objective of the present paper is to do a comparative study between various families of semi-conductors IV ( Si,Ge), III-V (GaAs, GaP) and II-VI (ZnSe, ZnTe) with both methods; tight Binding 1 method and pseudo potential method 2 . This work enables us to understand as well as the mechanism of conduction process in these semiconductors and powers and limits of the above methods. The obtained results allow to conclude that both methods are in a good agreement to describe the morphology of band structures of the cited semiconductors. This encourages us to study in the future the electronic behaviour through the structure of bands for more complex systems such as the heterostructures.

First principles investigation of dynamic performance in the process of lithium intercalation into black phosphorus

Electronic and atomic structures of LiP5, Li3P7 and LiP, which are formed in the process of lithium intercalation into black phosphorus, are systematically studied and analyzed using first-principles ultrasoft pseudopotential method based on the density functional theory (DFT). By caculating the electronic strucrures of these products, we find that the three products are all of semiconductor band structure, of which band gaps are larger than those of black phosphorus, indicating that the electronic conductivity of the black phosphorus is reduced after lithium has been intercalated into it. We simulate the diffusion of lithium ions in the LiP5, Li3P7 and LiP materials using nudged elastic band (NEB) method, and the diffusion activation energy of lithium ions is obtained firstly through the theoretical calculation. Compare with the results of other electrode materials, our results show that the migration energy barriers of lithium ions in LiP5, Li3P7 and LiP are all low. The diffusion coefficient of lithium ions in LiP5 is about 10-4 m2/s and the diffusion channel is one-dimensional. The diffusion coefficient of lithium ions in Li3P7 is approximately 10-7-10-6 cm2/s and the diffusion channel is three-dimensional. The diffusion coefficient of lithium ions in LiP is approximately 10-8-10-5 cm2/s and the diffusion channel is three-dimensional.

Amorphous Ge15Te85: density functional, high-energy x-ray and neutron diffraction study

The structure and electronic properties of amorphous Ge15Te85 have been studied by combining density functional (DF) simulations with high-energy x-ray and neutron diffraction measurements. Three models with 560 atoms have been constructed using reverse Monte Carlo methods constrained to (1) agree with the experimental structure factors S(Q), and have (2) energies close to the DF minimum and (3) a semiconducting band structure. The best structure is based on the melt-quenched DF structure and has a small number of Ge–Ge bonds. It shows interlocking networks of Te and GeTe with a significant fraction (22–24%) of voids (cavities). Ge occurs with both tetrahedral and 3 + 3 defective octahedral configurations, and the coordination of Te is slightly higher than indicated by the ‘8 − N rule’ (N is the number of valence electrons). The GeTe network includes clusters of ABAB squares (A = Ge, B = Te), and the bonding is characterized by the chemical bond orders.

Band-mixing-mediated Andreev reflection of semiconductor holes

We have investigated Andreev-reflection processes occurring at a clean interface between a $p$-type semiconductor and a conventional superconductor. Our calculations are performed within a generalized Bogoliubov-de Gennes formalism where the details of the semiconductor band structure are described by a $6\times 6$ Kane model. It is found that Andreev reflection of light-hole and heavy-hole valence-band carriers is generally possible and that the two valence-band hole types can be converted into each other in the process. The normal-reflection and Andreev-reflection amplitudes depend strongly on the semiconductor's carrier concentration and on the angle of injection. In the special case of perpendicular incidence, Andreev reflection of heavy holes does not occur. Moreover, we find conversion-less Andreev reflection to be impossible above some critical angle, and another critical angle exists above which the conversion of a heavy hole into a light hole cannot occur.

Complex Band Structures: From Parabolic to Elliptic Approximation

We show that the conventional nonparabolic approximation of real band structures can be modified and generalized to approximate the complex band structures of common semiconductors with a significant improvement of accuracy against the parabolic approximation. The improvement is due to the inherent elliptic nature of the complex band structures in the vicinity of the bandgap, which has a critical impact on the band-to-band tunneling probability. Important parameters are extracted and tabulated for Si, Ge, GaAs, and GaSb, with a maximum error of <; 1.4% compared to the numerical target.

