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The temperature-dependence of the electrical and dielectric properties of paper substrates was studied using experimental papers with different NaCl contents, different thicknesses, and different grammages. Physical processes related to the charging potential, charge decay rate, conductivity, dielectric constant, and dielectric loss of papers are dependent on thermal energy, and this dependence on temperature can be described by exponential expressions. The ion content of paper not only determines the level of these properties at a given temperature, as expected but also influences their temperature-dependence. Frequency analysis of the dielectric loss confirms that new structures are formed in paper by the addition of NaCl. The results may be applicable to the design of materials and equipment, e.g., for the electrophotographic printing processes.

Suspended graphene has the highest measured thermal conductivity of any material at room temperature. However, when graphene is supported by a substrate or encased between two materials, basal-plane heat transfer is suppressed by phonon interactions at the interfaces. We have used frequency domain thermoreflectance to create thermal conductance maps of graphene contacts, obtaining simultaneous measurements of the basal-plane thermal conductivity and cross-plane thermal boundary conductance for 1–7 graphitic layers encased between titanium and silicon dioxide. We find that the basal-plane thermal conductivity is similar to that of graphene supported on silicon dioxide. Our results have implications for heat transfer in two-dimensional material systems, and are relevant for applications such as graphene transistors and other nanoelectronic devices.

We have been observing the kinetic buildup of electrical conduction current upon x-ray irradiation in ZnSe single crystals. The objective is to understand the behavior of ZnSe crystals under x-ray irradiation, toward their potential use in x-ray detectors that do not require cooling and can operate above room temperature. The paper focuses on the factors that affect the behavior of traps at room temperature. A model is developed to understand the origin of the behavior of the conduction current under x-ray irradiation, taking into account the contributions from three types of traps for electrons (shallow, phosphorescent, and deep) and two luminescence centers (luminescence bands of 630 and 970 nm). Principally, the model is applied to the fitting of the experimental curves. Consequently, the work puts in evidence the role of electron accumulation on traps on the x-ray conduction current buildup on ZnSe crystals. We have obtained experimental dependencies of x-ray conduction current buildup current at 85 K, which indicates the presence of delay in comparison with x-ray luminescence buildup. This paper will demonstrate the effectiveness of our theoretical method in the framework of the multi-center model for wide-gap semiconductors.

In this work, we report on the emergence of a photonic Hall effect (PHE) system within a narrow filtered background of a one-dimensional defective optical dielectric structure with graphene under the influence of a constant magnetic field regime. It is observed that at low temperature and relatively strong applied magnetic fields, electromagnetic defective transmission spectra corresponding to the two decoupled right- and left-handed polarized modes possess a step-like transmission feature which is referred to as “quantum Hall defect modes” (QHD modes or QHDs) in this paper. Tunable growing transitional transmission steps for QHDs with increasing magnetic field intensity were shown to be possible. Observation of sensitive magneto-transmission oscillations to the thermal excitations in the last plateaus slowly ascending toward unity is another special feature noted in this work. The results of this study, which is carried out based on rapid standard calculations for the transfer matrix approach is supplied with commercial simulations marking the first PHE system, promise an proper candidate for new photonic applications, especially new tunable magneto-based lenses and photonic magneto-thermal sensors.In this work, we report on the emergence of a photonic Hall effect (PHE) system within a narrow filtered background of a one-dimensional defective optical dielectric structure with graphene under the influence of a constant magnetic field regime. It is observed that at low temperature and relatively strong applied magnetic fields, electromagnetic defective transmission spectra corresponding to the two decoupled right- and left-handed polarized modes possess a step-like transmission feature which is referred to as “quantum Hall defect modes” (QHD modes or QHDs) in this paper. Tunable growing transitional transmission steps for QHDs with increasing magnetic field intensity were shown to be possible. Observation of sensitive magneto-transmission oscillations to the thermal excitations in the last plateaus slowly ascending toward unity is another special feature noted in this work. The results of this study, which is carried out based on rapid standard calculations for the transfer matrix approach is supplied...

The electromagnetic field generated by a horizontal electric dipole in the air over a dielectric‐coated conducting or dielectric half‐space is evaluated in an earlier paper subject to the conditions k20≪k21≪‖k22‖ on the wave numbers of the three regions and the condition k1l≤ 0.6 on the thickness l of the dielectric layer. Unintentionally, the severe condition ‖k2 l‖2≪1 was also imposed in the determination of the field in the dielectric layer and the half‐space below it. That restriction is removed in this paper and new complete formulas are derived which have wide potential application.

In a recent paper Yokoyama [Mol. Cryst. Liq. Cryst. 165, 265 (1988)] showed that a correct thermodynamic definition of the anchoring energy at the interface between a nematic liquid crystal (NLC) and another medium requires the preliminary choice of a ‘‘Gibbs dividing surface.’’ As a consequence of this, the measured value of the anchoring energy coefficient can depend on which method is used to perform the experiment. This dependence probably explains the large discrepancies that are often reported in the literature between anchoring energy coefficients measured on the same substrate by different authors. To test this important point the anchoring energy coefficient at a SiOx nematic interface has been measured by using two different methods at the same time: a reflection light method and a transmitted light method. Both these methods have been already used in the literature. In this paper the latter method is analyzed in detail and it is shown that its accuracy is greatly reduced by the presence of spurious bulk contributions. To increase accuracy, a new experimental procedure is proposed that exploits the differing dependence of surface and bulk contributions on the intensity of the magnetic field. This new method allows one to separate bulk and surface contributions without using fitting procedures. Therefore both the anchoring energy and information on the bulk director distortion can be directly obtained from the experiment. The transmitted light and the reflected light methods are used simultaneously to measure the azimuthal anchoring energy coefficient at the SiOx nematic interface on the same NLC sample at the same temperatures. A satisfactory agreement between the anchoring energy coefficients measured by the two methods is found.

