Splitting Of Energy Bands Research Articles

Carrier transport spin–orbit dynamics in surface enhanced Raman shift of perovskite films

The unknown LSMO/ZnO spin-orbit dynamics and bandgap are presented by Mn partial wave state density of LaSrMnO3 and SRS spectroscopy.Raman active phonon in orthorhombic perovskite ZnO/La0.7Sr0.3MnO films are were focused by measuring Raman spectra in various scattering configurations. The LSMO spin state density is modified by Mn mixed valence state. The results show that the spin–orbit is caused by anomalies tilt of MnO6 octahedron and electrons hopped into the empty orbital states. The transfer of dx2−y2 orbits dynamics is in the background of the ferro-orbital order state of crystal stabilized d3z2−r2 orbit effect. The LSMO/ZnO displays magnetic and phononic scattering measurement. The kinetic energy gain achieved by the orbital competition, magnetic ordering, strong crystal field and charge order of energy band splitting. The LSMO/ZnO junction exhibits excellent junction ​antiferromagnetic/ferromagnetic phonon peaks and magnetoresistance behavior over the temperature range of 77–300 K.The significant energy band competition originates from the strong crystal splitting field and orbital canting.

Impact of Cu–Au type domains in high current density CuInS2 solar cells

In this work, a series of stain steel 15×15cm2 CuInS2 solar cells with efficiencies close to the record one for this kind of devices, are analyzed. Through a careful and comprehensive study of the structural and electronic properties of the CuInS2 layer, we show that in a general fashion the strain originated by the thermal annealing affects the energy band splitting and reduces the short circuit current. Then, through an innovative combination of photoreflectance and Raman scattering analysis, we demonstrate that the presence of CuAu domains in the bulk layer of a CuInS2 is directly related with this strain reduction contributing to the improvement of short circuit current. We propose that the presence Cu–Au phase domains reduce the strain within the CuInS2 layer, and improve the quality of the CIS chalcopyrite crystals, leading to reduced carrier recombination while increasing carriers mobility. As a consequence we conclude that the presence of said domains improves the short circuit current in the studied devices.

Theoretical study of energy band splitting induced by spin–orbit interaction in helically coiled carbon nanotubes

Abstract Recent theoretical and experimental works on straight carbon nanotubes (SCNTs) have revealed that the curvature could enhance the spin–orbit interaction (SOI). Motivated by this, we further explore the effective SOI with another different curvature in helically coiled carbon nanotubes (HCCNTs) using the tight-binding model and perturbation approach. Finally, we derive the effective SOI in HCCNTs, and find the electron–hole asymmetric spin splitting. Interestingly, the asymmetric splitting largely depends on coil pitch p and coil radius r, which are not known in SCNTs. These results should be valuable for spintronic applications of carbon nanotubes.

Electrical conductivity enhancement by boron-doping in diamond using first principle calculations

Boron doping in diamond plays a vital role in enhancing electrical conductivity of diamond by making it a semiconductor, a conductor or even a superconductor. To elucidate this fact, partial and total density of states has been determined as a function of B-content in diamond. Moreover, the orbital charge distributions, B–C bond lengths and their population have been studied for B-doping in pristine diamond thin films by applying density functional theory (DFT). These parameters have been found to be influenced by the addition of different percentages of boron atoms in diamond. The electronic density of states, B–C bond situations as well as variations in electrical conductivities of diamond films with different boron content and determination of some relationship between these parameters were the basic tasks of this study. Diamond with high boron concentration (∼5.88% B-atoms) showed maximum splitting of energy bands (caused by acceptor impurity states) at the Fermi level which resulted in the enhancement of electron/ion conductivities. Because B atoms either substitute carbon atoms and/or assemble at grain boundaries (interstitial sites) inducing impurity levels close to the top of the valence band. At very high B-concentration, impurity states combine to form an impurity band which accesses the top of the valence band yielding metal like conductivity. Moreover, bond length and charge distributions are found to decrease with increase in boron percentage in diamond. It is noted that charge distribution decreased from +1.89 to −1.90eV whereas bond length reduced by 0.04Å with increasing boron content in diamond films. These theoretical results support our earlier experimental findings on B-doped diamond polycrystalline films which depict that the addition of boron atoms to diamond films gives a sudden fall in resistivity even up to 105Ωcm making it a good semiconductor for its applications in electrical devices.

