Temperature dependent transport properties of CuInSe2-ZnO heterostructure solar Cell

Experimental study of dc and ac transport properties of CuInSe₂/ZnO heterostructure is presented. The current-voltage (I-V) and frequency dependent capacitance (C-f) characteristics of CuInSe₂/ZnO heterostructure were investigated in the temperature range 160-393 K. The heterostructure showed non-ideal behavior of I-V characteristics with an ideality factor of 3.0 at room temperature. Temperature dependent dc conductivity studies exhibited Arrhenius type behavior and revealed the presence of trap level. The C⁻²-V plot measured at frequency 50 kHz had shown non-linear behavior. An increase in capacitance with temperature was observed. The capacitance-frequency characteristics exhibited a transition between low frequency and the high frequency capacitance. As the temperature was lowered the transition occurred at lower frequencies. The frequency and temperature dependent device capacitance had shown a defect state having activation energy of 108 meV.     

Effect of SrTiO3 thickness on the capacitance–voltage characteristics of (La,Sr)CoO3/(Pb,La)(Zr,Ti)O3/SrTiO3/LaVO3 epitaxial heterostructures

We report the effect of SrTiO₃ thickness on the capacitance?Cvoltage (C?CV) characteristics of (La,Sr)CoO₃/(Pb,La)(Zr,Ti)O₃/SrTiO₃/LaVO₃ metal?Cferroelectric?Cinsulator?Csemiconductor (MFIS) epitaxial heterostructures. The C?CV measurement of the heterostructure exhibited the asymmetry of capacitance with respect to gate bias. Within the given thickness range (5?C30 nm), the amount of capacitance reduction at positive gate bias and the rapidness of capacitance reduction decreased with increasing SrTiO₃ thickness, which is consistent with the C?CV characteristics of conventional silicon-based MFIS capacitors. These results suggest that quantitative understanding on the electrical behavior of oxide heterostructures is possible with C?CV analysis, with potentially important implications on their device applications.     

Preparation and characterization of polyaniline+TiO2 composite films

In this work, we have prepared electrochemically and studied a composite materials based on an organic conducting polymer, polyaniline (PANI), in which inorganic semiconductor titanium dioxide (TiO₂) particles were incorporated with different concentrations. The polyaniline/titanium dioxide composite material which had been deposited by cyclic voltammetry on substrates of indium tin oxide was then characterized. The cyclic voltammogram showed one redox couple characteristic of the oxidation and reduction states of the produced composite material. The impedance spectroscopy study showed that the resistance of the film increases with the TiO₂ cocntent incorporated in the polymer. The incorporation of TiO₂ in PANI covering the surfaces was confirmed by the scanning electron microscopy and the energy dispersive X-ray analysis. The morphological analysis of the film surfaces showed that the TiO₂ nanoparticle increased the roughness. These observations allow to consider a new approach to improve the physicochemical properties of the interface between the organic and inorganic material. The I–V characteristics of PANI+TiO₂ heterostructure diode showed the nonlinear nature of the I–V curve of PANI+TiO₂ heterostructure device.     

The DNA electronic specific heat at low temperature: The role of aperiodicity

The electronic specific heat spectra at constant volume (_CV$C_V$) of a long-range correlated extended ladder model, mimicking a DNA molecule, is theoretically analyzed for a stacked array of a double-stranded structure made up from the nucleotides guanine G, adenine A, cytosine C and thymine T  . The role of the aperiodicity on _CV$C_V$ is discussed, considering two different nucleotide arrangements with increasing disorder, namely the Fibonacci and the Rudin–Shapiro quasiperiodic structures. Comparisons are made for different values of the band fillings, considering also a finite segment of natural DNA, as part of the human chromosome Ch22.     