Spin accumulation near Fe/GaAs (001) interfaces: The role of semiconductor band structure

We show that the degenerate region which forms in the vicinity of the Fe/GaAs (001) interface in Schottky tunnel barrier heterostructures plays an important role in spin transport. First, it is a prerequisite for a significant spin current to exist in the absence of an applied bias voltage, which is essential for electrical spin detection. Second, it establishes a well-defined electrochemical potential reservoir which functions as the source of spin currents flowing into the bulk of the semiconductor. A rate-equation analysis shows that the optimal thickness of the highly doped GaAs layer at the interface is in the range of 20 to 25 nm for Si dopings of $5\ifmmode\times\else\texttimes\fi{}{10}^{18}$ cm${}^{\ensuremath{-}3}$, in reasonable agreement with experiment. Both the sign and magnitude of the spin currents are sensitive to very small changes in interfacial electronic structure, as demonstrated in annealing experiments.

Isolated high-order harmonics pulse from two-color-driven Bloch oscillations in bulk semiconductors

We theoretically investigate the time-frequency characteristics of high-order harmonic generation (HHG) from Bloch-oscillating electrons in the band structure of a conventional bulk semiconductor driven by a single-optical-cycle two-color IR waveform. Spectrally filtering out the Bloch-HHG cutoff radiation allows the generation of an isolated Bloch-HHG pulse of $\ensuremath{\sim}$1.6-fs duration.

Solar Cells Using Quantum Funnels

Colloidal quantum dots offer broad tuning of semiconductor bandstructure via the quantum size effect. Devices involving a sequence of layers comprised of quantum dots selected to have different diameters, and therefore bandgaps, offer the possibility of funneling energy toward an acceptor. Here we report a quantum funnel that efficiently conveys photoelectrons from their point of generation toward an intended electron acceptor. Using this concept we build a solar cell that benefits from enhanced fill factor as a result of this quantum funnel. This concept addresses limitations on transport in soft condensed matter systems and leverages their advantages in large-area optoelectronic devices and systems.

Conduction band structure and electron mobility in uniaxially strained Si via externally applied strain in nanomembranes

Strain changes the band structure of semiconductors. We use x-ray absorption spectroscopy to study the change in the density of conduction band (CB) states when silicon is uniaxially strained along the [1 0 0] and [1 1 0] directions. High stress can be applied to silicon nanomembranes, because their thinness allows high levels of strain without fracture. Strain-induced changes in both the sixfold degenerate Δ valleys and the eightfold degenerate L valleys are determined quantitatively. The uniaxial deformation potentials of both Δ and L valleys are directly extracted using a strain tensor appropriate to the boundary conditions, i.e., confinement in the plane in the direction orthogonal to the straining direction, which correspond to those of strained CMOS in commercial applications. The experimentally determined deformation potentials match the theoretical predictions well. We predict electron mobility enhancement created by strain-induced CB modifications.

Wafer‐Scale Strain Engineering of Ultrathin Semiconductor Crystalline Layers

The fabrication of a wafer-scale dislocation-free, fully relaxed single crystalline template for epitaxial growth is demonstrated. Transferring biaxially-strained Inx Ga1-x As ultrathin films from InP substrates to a handle support results in full strain relaxation and the Inx Ga1-x As unit cell assumes its bulk value. Our realization demonstrates the ability to control the lattice parameter and energy band structure of single layer crystalline compound semiconductors in an unprecedented way.

Valence band structure of binary chalcogenide vitreous semiconductors by high-resolution XPS

High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As x Se100 − x , As x S100 − x , Ge x Se100 − x and Ge x S100 − x chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.