This paper provides a detailed description explaining how to calculate the relation between the silicon Raman frequency and local stress or strain in the silicon, applied to stress measurements in microelectronics. This relation is well known for measurements from the (100) surface of silicon. However, it is often used in the wrong way, neglecting non-zero stress tensor elements. Especially, in current 3D microelectronics technology, where the stress caused by through Si vias or micro-bumps is of large importance, the vertical stress component, which highly affects the measured Raman frequency shift, is often erroneously neglected. In addition, the equations for the (100) surface are also often used incorrectly for cross-sectional measurements from a (110) surface. In this paper, different ways to calculate the relation between Raman frequency and triaxial stress, and the related Raman peak intensities, are discussed in detail.

Three papers published recently [P. M. Young, C. H. Grein, H. Ehrenreich, and R. H. Miles, J. Appl. Phys. 74, 4774 (1993); G. M. Williams, J. Appl. Phys. 77, 4153 (1995); C. H. Grein, M. E. Flatte, H. Ehrenreich, and R. H. Miles, J. Appl. Phys. 77, 4156 (1995)] concerning the comparison of theoretically predicted performance of HgCdTe photodiodes with InAs/InGaSb superlattice photovoltaic detectors are obscure with respect to optimal selection of HgCdTe photodiode structures. Both Comments [G. M. Williams, J. Appl. Phys. 77, 4153 (1995); C. H. Grein, M. E. Flatte, H. Ehrenreich, and R. H. Miles, J. Appl. Phys. 77, 4156 (1995)] have not noticed the important results of papers published by Humpreys [Infrared Phys. 23, 171 (1983); Infrared Phys. 26, 337 (1986)], who critically reexamined the role of a radiative mechanism in the detection of infrared radiation. To explain our point of view on competition between InAs/InGaSb SLs and ‘‘bulk’’ HgCdTe detectors, we present a generalized model of an infrared photo...

This paper theoretically and numerically investigates the propagation of Lamb waves in a one-dimensional phononic crystal slab bordered with anti-symmetric boundary layers. The results show that the band structure of the anti-symmetric boundary phononic crystal is significantly different from those presented in the papers available. The eigenmodes displacement fields reveal that there is an essential distinction in the formation of the band gap between the anti-symmetric and the symmetric boundary model. On the other hand, the thickness of the boundary layers can remarkably change the width and the location of the band gaps. Furthermore, the variation of the phononic crystal band gaps and the band pinning elimination show the band gaps are sensitive to the degree of stagger of the boundary layers, and different band gap has a different response to the profile of the boundary. In other words, the topological distribution of the boundary layer has an influence on the band structures.

In this paper we study the bandgap properties of two-dimensional phononic crystals with cross-like holes using the finite element method. The influence of the geometry parameters of the holes on the bandgaps is discussed. In contrast to a system of square holes, which does not exhibits bandgaps if the symmetry of the holes is the same as that of the lattice, systems of cross-like holes show large bandgaps at lower frequencies. The bandgaps are significantly dependent upon the geometry (including the size, shape, and rotation) of the cross-like holes. The vibration modes of the bandgap edges are computed and analyzed in order to clarify the mechanism of the generation of the lowest bandgap. It is found that the generation of the lowest bangdap is a result of the local resonance of the periodically arranged lumps connected with narrow connectors. Spring-mass models are developed in order to predict the frequencies of the lower bandgap edges. The study in this paper is relevant to the optimal design of the bandgaps in light porous materials.

This paper reports a detailed experimental analysis on the effect of forbidden bandgaps of planar metallo-dielectric electromagnetic bandgap (EBG) structures as ground plane of a half wavelength linear resonator. It is observed that the resonator with metallic square and triangular lattice as ground plane results in resonance shifting to higher values whereas, on patterning negative structures of the said lattice which we mention as dielectric lattice in this paper, did not result in any appreciable change. Simulation and experimental results illustrate appreciable increase in quality factor and decrease in insertion loss for metallic EBG on the ground plane, while marginal reduction in insertion losses and increase in quality factor has been obtained with dielectric lattice.

The aim of the paper is to describe the modes coupling due to scattering on small one-dimensional irregularities (parallel ridges) of the surface of isotropic solid plates, when shear horizontal waves (SH-waves) polarized along the ridges propagate perpendicularly to them. In a previous paper [Valier-Brasier et al., Appl. Phys. Lett. 93, 164101 (2008)], an analytical model was presented for describing the roughness by inertia of “teeth” which bound the ridges, through an impedancelike boundary condition, whatever shape of the roughness is. In the present paper, this shape is accounted for through a more sophisticated model, used previously for describing the effects of the roughness of walls on acoustic pressure fields in fluid-filled waveguides [Valier-Brasier et al., J. Appl. Phys. 106, 034913 (2009)], and adapted here in order to describe the modes coupling due to the scattering of these SH-waves. Moreover, the effect of a spatial periodicity of the ridges on the modes coupling is discussed, emphasizin...

Evanescent modes in complete sonic crystals (SCs) and SC with point defects are reported both theoretically and experimentally in this paper. Plane wave expansion (PWE) and in general, ω(k)ω(k) methods have been used to calculate band structures showing gaps that have been interpreted as ranges of frequencies where no real kk exists. In this work, we extend PWE to solve the complex k(ω)k(ω) problem applied to SC, introducing the supercell approximation for studying one vacancy. Explicit matrix formulation of the equations is given. This k(ω)k(ω) method enables the calculation of complex band structures, as well as enabling an analysis of the propagating modes related with real values of the function k(ω)k(ω), and the evanescent modes related with imaginary values of k(ω)k(ω). This paper shows theoretical results and experimental evidences of the evanescent behavior of modes inside the SC band gap. Experimental data and numerical results using the finite elements method are in very good agreement with the predictions obtained using the k(ω)k(ω) method., The authors would like to thank Dr. E. A. Sanchez-Perez for his comments and suggestions and thank Daniel Fenollosa and Talleres Ferriols for their help in building the mechanical part of 3DReAMS. This work was supported by MEC (Spanish government) and the European Regional Development Fund, under Grant Nos. MAT2009-09438 and MTM2009-14483-C02-02.