AlGaN/GaN异质结Ni/Au肖特基表面处理及退火研究

采用O₂等离子体及HF溶液对AlGaN/GaN异质结材料进行表面处理后，Ni/Au肖特基接触特性比未处理有了明显改善，反向泄漏电流减小3个数量级.对制备的肖特基接触进行200—600℃ 5min的N₂气氛退火，发现退火冷却后肖特基反向泄漏电流随退火温度增大进一步减小.N₂气中600℃退火后肖特基二极管C-V特性曲线在不同频率下一致性变好，这表明退火中Ni向材料表面扩散减小了表面陷阱密度；C-V特性曲线随退火温度增大向右移动，从二维电子气耗尽电压绝对值减小反映了肖特基势垒的提高. 关键词： AlGaN/GaN 肖特基接触 表面处理 退火     

Substrate effects on V2O3 thin films

We apply density functional theory and the augmented spherical wave method to analyze the electronic structure of V₂O₃ in the vicinity of an interface to Al₂O₃. The interface is modeled by a heterostructure setup of alternating vanadate and aluminate slabs. We focus on the possible modifications of the V₂O₃ electronic states in this geometry, induced by the presence of the aluminate layers. In particular, we find that the tendency of the V 3d states to localize is enhanced and may even cause a metal-insulator transition.     

The anomalous acoustoelectric current in single-electron transport devices with three pairs of shallow-etched gates

In order to study the influence of the modulation effect in systems of multiple etched gates, we design single-electron transport devices in an AlGaAs/GaAs heterostructure with three pairs of shallow-etched gates in series. In the experiment, the voltage applied to V_g1 is set in the pinched-off region; V_g2 is set in open region and V_g3 is swept from the pinched-off region to the open. Interestingly, the results indicate that the acoustoelectric current increases from zero to a maximum and then decreases to the zero again, a sharp peak is observed. Change of the electron reservoir's chemical potential is considered as the physical origin of this experimental phenomenon.     

Electrical and optical characteristics of porous silicon impregnated with LaF3 by a novel chemical bath technique

The structural, electrical and optical characteristics of porous silicon (PS) due to the impregnation of LaF₃ into PS by a novel chemical-bath deposition (CBD) technique have been investigated in this article. Without removing the PS from the anodization chamber the impregnation with LaF₃ has been done by reacting LaCl₃ with HF in the same chamber at room temperature. The impregnation of LaF₃ was confirmed by the SEM on the cross-section of the LaF₃/PS/Si system and EDX. The modification of PS surface by LaF₃ had direct influence on the electrical and optical properties of PS. Electrical properties of Ag/LaF₃/PS/p-Si/Ag structures were studied through the current-voltage (I-V) and capacitance-voltage (C-V) characteristics. Formation of metal-insulator-semiconductor (MIS) diode was evident whose forward current increased with annealing. A diode factor of about 2.4 has been obtained for the annealed heterostructure indicating a high density of trap states. The C⁻²-V curves of all samples showed negative flat band voltage of around −2 V confirming a large number of fixed positive charges in the LaF₃. The photoluminescence (PL) intensity of the LaF₃-impregnated PS showed aging for the as-deposited samples, but when annealed PS structure recovered the PL intensity. Experimental results show that the optimized chemical bath passivation process for the LaF₃ on porous silicon could enable the porous silicon to be an important material for photonic application.     

Asymptotic interaction between He,H, H2 and a graphite surface

An atom or molecule far from a surface experiences an interaction V ~ ?C₃z^?3, where z is the distance to the surface. We compute the coefficient C₃ for He, H, and H₂ interacting with a graphite surface. The calculation utilizes measured frequency dependent values of the polarizabilities and dielectric function. Comparison is made with C₃ values deduced from surface scattering and adsorption experiments.     

Electrical and dielectric properties of Al/HfO2/p-Si MOS device at high temperatures

The temperature dependence of capacitance–voltage (C–V) and conductance–voltage (G/w–V) characteristics of Al/HfO₂/p-Si metal-oxide-semiconductor (MOS) device has been investigated by considering the effect of series resistance (R_s) and interface state density (N_ss) over the temperature range of 300–400 K. The C–V and G/w–V characteristics confirm that the N_ss and R_s of the diode are important parameters that strongly influence the electric parameters in MOS device. It is found that in the presence of series resistance, the forward bias C–V plots exhibits a peak, and its position shifts towards lower voltages with increasing temperature. The density of N_ss, depending on the temperature, was determined from the (C–V) and (G/w–V) data using the Hill–Coleman Method. Also, the temperature dependence of dielectric properties at different fixed frequencies over the temperature range of 300–400 K was investigated. In addition, the electric modulus formalisms were employed to understand the relaxation mechanism of the Al/HfO₂/p-Si structure.     