Effects of heavy metal adsorption on silicene

Based on first-principles calculations, we study the effects of heavy metal atoms (Au, Hg, Tl, and Pb) adsorbed on silicene. We find that the hollow site is energetically favorable in each case. We particulary address the question how the adsorption modifies the band structure in the vicinity of the Fermi energy. Our results demonstrate that the heavy metal adatoms result in substantial energy gaps and band splittings in the silicene sheet as long as the binding is strong, which, however, is not always the case. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Electronic energy band structures of carbon nanotubeswith spin-orbit coupling interaction

Based on the symmetry adapted tight-binding model, the electronic energy band structures of single wall carbon nanotubes are calculated by considering the spin-orbit coupling interaction. The energy gaps at the Dirac point for the armchair nanotubes are formed due to the spin-orbit coupling interaction and the curvature effect. For the zigzag and chiral carbon nanotubes,the energy band splittings for the lowest unoccupied states and the highest occupied states are also formed by the spin-orbit coupling interaction. The energy splittings are not only dependedent on the diameter and the chiral angle of the carbon nanotubes, but also a symmetric with respect to the Fermi energy level. According to the chiral index (n, m), different tube behaviors are grouped into three families. The numeral results are in good agreement with the experimental results.

Transition metal atoms in cubic configurations

Matrix Hartree–Fock calculations are reported for 3d transition metals in a configuration chosen to represent, as closely as is possible with integral occupation numbers, an atom in an fcc metal. The cubic symmetry shell (3dt)6 is assumed to be fully occupied, and electrons are successively removed from the (3de)4 shell to represent atoms from Cu to Mn. A single 4s orbital is included, with independent calculations for the two possible choices of relative spin of the 4s orbital and 3de shell. Orbital energies are computed for each of the nonequivalent 4s and 3d orbitals, and the relationship of these quantities with transition metal energy bands is discussed. Intra-atomic orbital energy splittings are found to be comparable in magnitude to energy band splittings. Radial densities of the 4sα and 4sβ orbitals are computed. These densities are found to be compatible with a proposed explanation of recently observed negative magnetization regions within the unit cell of ferromagnetic transition metals.

Local normal-mode coupling and energy band splitting in elliptically birefringent one-dimensional magnetophotonic crystals

An analysis is presented of wave-vector dispersion in elliptically birefringent stratified magneto-optic media having one-dimensional periodicity. It is found that local normal-mode polarization-state differences between adjacent layers lead to mode coupling and affect the wave-vector dispersion and the character of the Bloch states of the system. This coupling produces extra terms in the dispersion relation not present in uniform circularly birefringent magneto-optic stratified media. Normal-mode coupling lifts the degeneracy at frequency band crossover points under certain conditions and induces a magnetization-dependent optical bandgap. This study examines the conditions for bandgap formation in the system. It shows that such a frequency split can be characterized by a simple coupling parameter that depends on the relation between polarization states of local normal modes in adjacent layers. The character of the Bloch states and conditions for maximizing the strength of the band splitting in these systems are analyzed.

First-Principles Study of Electronic Structures of MnX (X=As, Sb, or Bi): Fully Relativistic Full-Potential Calculations

We study the electronic structures of MnX (X=As, Sb, and Bi) in a ferromagnetic phase based on the density functional theory within the local spin density approximation using a fully relativistic full-potential linear-combination-of-atomic-orbitals method. In particular, we focus on the effects of spin–orbit coupling. To this end, we compare the results of the fully relativistic calculations with those of the scalar relativistic calculations. It is found that the splitting of energy bands caused by spin–orbit coupling is on the order of 0.05, 0.15, and 0.35 eV for MnAs, MnSb, and MnBi, respectively. Furthermore, we compare the results of this study with those of other theoretical studies to examine the reliability of our results.