This thesis work aims at a better understanding of magneto-optical properties of dilute nitrides and II-VI diluted magnetic semiconductor quantum structures. The thesis is divided into two parts. The first part gives an introduction of the research fields, together with a brief summary of the scientific results included in the thesis. The second part consists of seven scientific articles that present the main findings of the thesis work. Below is a short summary of the thesis. Dilute nitrides have been of great scientific interest since their development in the early 1990s, because of their unusual fundamental physical properties as well as their potential for device applications. Incorporation of a small amount of N in conventional Ga(In)As or Ga(In)P semiconductors leads to dramatic modifications in both electronic and optical properties of the materials. This makes the dilute nitrides ideally suited for novel optoelectronic devices such as light emitting devices for fiber-optic communications, highly efficient visible light emitting devices, multi-junction solar cells, etc. In addition, diluted nitrides open a window for combining Si-based electronics with III-V compounds-based optoelectronics on Si wafers, promising for novel optoelectronic integrated circuits. Full exploration and optimization of this new material system in device applications requires a detailed understanding of their physical properties. Papers I and II report detailed studies of effects of post-growth rapid thermal annealing (RTA) and growth conditions (i.e. presence of N ions, N2 flow, growth temperature and In alloying) on the formation of grown-in defects in Ga(In)NP. High N2 flow and bombardment of impinging N ions on grown sample surface is found to facilitate formation of defects, such as Ga interstitial (Gai) related defects, revealed by optically detected magnetic resonance (ODMR). These defects act as competing carrier recombination centers, which efficiently decrease photoluminescence (PL) intensity. Incorporation of a small amount of In (e.g. 5.1%) in GaNP seems to play a minor role in the formation of the defects. In GaInNP with 45% of In, on the other hand, the defects were found to be abundant. Effect of RTA on the defects is found to depend on initial configurations of Gai related defects formed during the growth. In Paper III, the first identification of an interfacial defect at a heterojunction between two semiconductors (i.e. GaP/GaNP) is presented. The interface nature of the defect is clearly manifested by the observation of ODMR lines originating from only two out of four equivalent orientations. Based on its resolved hyperfine interaction between an unpaired electronic spin (S=1/2) and a nuclear spin (I=1/2), the defect is concluded to involve a P atom at its core with a defect/impurity partner along a direction. Defect formation is shown to be facilitated by N ion bombardment. In Paper IV, the effects of post-growth hydrogenation on the efficiency of the nonradiative (NR) recombination centers in GaNP are studied. Based on the ODMR results, incorporation of H is found to increase the efficiency of the NR recombination via defects such as Ga interstitials. In Paper V, we report on our results from a systematic study of layered structures containing an InGaNAs/GaAs quantum well, by the optically detected cyclotron resonance (ODCR) technique. By monitoring PL emissions from various layers, the predominant ODCR peak is shown to be related to electrons in GaAs/AlAs superlattices. This demonstrates the role of the SL as an escape route for the carriers confined within the InGaNAs/GaAs single quantum well. The last two papers are within a relatively new field of spintronics which utilizes not only the charge (as in conventional electronics) but also the quantum mechanical property of spin of the electron. Spintronics offers a pathway towards integration of information storage, processing and communications into a single technology. Spintronics also promises advantages over conventional charge-based electronics since spin can be manipulated on a much shorter time scale and at lower cost of energy. Success of semiconductor-based spintronics relies on our ability to inject spin polarized electrons or holes into semiconductors, spin transport with minimum loss and reliable spin detection. In Papers VI and VII, we study the efficiency and mechanism for carrier/exciton and spin injection from a diluted magnetic semiconductor (DMS) ZnMnSe quantum well into nonmagnetic CdSe quantum dots (QD’s) by means of spin-polarized magneto PL combined with tunable laser spectroscopy. By means of a detailed rate equation analysis presented in Paper VI, the injected spin polarization is deduced to be about 32%, decreasing from 100% before the injection. The observed spin loss is shown to occur during the spin injection process. In Paper VII, we present evidence that energy transfer is the dominant mechanism for carrier/exciton injection from the DMS to the QD’s. This is based on the fact that carrier/exciton injection efficiency is independent of the width of the ZnSe tunneling barrier inserted between the DMS and QD’s. In sharp contrast, spin injection efficiency is found to be largely suppressed in the structures with wide barriers, pointing towards increasing spin loss.

This paper deals with the calculation of the thermal transport cross section and phase function of transverse phonons for scattering by nano and micro particles. Thermal transport cross section is different than the scattering cross section due to the anisotropic nature of scattering. Exact formulation of the phase function is given for the Rayleigh scattering. This paper also proposes an approximate method to calculate the thermal transport cross section for low contrast scatterer. It is also shown that for SH (horizontally shear) phonons the scattering and transport cross sections are proportional to ω8 rather than the well accepted value of ω4 in the Rayleigh regime where ω is the frequency of the SH phonons. The formulations developed in this paper will be useful for the predictive modeling of thermal conductivity of practical systems such as nano composites, nano-micro particle laden systems etc.

The domain structure of ferroelectric ceramics can be altered by the process of electrical poling. This paper develops quantitative approaches for reflection geometry and spherical harmonic texture analysis, both of which describe these changes at angles parallel to and tilted from the poling axis. The x-ray-diffraction approach uses the relative intensity ratio of ferroelectric poles in poled and unpoled lead zirconate titanate to calculate a domain switching fraction (η) or a multiple of a random distribution, which are shown to be linearly related. An x-ray area detector diffractometer was used for these measurements, although the technique applies to any x-ray reflection geometry. The neutron-diffraction approach employs a Rietveld refinement with a spherical harmonic texture model. Both approaches calculate similar domain textures for two poling fields and the small differences between the approaches can be attributed to surface domain texture. This paper shows that the March–Dollase pole distributio...