Electrochemical Examinations on the Corrosion Behavior of Boron Carbide Reinforced Aluminum-Matrix Composites

Galvanic corrosion of a 6092-T6 Al metal-matrix composite (MMC) reinforced with boron carbide (B4C) particulates was examined through electrochemical characterization of the MMC as well as a monolithic B4C. The results were interpreted based on a recently proposed electronic model for B4C that emphasizes a conventional non-degenerate p-type semiconductor band structure with high density of gap states. The electrochemical behavior of B4C in the dark that was characteristic of non-active metal electrodes was attributed to the very high density of gap states of B4C; while the phenomenon of the enhanced cathodic currents of B4C under illumination was attributed to the presence of a depletion layer at the B4C/electrolyte interface, characteristic of non-degenerate p-type semiconductor/electrolyte interface. The results suggested that galvanic corrosion of the MMC in the dark was limited by slow oxygen reduction kinetics at the B4C reinforcements and that illumination promotes galvanic corrosion of the MMC as a result of photo-enhanced cathodic activity of the B4C reinforcements. Scanning electron microscopy revealed that corrosion of the MMC initiated from carbon particles that are likely introduced into the matrix during the processing of the MMC. A combination of scanning vibration electrode technique and scanning ion-selective electrode technique revealed that localized anodic and cathodic sites co-exist during the corrosion of the MMC in an air-exposed 3.15 wt % NaCl solution. The localized anodic and cathodic sites have diameters of approximately 200 μm.

Theoretical investigation of atomic structure and electronic properties of Ca/Si(110)-(2 × 1) reconstruction

We have presented first-principles total-energy calculations for the adsorption of Ca metals onto a Si(110) surface. The density functional method was employed within its local density approximation to study the atomic and electronic properties of the Ca/Si(110) structure. We considered the (1×1) and (2×1) structural models for Ca coverages of 0.5 monolayer (ML) and 0.25ML, respectively. Our total-energy calculations indicate that the (1×1) phase is not expected to occur. It was found that Ca adatoms are adsorbed on top of the surface and form a bridge with the uppermost Si atoms. The Ca/Si(110)-(2×1) produces a semiconducting surface band structure with a direct band gap that is slightly smaller than that of the clean surface. One filled and two empty surface states were observed in the gap; these empty surface states originate from the uppermost Si dangling bond states and the Ca 4s states. It is found that the Ca–Si bonds have an ionic nature and complete charge being transferred from Ca to the surface Si atoms. Finally, the key structural parameters of the equilibrium geometry are detailed and compared with the available results for metal-adsorbed Si(110) surface, Ca/Si(001), and Ca/Si(111) structures.

Monte Carlo simulations of mobility in doped GaAs using self-consistent Fermi–Dirac statistics

Electron mobility as a function of ionized impurity concentration is calculated in bulk GaAs using ensemble Monte Carlo simulations. The simulations include Fermi–Dirac statistics with self-consistently calculated Fermi energy, and electron temperature which are then used in static and in random phase approximation (q-dependent) screening model and for the Pauli exclusion principle employed after each scattering event. However, when the degeneracy due to the Pauli exclusion principle is considered in the simulations, then electron mobility starts to increase at high doping concentrations demonstrating a breakdown of the model. This breakdown can be prevented by taking into account a change in the semiconductor bandstructure via dopants acting in its lattice. The bandstructure change has been incorporated by increasing electron effective mass which allows us to obtain very good agreement of simulated electron mobility with experimental data.

Ab initio calculations of surface structure and electronic properties caused by adsorption of Ca atoms on a Si(1 1 0) surface

The adsorption of Ca metals onto a Si(1 1 0) surface has been theoretically investigated by first-principle total-energy calculations. We employed a local density approximation of the density functional theory as well as a pseudopotential theory to study the atomic and electronic properties of the Ca/Si(1 1 0) structure. The (1×1) and (2×1) surface structures were considered for Ca coverages of 0.5 and 0.25 ML, respectively. It is found that the (1×1) phase is not expected to occur even for rich Ca regime. It was found that Ca adatoms are adsorbed on top of the surface and form a bridge with the uppermost Si atoms. The most stable structure of Ca/Si(1 1 0)–(2×1) surface produces a semiconducting surface band structure with a direct band gap that is slightly smaller than that of the clean surface. We have observed one filled and two empty surface states in the gap region. These empty surface states originated from the uppermost Si dangling bond states and the Ca 4 s states. Furthermore, the Ca–Si bonds have an ionic nature with almost complete charge transfer from Ca to the surface Si atoms. The structural parameters of the ground state atomic configuration are detailed and compared with the available results of metal-adsorbed Si(1 1 0) surface, Ca/Si(0 0 1), and Ca/Si(1 1 1) structures.