C 2-Cofiniteness of 2-Cyclic Permutation Orbifold Models

In this article, we consider permutation orbifold models of C ₂-cofinite vertex operator algebras of CFT type. We show the C ₂-cofiniteness of the 2-cyclic permutation orbifold model ${(V \otimes V)^{S_2} }$ for an arbitrary C ₂-cofinite simple vertex operator algebra V of CFT type. We also give a proof of the C ₂-cofiniteness of a ${\mathbb{Z}_{2}}$ -orbifold model ${V_{L}^{+}}$ of the lattice vertex operator algebra V _L associated with a rank one positive definite even lattice L by using our result and the C ₂-cofiniteness of V _L .     

Structural and dielectric properties of La- and Ti-modified K0.5Na0.5NbO3 ceramics

We report the results of studies of rectifying behavior, positive magneoresistance (MR), the charge-transport mechanism and the effect of an electric field on a ZnO (n)/La_0.5Pr_0.2Sr_0.3MnO₃ (LPSMO) (p)/SrNb_0.002Ti_0.998O₃ (SNTO) (n) heterostructure comprising two p–n junctions fabricated using the pulsed laser deposition technique. The heterostructure exhibits rectifying behavior over a wide temperature and field range having hysteresis in I–V behavior (forward bias) due to the tunneling of charge carriers. It is also observed that, depending on the nature of the electric field bias to n-type ZnO and SNTO, the junction resistance becomes modified, which has been explained on the basis of spin injection in the heterostructure. The observation of unconventional positive MR at room temperature has been justified on the basis of interface effects and the reduction in barrier height obtained using fitting of the I–V data by a thermionic emission model.     

Electrical properties of metal-GaAs Schottky barriers

Schottky barrier contacts have been fabricated by vacuum evaporation of thin films of six different metals (Mg, In, Al, Au, Bi and Sb) onto chemically cleaned n-type GaAs substrates. Bi and Sb contacts on GaAs have been reported for the first time. The contacts were examined for their C-V and I-V characteristics. The diodes exhibit near ideal characteristics for all the metals with values of the ideality factor n ranging from 1.06 to 1.1. The values of the barrier height obtained from C-V measurements could be brought into agreement with those obtained from I-V measurements only when the ideality factor was also included in the expression of the saturation current. By employing the most recent and reliable values of metal work function φ_M, the dependence of barrier height on φ_M has been investigated and an estimate of the surface state density and the Fermi level at the GaAs surface has been made. The surface state density obtained from this analysis is significantly larger than that reported by previous workers.     

Rotational line strengths in the Lyman and Werner bands of H2

Rotational line strengths in the Lyman and Werner bands of molecular hydrogen are affected by the nonadiabatic interaction between the B and C states. Numerical results are presented for the effect of this interaction on relative rotational line strengths for V_x = 0 and V_B ≤ 25, V_c ≤ 9. The B-C interaction is shown to have a pronounced effect for many levels. This difference in rotational line strength factors from the usual Hönl-London factors should be taken into account when relating line oscillator strengths to band oscillator strengths. Relative rotational line strengths are also computed for transitions between C-state levels and excited vibrational levels in the X state. Comparison is made to the measured Werner band emission line intensities of Schmoranzer and Geiger [J. Chem. Phys., 59, 6153 (1973)].     

Remark on the status of non-conservation of parity in nuclear beta-decay

Equality of β-decay coupling constants C′_A/C_A = C′_V/C_V = 1, implying V - A interaction, is less verified than commonly assumed. Deducing limits 0.52 < C′_V/C_V < 1.93 and 0.82 < C′_A/C_A < 1.22 we discuss a possible V+A admixture with a mass ratio m(W^V?A)/m(W^V+A) < 0.56 for intermediate bosons W^V±A.     

