Seebeck Enhancement Through Miniband Conductionin III–V Semiconductor Superlattices at Low Temperatures

We present theoretically that the cross-plane Seebeck coefficient of InGaAs/InGaAlAs III?CV semiconductor superlattices can be significantly enhanced through miniband transport at low temperatures. The miniband dispersion curves are calculated by self-consistently solving the Schr?dinger equation with the periodic potential, and the Poisson equation taking into account the charge transfer between the two layers. Boltzmann transport in the relaxation-time approximation is used to calculate the thermoelectric transport properties in the cross-plane direction based on the modified density of states and group velocity. It is found that the cross-plane Seebeck coefficient can be enhanced more than 60% over the bulk values at an equivalent doping level at 80?K when the Fermi level is aligned at an edge of the minibands. Other thermoelectric transport properties are also calculated and discussed to further enhance the thermoelectric power factor.     

Electrical Conductivity of Parylene F at High Temperature

The electrical conductivity of both as-deposited and annealed poly(α,α,α′,α′-tetrafluoro-p-xylylene) (PA-F) films has been investigated up to 400°C. The static conductivity (σ _DC) values of PA-F measured between 200°C and 340°C appear to be ∼2.5 orders of magnitude lower for annealed films than for as-deposited ones. This change is attributed to a strong increase in the crystallinity of the material occurring above 340°C. After annealing at 400°C in N₂, the σ _DC value measured at 300°C, for instance, decreased from 3.8 × 10⁻¹² Ω⁻¹ cm⁻¹ to 7.5 × 10⁻¹⁵ Ω⁻¹ cm⁻¹. Physical interpretations of such an improvement are offered.     

Effective Bi–Sb Crystals for Thermoelectric Cooling at Temperatures of T ≲ 180 K

Semiconductors - Extrusion methods have become widespread in the fabrication technology of thermoelectric materials with high strength characteristics. The extrusion method of thermoelectric...     

Mixed-Alkali Effect in Li2O–Na2O–K2O–B2O3 Glasses: Infrared and Optical Absorption Studies

The mixed-alkali effect (MAE) has been investigated in the glass system (40 ? x)Li₂O–xNa₂O–10K₂O–50B₂O₃ (0 mol% ≤ x ≤ 40 mol%) through density, modulated differential scanning calorimetry (DSC), and optical absorption studies. From the absorption studies, the values of the optical band gap (E _opt) for direct transition and Urbach energy (ΔE) have been evaluated. The values of E _opt and ΔE show nonlinear behavior with the compositional parameter. The density and glass-transition temperature of the present glasses also show nonlinear variation, supporting the existence of MAE. The infrared (IR) spectra of the glasses reveal the presence of three- and four-coordinated boron atoms. The specific vibrations of Li–O, Na–O, and K–O bonds were observed in the present IR study.     

Aging characteristics of ZnO–V2O5-based varistors for surge protection reliability

The effect of sintering temperature on clamping characteristics and pulse aging behavior of V₂O₅/MnO₂/Nb₂O₅ co-doped zinc oxide varistors was systematically investigated at 875–950 °C. Experimental results related to varistor effect showed that the breakdown field decreased dramatically from 6830 to 968 V/cm with the increase in the sintering temperature and the non-ohmic coefficient exhibited a maximum (49.5) at 900 °C in the sintering temperature. Varistors sintered at 900 °C exhibited the best clamp characteristics for the pulse current of 1–100 A, with the clamp voltage ratio of K = 1.86–2.77. Varistors sintered at 875 °C exhibited the strongest stability; variation rates for the breakdown field, for the non-ohmic coefficient, and for the leakage current density were −14.2%, −63.6%, and 59.0%, respectively, after application of a multi-pulse current of 100 A.     

Structural and dielectric properties of ZrO2–TiO2–V2O5 nanocomposite prepared by CO-precipitation calcination method

Nanocrystalline ZrO₂–V₂O₅–TiO₂ composite was synthesized by co-precipitation method and calcined at 500 and 700 °C. The formation of the composite material has been confirmed by X-ray diffraction analysis. The surface morphology was determined by SEM and HRTEM and it was seen that increase in calcination temperature increases the grain size. EDX analysis confirms the presence of zirconium, titanium and vanadium in the lattice. Optical absorption studies reveal a very low absorption in the visible region for both the samples. The dielectric constant, loss and ac conductivity of the pelletized samples have been examined at different temperatures as functions of frequency and the activation energies were calculated. The results indicated that the dielectric constant increases with calcination temperature. It was seen that the dielectric constant increases on the addition of Vanadia to zirconia–titania composite making it ideal for use as a gate dielectric material.     