Physics of strain effects in semiconductors and metal-oxide-semiconductor field-effect transistors

A detailed theoretical picture is given for the physics of strain effects in bulk semiconductors and surface Si, Ge, and III–V channel metal-oxide-semiconductor field-effect transistors. For the technologically important in-plane biaxial and longitudinal uniaxial stress, changes in energy band splitting and warping, effective mass, and scattering are investigated by symmetry, tight-binding, and k⋅p methods. The results show both types of stress split the Si conduction band while only longitudinal uniaxial stress along ⟨110⟩ splits the Ge conduction band. The longitudinal uniaxial stress warps the conduction band in all semiconductors. The physics of the strain altered valence bands for Si, Ge, and III–V semiconductors are shown to be similar although the strain enhancement of hole mobility is largest for longitudinal uniaxial compression in ⟨110⟩ channel devices and channel materials with substantial differences between heavy and light hole masses such as Ge and GaAs. Furthermore, for all these materials, uniaxial is shown to offer advantages over biaxial stress: additive strain and confinement splitting, larger two dimensional in-plane density of states, smaller conductivity mass, and less band gap narrowing.

Straining of monocrystalline silicon thin films with the use of porous silicon as stress generating nanomaterial

A simple and low cost technological approach for the straining of thin crystalline silicon (Si) films using porous silicon (PS) as stress generating nanomaterial is reported. Structural analysis of the PS∕Si structures is performed by transmission electron microscopy. Raman scattering spectroscopy is used for the evaluation of stress and strain values in the strained thin Si films. Depending on the thickness of the strained Si films, the maximum strain values are found to be in a range from 1% to 1.4%. Various modifications of electronic properties of the strained Si films are observed by photoluminescence spectroscopy. For example, strain induced redshift of the Si energy band gap and splitting of the valence band are detected.

Field Dependence of Spin Lifetimes in Wurtzite Materials

We present first-principles calculations of the zero field spin splitting of energy bands in wurtzite materials. Our calculations reveal that the huge electric fields originating from strong piezoand pyroelecric character of nitrides do not increase the spin splitting of bands in nitride heterostructures. This implicates long spin lifetimes in quantum structures based on these materials and weak possibility of tuning with external electric field.

Resonant Spin Splitting in III-V Semiconductors

We present flrst-principles studies of the zero fleld spin splitting of energy bands in typical III{V semiconductors. Our calculations reveal that the strain induces linear-k spin splitting of the conduction band in the i point, which is linear in strain, and determine the magnitude of the so-called acoustic phonon constant that characterizes the magnitude of the spin splitting. In addition, we show that optical phonons lead to spin-∞ip processes and we present quantitative results for the spin-phonon deformation potentials in GaAs. Most importantly, the calculations show that the linear-k spin splitting can be resonantly enhanced when bands cross in a particular point of the Brillouin zone. This resonant enhancement of the bulk inversion asymmetry coupling constant by more than one order of magnitude was observed in both valence and conduction bands and can be steered by the application of the external stress. This allows tailoring of the spin relaxation and spin precession of conduction electrons in nanostructures to a much larger extent than was hitherto assumed.

Band gap energy and valence band splitting of p-CdIn2Te4 crystal by photocurrent spectroscopy

Single crystals of p-CdIn2Te4 were grown by the Bridgman method without a seed crystal. From photocurrent measurements, it was found that three peaks, A, B, and C, correspond to the intrinsic transition from the valence band states of Γ7(A), Γ6(B), and Γ7(C) to the conduction band state of Γ6, respectively. The crystal field splitting and the spin orbit splitting were found to be 0.2360 and 0.1119 eV, respectively. The temperature dependence of the CdIn2Te4 band gap energy was given by Eg(T)=Eg(0)−(9.43×10−3)T2/(2676+T). The Eg(0) was calculated to be 1.4750, 1.7110, and 1.8229 eV at the valence band states of Γ7(A), Γ6(B), and Γ7(C), respectively. The band gap energy of p-CdIn2Te4 at room temperature was determined to be 1.2023 eV.

Band structure ofCdGeAs2near the fundamental gap

First-principles band structure calculations were carried out for the chalcopyrite semiconductor ${\mathrm{CdGeAs}}_{2}$ using the linear muffin-tin orbital method, including spin-orbit coupling. The emphasis of the analysis is on the band gaps and energy band splittings near the fundamental gap. The gap underestimate due to the local-density approximation is corrected using information on quasiparticle calculations for the parent compound GaAs. The experimental information on optical transitions near the gap is reviewed critically in the light of our calculations. The polarization dependence and the pseudodirect nature of some of the transitions is discussed. The effective masses of the conduction band and valence bands are derived from the calculated band structure. A generalization of the Luttinger Hamiltonian for chalcopyrite is presented and its parameters determined.