In this paper, we investigate the formation of a photonic terajet and tune its optical properties using the high-resolution finite-difference time-domain method. A Dirac semimetal is coated onto the surface of a dielectric rod and illuminated with an incident plane wave. The refractive index of the Dirac semimetal can be modulated by changing its Fermi energy. It was demonstrated that the presence of the Dirac semimetal layer can significantly affect the characteristics of the photonic terajet, such as focal distance, intensity, full-width at half maximum, and length.

Two-dimensional (2D) GaS, GaSe, and InSe were reported to be semiconductors and have been recently fabricated with potential applications in photoelectrics, where in-depth understanding from electronic structure is necessary. In addition, the thermal transport properties play a key role as to the thermal stability and the efficient heat dissipation for device operation, which are also necessary to be addressed. In this paper, we present a systematic first-principles study on the electronic, optical, and thermal transport properties for the representative group III–VI monolayer GaS, GaSe, and InSe. Our results indicate that monolayer GaS, GaSe, and InSe are semiconductors with an indirect bandgap. The predominant influence of interband transitions due to the large bandgap causes monolayer GaSe to possess the highest absorptivity along both “in-plane” and “out-of-plane” directions compared to the other two systems. Moreover, the lattice thermal conductivities (κL) of these materials are found to be inversely proportional to their average atomic mass, but the decrease in thermal conductivity from GaS to GaSe is negligible in comparison to that of GaSe to InSe with a nearly equivalent mass difference. It is found that the underlying mechanism lies in the larger phonon relaxation time of GaSe caused by weaker anharmonicity. Our study provides a comprehensive understanding of the inherent physical properties of monolayer GaS, GaSe, and InSe, which would benefit their future applications in photoelectrics.

In this paper, the strain gradient is introduced to tune the semiconducting performance of piezoelectric semiconductor (PSC) nanowires by changing their cross sections. A one-dimensional model of the PSC nanowire with a non-homogeneous cross section under axial extension is established. The combined influences of piezoelectricity and flexoelectricity resulting from the strain gradient are taken into account. Approximate closed-form solutions for the distribution of carriers and electromechanical fields of the PSC nanowire are given. The effects of strain gradient, flexoelectricity, and initial carrier concentration on the distribution of carriers, electric field, electric potential, and displacement are discussed. It is observed that non-homogeneous PSC nanowires show strong size-dependent behaviors in connection with their cross-sectional diameters. The strain gradient and flexoelectric effect enhance the electromechanical coupling effect. This research provides a new way to tune inner carrier distributions and electromechanical characteristics for piezoelectric semiconductor devices.

Natural gases have played a significant role in different sectors of the global economy. Recent analyses have shown that the world's gas consumption doubled over the last three decades; further growth of the gas consumption is predicted, rising to be 23%–28% of the total primary energy demand by 2030. Therefore, liquefaction of natural gases rapidly gains global importance. In this context, magnetic refrigeration emerges as a modern energy-saving technique, which is an alternative to the traditional gas-compression refrigeration. This paper is devoted to the study of the magnetocaloric effect in magnetic fields up to 10 T on a representative of the Laves phase alloys, GdNi2, which is considered as a perspective material for liquefaction of natural gases. For a magnetic field change of 10 T, the magnetic entropy change ΔSm ≈ −17 J/kg K and the adiabatic temperature change ΔTad ≈ 6.8 K was attained around Curie temperature TC = 70 K. The maximal value of the adiabatic temperature change measured directly in pulsed magnetic fields up to 50 T is ΔTad ≈ 15 K.

One-dimensional piezoelectric semiconductor (PSC) nanowires have been widely used in smart structures and devices; however, few theoretical studies on their nano-size effects have been carried out. In this paper, a theoretical analysis of one-dimensional n-type PSC nanowires under an axial force was carried out, with consideration of the flexoelectric and strain gradient effects. Exact solutions were obtained based on the differential operator theory. The flexoelectric and strain gradient effects on the internal electromechanical field and carrier concentration have been discussed. It can be shown that the flexoelectric effect weakens the piezoelectricity of a PSC nanowire while the strain gradient has the opposite effect, with an amplitude enhancement that is dependent on the flexoelectric and inner scale coefficients.

The occurrence of localized destructive breakdown (LDB) is a feature of direct coupled thin‐film electroluminescence (DCTFEL) which has been attributed in the past to variations in applied field or threshold voltage caused by geometrical artifacts introduced during film deposition. However, in a companion paper it has been reported that this view of LDB is inconsistent with observations; instead there are strong indications that both LDB and DCTFEL are natural consequences of dielectric breakdown in ZnS:Mn. In this paper, the O’Dwyer theory of dielectric breakdown is applied to DCTFEL in ZnS:Mn with the aid of a simple computational equilibrium model. It is found that with reasonable assumed values for basic electronic parameters, current‐controlled negative resistance (CCNDR) is expected in the normal DCTFEL current density regime. Localized (filamentary) conduction is, of course, a well‐known consequence of CCNDR and the profound implications of this for EL are explored in some detail. It becomes clear ...

Electric fields associated with the space‐charge layer at the surface of silver halide grains are expected to have a marked effect on the photographic properties of emulsions. The purpose of this paper is to describe a new method based on dielectric measurements to obtain information on the surface layers. It is shown that the surface layers have a strong effect on the low‐frequency dielectric constant so that it is possible to derive the properties of the former from measurements made on the latter. Formulas connecting the layer properties to the dielectric constant of the crystal are derived. The experimental results, obtained with the method described here, will be the subject of a separate paper.