Bias voltage dependence of inverted magnetoresistance on the annealing temperature in MgO-based magnetic tunnel junctions

MgO-based magnetic tunnel junctions (MTJs) with a layer sequence Ir₂₂Mn₇₈ or Fe₅₀Mn₅₀ (10 nm)/CoFe (2 nm)/Ru (0.85 nm)/CoFeB (0.5?t<2 nm)/MgO (2.5 nm)/CoFeB (3 nm) have been fabricated. The bias voltage dependence of tunneling magnetoresistance (TMR) is given as a function of the annealing temperature for these MTJs, which shows the TMR ratio changes its sign from inverted to normal at a critical bias voltage (V_C) when an unbalanced synthetic antiferromagnetic stack CoFe/Ru/CoFeB is used. V_Cs change with the thickness of the pinned CoFeB and annealing temperature, which implies one can achieve different V_Cs by artificial control. The asymmetric V_C values suggest that a strong density-of-states modification occurs at bottom oxide/ferromagnet interface.     

Negative capacitance of ZnGa2Se4/Si nano-heterojunction diode

The negative capacitance (NC) behavior in p-ZnGa₂Se₄/n-Si nano-crystalline HJD was characterized by admittance-voltage method. The C–V, G–V and R _s –V for the studied diode were analysed in the frequency range of 1–5 MHz and in the temperature range of 303–423 K. The capacitance and conductance plots were interpreted in terms of interface states and series resistance. The C–V and G/ω–V plots exhibit a pounced peak due to the interface states and the series resistance effects. The negative capacitance behavior in the studied diode can be explained in terms of the transient currents.     

Temperature derivatives at constant volume of the elastic constants of the alkali halides

Values of dC/dT)_V have been computed from experimental dC/dT)_P and dC/dP)_T for the three elastic constants (expressed as $\text{B}{}_{\mathrm{T}}\text{, C}{}_{44}\text{and}\text{(C}{}_{11}\text{?C}{}_{12}\text{)}\text{2)}$ of each of the 16 Li, Na, K, and Rb halides. The dC/dT)_V measure the explicit dependence of C on T, the effect of thermal expansion having been removed. The dC/dT)_V are all small (compared with dC/dT)_P), are all negative, and vary quite systematically and smoothly with anion, with cation and with the three elastic constants. Negative dB_T/dT)_V is accounted for both thermodynamically and by available lattice dynamical calculations. dC/dT)_V for shear constant is expressed in terms of two vibrational mode parameters, whose values can then be estimated from the observed value, and the trend of dC/dT)_V with Debye temperature.     

The effect of interface states, excess capacitance and series resistance in the Al/SiO2/p-Si Schottky diodes

The current-voltage (I-V) characteristics of Al/SiO₂/p-Si metal-insulator-semiconductor (MIS) Schottky diodes were measured at room temperature. In addition the capacitance-voltage (C-V) and conductance-voltage (G-V) measurements are studied at frequency range of 10 kHz-1 MHz. The higher value of ideality factor of 3.25 was attributed to the presence of an interfacial insulator layer between metal and semiconductor and the high density of interface states localized at Si/SiO₂ interface. The density of interface states (N_ss) distribution profile as a function of (E_ss − E_v) was extracted from the forward bias I-V measurements by taking into account the bias dependence of the effective barrier height (Φ_e) at room temperature for the Schottky diode on the order of ≅4 × 10¹³ eV⁻¹ cm⁻²_. These high values of N_ss were responsible for the non-ideal behaviour of I-V and C-V characteristics. Frequency dispersion in C-V and G-V can be interpreted only in terms of interface states. The N_ss can follow the ac signal especially at low frequencies and yield an excess capacitance. Experimental results show that the I-V, C-V and G-V characteristics of SD are affected not only in N_ss but also in series resistance (R_s), and the location of N_ss and R_s has a significant on electrical characteristics of Schottky diodes.     

“Crystal fields” for magnetic ions in metals from itinerant electrons

The interaction of conduction electrons with host ions are shown to give rise to “crystal fields”, V_C, which act on the magnetic ion in some dilute magnetic alloys. Crystal fields, V_N, arising directly from ions neighbouring the magnetic ion have been compared with V_C to show that the overall crystal field splitting from all 3d magnetic ions in axial symmetries is enhanced by the p-like character of V_C. A⁰₄〈r⁴〉 from V_N is also increased by the d-component of V_C. The angular properties of itinerant electron states give rise to the above results. For all rare-earth ions in fcc symmetry the radial and angular components of conduction-electron states with mainly d, but also f character, are shown to give rise to a reversal in sign of A⁰₄〈r⁴〉 from V_N. A⁰₆〈r⁶〉 is enhanced by the f component of the conduction electrons.