Influence of effective mass and energy band splittings on the radiative characteristics of QW lasers at transparency

The effect of degenerate light- and heavy-hole bands on the carrier and current density and the differential gain are studied and compared with the nondegenerate case in semiconductor quantum-well (QW) lasers. It is demonstrated that the presence of the degenerate bands at the valence band (VB) maximum will always lead to an increased threshold radiative current density compared to the case where only one band is significantly populated. When the valence bands are separated by an energy E s, the current density decreases rapidly with increasing E s, with greater reductions being achieved for a given tensile than compressive strain. The effect of the second subband becomes less important with increasing E s, and the radiative current density reverts to that of the one VB case, demonstrating the importance of maximising the subband energy separation to optimize laser characteristics.

Shifts and splitting of energy bands in elastically strained InGaP/GaAs(111)B epitaxial films

Strain-induced shifts and splitting of energy bands are studied by optical techniques in compressively strained pseudomorphic InxGa1−xP films grown by liquid phase epitaxy on lattice-mismatched GaAs(111)B substrates. The elastic strains are measured by the x-ray diffraction technique and reach the value of 0.92%. The splitting of the valence band is revealed as a doublet in the derivative of a photocurrent spectrum which is precisely measured on the semiconductor-electrolyte interface near the fundamental absorption edge. The maximum splitting reaches 45 meV. The sublinear behavior of the valence band splitting versus elastic strain is clearly observed. This nonlinearity is explained by the interaction between the strain-split subband with J=3/2, mJ=±1/2 and the spin-orbit split subband (J=1/2, mJ=±1/2). The experimentally measured dependences of shifts and splitting on the magnitude of strain are well described by the theoretical calculations.

The Effect of the Electron–Phonon Interaction on Giant Magnetoresistance in Magnetic Multilayers11The project supported by National Natural Science Foundation of China

We built electron and phonon free energies and attempted to investigate the effect of the electron–phonon interaction on giant magnetoresistance in magnetic multilayers. Starting from a jellium-like model, we found that the electron–phonon interaction can have an important effect on the spin splitting of electronic energy band. The expression of giant magnetoresistance has been obtained by considering the spin splitting of electronic energy band, indicating that the effect of phonon could not be neglected. Numerical calculations using our approach demonstrate the agreement between experimental and theoretical values.

First-principles studies of the structural and optical properties of crystalline poly(para-phenylene).

We present first-principles local-density band structure calculations for one-dimensional and three-dimensional crystalline poly (para-phenylene) (PPP) using the full-potential linearized augmented-plane-wave and the pseudopotential methods. Optimized structural parameters for PPP chains and for orthorhombic crystalline phases with space groups Pbam and Pnnm are determined. A torsion angle of 27\ifmmode^\circ\else\textdegree\fi{} is predicted in PPP chains and 17\ifmmode^\circ\else\textdegree\fi{} in the crystals. The dielectric tensor and the absorption coefficient are calculated. We find very good agreement with experimental data, indicating that the excitations are extended band states. The interchain coupling leads to energy band splittings of the order of 0.5 eV. It is shown that the energy gap can be varied over a wide energy range by relatively small structural modifications.

The effect of the electron-phonon interaction on the spin splitting of electron energy bands in an itinerant electron ferromagnet

We report our discovery that the exchange splitting of the electron energy bands in the ferromagnetic state of a metal can be affected by the effect of the electron-phonon interaction and that, whereas the sign and magnitude of such a phonon effect depend sensitively on the electronic structure around the Fermi surface of the metal, the magnitude can be comparable with that of the ordinary Stoner exchange splitting. This conclusion was obtained by examining how the phonon frequencies, and therefore the phonon free energy, change with the spin splitting of the energy bands of the screening electrons in an itinerant electron ferromagnet. By carrying out a numerical calculation with a model electronic density of states, we demonstrate the importance of considering this effect in accounting for the observed magnetization and its temperature dependence in a ferromagnetic metal.