The fabrication of a planar guard ring diode which exhibits uniform microplasma‐free breakdown is described. Discrepancies are discussed between the behavior of these junctions and those reported by Batdorf et al. and Chynoweth, including results showing extremely hard V‐I characteristics associated with uniform avalanche breakdown. Experimental evidence is presented which confirms Shockley's theory in which the breakdown behavior is predicted from the Poisson distribution of impurities within the space‐charge layer. The photomultiplication technique as described in Paper I is applied to uniform p—n junctions. The linearity of 1/M vs V, as predicted by theory, was verified for values of M between 1.6 and 500. For higher values, the multiplication curves deviate from a straight line. In this higher range they are in good agreement with the pulse‐multiplication model developed in Paper I. Light emission patterns from these junctions are shown and a correlation between these patterns and crystal properties is discussed. The effects of resistivity striations in the silicon single crystals is shown to have a strong effect on breakdown areas and no effects of dislocations and oxygen on uniformity are found. From capacity and multiplication measurements a value for the breakdown field of EB=445±25 kV/cm was obtained for a 32‐V junction.

The noise spectrum due to fluctuations of electron‐hole pairs in a semiconductor in the presence of a magnetic field when ambipolar drift and generation recombination are the only important noise processes was presented in a previous paper. In this paper the noise spectrum is presented for the opposite case when ambipolar diffusion and generation recombination are the important processes with ambipolar drift being negligible and unimportant. This spectrum was obtained via the Green's function for the macroscopic differential equation which governs the behavior of the conditional average for fluctuations in the electron‐hole‐pair particle density when ambipolar diffusion and generation recombination are the only important noise processes. From the obtained result for the spectrum, numerical calculations were carried out in order to display the functional dependence of the noise spectrum on frequency and magnetic field strength for fixed ratios of the mean volume lifetime of electron‐hole pairs to the characteristic ambipolar diffusion time of electron‐hole pairs along the direction of the magnetic field. Finally, it is shown that for high frequencies the asymptotic dependence of the spectrum on frequency obeys the ``universal 3/2 power law''.

Nonmagnetic semiconductor based magnetoresistance (MR) devices combining high performance and low cost have attracted a lot of attention. However, it has been a great challenge to separate the interface MR from the bulk MR in the devices composed of Schottky heterojunctions. In this paper, the MR effect of a silicon-based Schottky heterojunction device had been studied, and its mechanisms were investigated by separating the interface MR effects from the bulk MR effects through combining two-probe and four-probe methods. We find that the bulk MR value is significantly smaller than the total MR value in the avalanche breakdown region in the temperature range of 150 K to 300 K, indicating that the total MR effect mainly originates from the interface MR effect. Theoretical analysis shows that the bulk MR effect is a normal one due to the existence of the Lorentz force on the carriers, and the interface MR effect relates to the suppression of the local plasmas by applying magnetic fields, where the local plasmas form due to the avalanche breakdown in the Ag/SiO2/p-Si Schottky heterojunctions. The total MR effect at room temperature can be further enhanced by reducing the distance between electrodes, and the total MR reaches about 1847% under a magnetic field of 1 T and the MR sensitivity is as large as 118.5 T−1 under 0.1 T.

Understanding photogenerated carrier transport dynamics is important for optimizing the performance of various semiconductor optoelectronic devices, such as photocatalysts, solar cells, and radiation detectors. In this paper, the spatiotemporal evolution of photogenerated carriers after excitation is investigated both analytically and numerically, in order to reveal the origin of two contradictory photocarrier motion directions, i.e., separation and ambipolar transport in the semiconductors. An analytical solution of the separation distance between mean positions of photogenerated electrons and holes is derived, which shows that photocarriers will transport ambipolarly in the lifetime regime, where the carrier lifetime τ 0 is larger than the dielectric relaxation time τ d, and separate spontaneously in the relaxation regime, where τ 0 < τ d. Numerical simulation verifies the analytical results and reveals rich dynamics of carrier transport near the boundary of two regimes. In the lifetime regime, the separation distance rises asymptotically to a polarization distance, while there is a transitional sub-region near the regime boundary where majority carriers go through a separating-ambipolar transformation dynamics. This phenomenon originates from two different components of the drift current. In the relaxation regime, majority carriers deplete because of a larger recombination rate in the minority carrier pulse region. Combining the analytical and numerical results, detailed photocarrier transport dynamics are obtained in the lifetime and relaxation regimes of semiconductors.

Ti0.5Zr0.25Hf0.25NiSn provides a high dimensionless figure of merit (ZT) of 1.2 at a mid-range temperature for an n-type half-Heusler thermoelectric (TE) material, which is our motivation for this study. In this paper, we present theoretical studies of the electronic structure and TE properties of a transition metal (TM) co-doped Ti-site of TiNiSn with the formula Ti0.5TMI0.25TMII0.25NiSn, where TM is Sc, Zr, Hf, V, Nb, or Mn. The calculated Lowdin charges showed that the TM had given a charge to the Ti atom and had affected the Ti-d state in the partial density of state (PDOS). The band structure and PDOS showed that co-doping with ZrNb, ZrV, HfV, HfNb, VNb, ScMn, ZrMn, or HfMn created electron-pockets in the Fermi energy level (EF) and conduction band. The TiNiSn, ScV, ScNb, and ZrHf show a large S that indicates semiconductor behavior, while ScMn, ZrV, ZrNb, ZrMn, HfV, HfNb, HfMn, and VNb show a very narrow S that indicates metal-like behavior due to the electron-pocket. The calculated lattice thermal conductivity of TiNiSn is 4.8 W m−1 K−1, which decreased to 4.27–2.42 W m−1 K−1 when co-doped with TM. The electron-pocket case shows a low ZT due to the low power factor at EF. The calculated ZT of TiNiSn shows a high value of 0.2–0.24 at around EF. The highest power factor contributing low thermal conductivity yielded a high ZT of 0.24–0.34 for ScV, 0.33–0.42 for ScNb, and 0.33–0.39 for ZrHf, at around EF.

This paper examines the structural properties of gallium phosphide layers by high resolution x-ray diffraction and atomic force microscopy measurements. GaP layers are grown on misoriented and nominally exactly oriented silicon (001) substrates by metalorganic vapor phase epitaxy. Structural characterization is performed by reciprocal lattice map and transverse scan measurements of (00l)-reflections (l = 2, 4, 6). Transverse scan line profiles of GaP layers on exactly oriented and misoriented substrates are compared thoroughly and antiphase disorder related satellite peaks are observed on exactly oriented substrates. In addition, results imply that antiphase disorder is self-annihilated on misoriented substrates. The dependence of crystallographic tilt on growth temperature indicates structural coherence. Williamson-Hall-like plot of transverse scans reveals the lateral correlation length of crystalline defects of 79 nm which gives the average size of the mosaic crystallites. In addition, the mosaicity of the GaP layer is 0.042°.

Wurtzite-perovskite heterostructures composed of a high dielectric constant oxide and a wide bandgap semiconductor envision promising applications in field-effect transistors. In the present paper, the structural and electronic properties of LaAlO3/ZnO heterojunctions are investigated by first-principles calculations. We study the initial adsorption of La, Al, and oxygen atoms on ZnO (0001) and (000 1¯) surfaces and find that La atoms may occupy interstitial sites during the growth of stoichiometric ZnO (0001). The band gap of the stoichiometric ZnO (0001) surface is smaller than that of the stoichiometric ZnO (000 1¯) surface. The surface formation energy indicates that La or Al atoms may substitute Zn atoms at the nonstoichiometric ZnO (0001) surface. The atomic charges, electronic density of states, and band offsets are analyzed for the optimized LaAlO3/ZnO heterojunctions. There is a band gap for the LaAlO3/ZnO (000 1¯) heterostructures, and the largest variation in charge occurs at the surface or int...

Thermal conductivity (κ) is one of the fundamental properties of materials for phase change memory (PCM) application, as the set/reset processes strongly depend upon heat dissipation and transport. The κ of phase change materials in both amorphous and crystalline phases should be quite small, because it determines how energy-efficient the PCM device is during programming. At a high temperature, the electronic thermal conductivity (κe) is always notable for semiconductors, which is still lacking for antimony telluride under doping in the literature as far as we know. In this paper, using density functional theory and Boltzmann transport equations, we report calculations of lattice thermal conductivity κL and electronic thermal conductivity κe of the yttrium doped antimony telluride. We show that the average value of thermal conductivity decreases from ∼2.5 W m−1 K−1 for Sb2Te3 to ∼1.5 W m−1 K−1 for Y0.167Sb1.833Te3. This can be attributed to the reduced κL and κe, especially the κe at high temperature (nea...

Si-based single-electron tunneling (SET) devices have of late become an important alternative to the metal-based ones, both for ultralarge scale integration (ULSI) electronics and for electrical metrology. We have very recently been designing, fabricating, and measuring SET turnstiles, pumps, and charge-coupled devices using tunable barriers in silicon. Having shown the potential of these devices, we wish to understand the error mechanisms which may manifest themselves, and to predict the level of these errors, in order to decide how feasible these devices will be. In this paper, we devote a substantial amount of analysis to the consideration of the “dynamical” error mechanism. This particular error considers how electrons split up as the barrier is raised, or alternatively how the Coulomb blockade is formed. We then consider a wide variety of other errors, including thermal, frequency, leakage, and heating errors. We show the dependence of the error rate on each of those mechanisms, and predict maxima or...

The presence of ions in a liquid crystal (LC) influences the transmission characteristics of LC displays. These ions follow the electric field perpendicular to the electrodes and move back and forth under the influence of the ac field. Because of their charge, they can distort the electric field, which leads to transmission changes. Recently it was discovered that due to the LC anisotropy, ion motion parallel with the plane of the electrodes (perpendicular to the electric field) is also possible, even without lateral fields. After driving a pixel for a long time, the ions will accumulate at one pixel edge, which leads to unwanted image artifacts. In this paper, we investigate the frequency dependence of the lateral ion transport in twisted nematic liquid crystal displays at high and low ion concentrations, different ion mobilities, and LC rotational viscosities, for a fixed voltage just above the LC threshold.

In this paper, a phenomenon of polarization introduced by shock waves is experimentally studied. Although this phenomenon has been reported previously in the community of physics, this is the first time to link it to flexoelectricity, the coupling between electric polarization and strain gradients in dielectrics. As the shock waves propagate in a dielectric material, electric polarization is thought to be induced by the strain gradient at the shock front. First, we control the first-order hydrogen gas gun to impact and generate shock waves in unpolarized bulk barium titanate (BT) samples. Then, a high-precision oscilloscope is used to measure the voltage generated by the flexoelectric effect. Based on experimental results, strain elastic wave theory, and flexoelectric theory, a longitudinal flexoelectric coefficient of the bulk BT sample is calculated to be μ 11 = 17.33 × 10 − 6 C/m, which is in accord with the published transverse flexoelectric coefficient. This method effectively suppresses the majority...

Al2O3 is a potential dielectric material for metal-oxide-semiconductor (MOS) devices. Al2O3 films deposited on semiconductors usually exhibit amorphous due to lattice mismatch. Compared to two-dimensional graphene, MoS2 is a typical semiconductor, therefore, it has more extensive application. The amorphous-Al2O3/MoS2 (a-Al2O3/MoS2) interface has attracted people's attention because of its unique properties. In this paper, the interface behaviors of a-Al2O3/MoS2 under non-strain and biaxial strain are investigated by first principles calculations based on density functional theory (DFT). First of all, the generation process of a-Al2O3 sample is described, which is calculated by molecular dynamics and geometric optimization. Then, we introduce the band alignment method, and calculate band offset of a-Al2O3/MoS2 interface. It is found that the valence band offset (VBO) and conduction band offset (CBO) change with the number of MoS2 layers. The dependence of leakage current on the band offset is also illustrated. At last, the band structure of monolayer MoS2 under biaxial strain is discussed. The biaxial strain is set in the range from -6% to 6% with the interval of 2%. Impact of the biaxial strain on the band alignment is investigated.

In this paper, we have successfully grown the high-quality ScNiBi single crystals by a Bi flux method and investigated their electronic-transport properties. It was found that the ScNiBi single crystal is a gapless semiconductor with positive linear magnetoresistance (MR). Moreover, the field-dependent MR in the low-field region has demonstrated obvious weak antilocalization (WAL) effect below 50 K. The extremely large prefactor α and angle-dependent magnetoconductance ΔGxx suggest that the WAL effect originates from the contribution of a strong bulk spin-orbital coupling.

This paper presents an investigation of the mechanical response of a finite-thickness superconducting strip containing an elliptical cavity in oblique magnetic fields. After the Bean critical state model and the minimum magnetic energy variation procedure are employed, the dependency of the magnetic and mechanical properties on the aspect ratio of the strip and the tilt angles of the applied field and elliptical cavity is discussed. The results show that for a strip in an oblique magnetic field, the current front penetrates non-monotonically from the surface inwards in the initial stage. The magnetization of the strip and the applied field are not collinear, and the angle between them becomes smaller with increasing field. Simultaneously, the strip suffers from a torque produced by the electromagnetic force and then has a tendency to rotate. Compared with the defect-free case, the appearance of the elliptical cavity affects the magnetic property of the strip and further causes significant stress concentra...

In this paper, we briefly described how to use the vector or biaxial vibrating sample magnetometer (VSM) to determine the angular dispersion of easy axis in a magnetically soft film. For each angle of rotation φ of the external field H, a pair of the Mx-hysteresis and My-hysteresis loops could be obtained. Then, we changed the φ setting from negative to positive, with φ=0° indicating the exact direction of the hard axis of the film. Note, the easy axis has been induced by a deposition field h during fabrication of the film. From the characteristics of the Mx-hysteresis and My-hysteresis loops, the condition |φ| φc defines the “off-center zone.” The types of switching modes for the in-center and off-center zones, respectively, are different. Only the hysteresis behaviors in the latter zone are understood well for detailed explanations. Then, the normalized change ΔMy/MS due to the wall motions at the switching field |H|=HSW can be used to indicate t...

A recent paper by Mahan on energy‐gap narrowing in extrinsic semiconductors is compared and contrasted with a previous analysis by Inkson. It is found that, contrary to a statement by Mahan, the two papers rely on the same physical basis but use different means of calculation. The source of confusion is identified as the use of an inconsistent terminology.

In this paper we report a detailed study of photoreflectance (PR) in δ-Si:GaAs superlattices. PR spectra yield three contributions: (1) from intrinsic GaAs; (2) Franz–Keldysh oscillations (FKO) due to the surface electric field, whose value is explained by a simple capacitor model; and (3) FKO attributed to the buffer/superlattice interface. We observed the photovoltaic effect due to the probe beam in the PR arrangement and achieved surface voltage reductions up to 30%. We also present a time-resolved PR technique, which allows us to discriminate these contributions in the time domain and gives us the PR characteristic decay times.

In this paper, a theoretical study of N-polar GaN/AlxGa1-xN/GaN heterostructures is conducted systematically. The dependence of two-dimensional hole gas (2DHG, at the bottom AlxGa1-xN/GaN interface) and electron gas (2DEG, at the upper GaN/AlxGa1-xN interface) sheet densities on variables, such as GaN top layer thickness, AlxGa1-xN back barrier thickness, and Al content, is investigated. The effect of n-type doping in AlxGa1-xN and δ-doping concentrations in the GaN buffer on 2DHG and 2DEG sheet densities is also presented. For the unintentionally doped structure, the 2DHG-induced electric field E2DHG provides the only driving force in the 2DEG formation. Thus, in order to get high dense of 2DEG in such heterostructure, 2DEG and 2DHG shall coexist through proper AlxGa1-xN back barrier design. While for intentionally doped structure (with the n-type doped AlxGa1-xN back barrier layer or δ-doped GaN buffer layer), ionized donor-induced electric field Edonor is another driving force for 2DEG. The obtained in...

Light confinement induced by resonant states in aperiodic photonic structures are interesting for many applications. A particular case of these resonances can be found in 2D quasi-crystalline arrangements of dielectric cylinders. These systems present a rather isotropic band gap as well as isolated in-gap photonic states (as a result of spatially localized resonances). These states are built by high symmetry polygonal clusters that can be regarded as photonic molecules. In this paper we study the transmission properties of a slab of glass cylinders arranged in approximants of decagonal quasi-crystalline structure. In particular, we investigate the influence of the slab width in the transmission contrast between the states and the gap. The study is both experimental and numerical in the microwave regime. We find that the best transmission contrast is found for a width of around 3 times the radiation wavelength. The transmission at the band gap region is mediated by the resonances of the photonic molecules. If the samples are thin enough they become transparent except around a resonance of the photonic molecule which reflects the incoming light. In this case the behavior is reminiscent of an absorbing molecule.

In this paper, the multilayered structure composed of periodic arrays of graphene ribbons separated by the dielectric slabs is investigated for both the transverse electric (TE) and transverse magnetic (TM) polarizations. The transmission spectra show a stopband region between the low-THz frequency passband region and the higher-frequency one for TM polarization due to dual capacitive-inductive nature of the surface impedance corresponding to arrays of graphene ribbons. For TE polarization, the surface impedance is pure inductive; therefore, a passband region can be seen after the low-THz frequency stopband region. The in-plane permittivities are calculated based on the scattering parameters retrieval method. The negative permittivities are obtained in stopband regions corresponding to Bloch evanescent modes. This structure allows the propagation of backward waves in negative permittivity regime for TM polarization.

In this paper we report on the time behavior of the apparent pitch of a cholesteric mixture undergoing a step‐like dc electric field applied parallel to the helical axis. We show that the relative variation of the apparent pitch Δλ(t)/λ0 decreases from the initial value to negative ones (λ

Zn3N2 has been reported to have high electron mobility even in polycrystalline films. The high mobility in polycrystalline films is a striking feature as compared with group-III nitrides. However, the origins of the high mobility have not been elucidated to date. In this paper, we discuss the reason for high mobility in Zn3N2. We grew epitaxial and polycrystalline films of Zn3N2. Electron effective mass (m*) was determined optically and found to decrease with a decrease in electron density. Using a nonparabolic conduction band model, the m* at the bottom of the conduction band was derived to be (0.08 ± 0.03)m0 (m0 denotes the free electron mass), which is comparable to that in InN. Optically determined intra-grain mobility (μopt) in the polycrystalline films was higher than 110 cm2 V−1 s−1, resulting from the small m*. The Hall mobility (μH) in the polycrystalline films was significantly smaller than μopt, indicating that electron transport is impeded by scattering at the grain boundaries. Nevertheless, μH higher than 70 cm2 V−1 s−1 was achievable owing to the beneficial effect of the high μopt. As for the epitaxial films, we revealed that electron transport is hardly affected by grain boundary scattering and is governed solely by ionized impurity scattering. The findings in this study suggest that Zn3N2 is a high-mobility semiconductor with small effective mass.

We present a comprehensive analysis of surface plasmonpolaritondispersioncharacteristics associated with isotropic and anisotropic two-dimensional atomically thin layered materials (2D sheets) coupled to h-BN heterostructures. A scattering matrix based approach is presented to compute the electromagnetic fields and related dispersioncharacteristics of stacked layered systems composed of anisotropic 2D sheets and uniaxial bulk materials. We analyze specifically the surface plasmonpolariton (SPP) dispersioncharacteristics in case of isolated and coupled two-dimensional layers with isotropic and anisotropic conductivities. An analysis based on residue theorem is utilized to identify optimum optical parameters (surface conductivity) and geometrical parameters (separation between layers) to maximize the SPP field at a given position. The effect of type and degree of anisotropy on the shapes of iso-frequency curves and propagation characteristics is discussed in detail. The analysis presented in this paper gives an insight to identify optimum setup to enhance the SPP field at a given position and in a given direction on the surface of two-dimensional materials.

In the never-ending quest for higher areal recording density, perpendicular recording is viewed as the most likely candidate to supplant longitudinal recording. However, currently perpendicular recording is lagging longitudinal recording in terms of areal density by almost a factor of two. It is generally believed that the lack of optimized perpendicular head and media is hindering the progress of perpendicular recording in spite of its theoretical advantages. Recently, so-called oxide perpendicular media have become available. In such media, the perpendicularly oriented magnetic grains are physically isolated, e.g., in a SiO/sub 2/ phase, thus ensuring magnetic decoupling between the grains. This paper compares the recording performance of conventional and oxide perpendicular media, showing that the latter hold the promise of bridging the gap to longitudinal recording.

Recent articles have been published claiming that the ambipolar diffusion coefficient of semiconductors, Da, is basically independent of the excess‐carrier concentration, thus contradicting the conventional result of, for example, Fletcher. However, only a few experimentally verified papers on this subject are published. In the present work, a detailed experimental analysis of the ambipolar diffusion coefficient is presented regarding both temperature and injection‐level dependence. The ambipolar diffusion coefficient was measured in the low‐doped n base of a p‐i‐n type diode at different excess‐carrier concentrations and temperatures using an open‐circuit carrier decay (OCCD) method based on the free‐carrier absorption (FCA) technique. This investigation was performed in the carrier‐concentration range of 1015–2×1017 cm−3 and in the temperature range of 300–420 K, respectively. The ambipolar diffusion coefficient is experimentally found to behave in reasonable agreement with Fletcher’s theory, thus decre...

The measurement of quantum‐size behavior in semiconductor crystals has been examined through an analysis of the size dependence of the semiconductor’s absorption edge. In past studies, there appeared to be little agreement between theory and experiment for very small crystals. In this paper, the effects of crystal‐size distribution and tunneling of the carrier wave functions into the quantum well barrier are considered. An analysis of the microstructure size and absorption edge of CdTe clusters in a glass matrix is conducted with samples ranging from 0.16 to 0.8 times the exciton Bohr diameter at the Γ point and from 1 to 5 times the exciton Bohr diameter at the L point. Results show fully coupled exciton behavior at the L point and a more complex process at the Γ point. In the latter, the band‐gap energy increase with decreasing cluster size is significantly smaller than that calculated using a model in which the photoexcited carriers are assumed to be confined to a monosize set of clusters bounded by an...

This paper presents a review on the latest state of the novel bulk devices, with an emphasis on lenses for electron beams. As one application of high critical‐temperature (Tc) bulk superconductors, the author proposed the lenses (Supertrons) and his group has developed them. The principle of the lenses is simple: When one injects electron beams into narrow superconducting tubes, the tubes confine the self‐magnetic field of the beams to the bore of the tubes because of the Meissner effect. The enhanced field accordingly focuses the beams into thinner ones. The first two sections outline high‐Tc superconducting materials and fundamental characteristics of electron beams. In the body of this article, the lenses are evaluated according to the focusing of intense electron beams (∼340 keV, ∼1 kA, ∼10 ns) and assigned a figure of merit. Lenses were made from powder‐pressed yttrium‐ (Tc=∼90 K), bismuth‐ (∼105 K), thallium‐ (∼120 K), and melt‐processed yttrium‐based superconductors. From the experimental results, ...