Electrical properties of Au–Sb/p-GaSe:Gd Schottky barrier diode

Experimental results of the fabricated Schottky barrier diode on a GaSe:Gd substrate are presented. The electrical analysis of Au–Sb/p-GaSe:Gd structure has been investigated by means of current–voltage (I–V) and capacitance–voltage (C–V) measurements at 296 K temperature. The diode ideality factor and the barrier height have been obtained to be 1.07 and 0.85 eV, respectively, by applying a thermionic emission theory. At high currents in the forward direction, the series resistance effect has been observed. The series resistance has been determined from I–V measurements using Cheung's method.     

TeO2-Nb2O5-ZnO-CeO2玻璃非线性光学特性的研究

碲酸盐玻璃具有较高的二阶、三阶非线性极化率、高折射率、宽红外透过范围、低熔点温度和高介电常数等特性，因此被认为是光学和通讯系统中一种理想的材料，在非线性光学器件方面有很好的应用前景．比如，它具有较高的三阶光学非线性系数，因而被广泛应用于超快全光学开关器件．最近，一些重金属氧化物和稀土金属氧化物掺杂在碲酸盐玻璃     

Effect of Nonlinearity of the Phonon Spectrum on the Thermal Conductivity of Nanostructured Materials Based on Bi–Sb–Te

A theoretical investigation of the lattice thermal conductivity of nanostructured materials based on Bi–Sb–Te is presented. The calculations were based on relaxation time approximation and took into account both the real phonon spectra, obtained from first-principles by use of density functional theory, and the anisotropy of phonon relaxation time. Phonon relaxation time data were determined from experimental values of the lattice thermal conductivity. The decrease of the thermal conductivity caused by the nanostructure was compared with results from calculations based on the linear Debye approach. Estimation showed that phonon boundary scattering can lead to a 55% decrease of thermal conductivity for a grain size of ~20 nm in the Debye approximation. Taking the nonlinearity of the acoustic phonon spectrum into account leads to a 20% larger decrease of the thermal conductivity because of boundary scattering. The reason is that consideration of the real phonon spectrum increases the relative contribution to thermal conductivity of acoustic phonons with low frequencies that are scattered more strongly at nanograin boundaries. Similarly, estimation of lattice thermal conductivity reduction as a result of phonon scattering by nanoinclusions gave an 8% larger decrease when the real phonon spectrum was used rather than the linear Debye approximation. For such a substantial decrease of lattice thermal conductivity, the effect of the optical phonons was estimated; it was shown that optical phonons can reduce the change of thermal conductivity as a result of grain boundary scattering by no more than 10%. Finally, the minimum lattice thermal conductivity was estimated to be 0.07 W/m K because of acoustic modes (0.09 W/m K in the Debye approach) and 0.14 W/m K when the contribution of optical modes was also taken into consideration.     

Doped Ta2O5 and mixed HfO2–Ta2O5 films for dynamic memories applications at the nanoscale

The doping of Ta₂O₅ films with a proper element or its mixing with another high-k dielectric as a breakthrough to extend the potential of Ta₂O₅ toward meeting the criteria for future technological nodes is discussed. Essential issues in the engineering of storage capacitor parameters for dynamic memories based on Ti-doped Ta₂O₅, Hf-doped Ta₂O₅ and mixed HfO₂–Ta₂O₅ layers are presented. The benefits and the disadvantages of these modified Ta₂O₅ stacks are discussed.     

Physical and Electrical Properties of Dy2O3 and Dy2TiO5 Metal Oxide–High-κ Oxide–Silicon-Type Nonvolatile Memory Devices

In this paper, we compare the physical and electrical properties of metal oxide–high-κ oxide–silicon (MOHOS)-type devices using Dy₂O₃ and Dy₂TiO₅ films as charge-trapping layers. X-ray diffraction and x-ray photoelectron spectroscopy revealed the structural and compositional features of these films after annealing at various temperatures. MOHOS memory devices incorporating the Dy₂TiO₅ trapping layer that had been annealed at 800°C exhibited a larger memory window of ~2.91 V (measured at a sweep voltage range of ±9 V), higher flatband voltage shift of 2 V (programming voltage at 9 V for 0.1 s), and smaller charge loss of ~10% (measured at room temperature after 10⁴ s), relative to those of the systems that had been subjected to other annealing conditions. This result suggests that the Dy₂TiO₅ film featuring a higher dielectric constant as well as a thinner silicate layer provides a higher probability of charge carrier trapping and deeper electron trapping levels. In addition, the centroid of trapped charge in the Dy₂TiO₅ layer was extracted by the constant current stress method and compared with that of the Dy₂O₃ layer.     

Effect of annealing and electrochemical properties of sol–gel dip coated nanocrystalline V2O5 thin films

Nanocrystalline vanadium pentoxide (V₂O₅) thin films were deposited on glass substrates by a simple and cost effective sol–gel dip coating method. The effect of annealing on microstructure and optical properties of V₂O₅ thin films were investigated. Formation of nanorods with the average diameter of 500–750 nm after annealing is observed by scanning electron microscopy. X-ray diffractometry indicates that an orthorhombic structured thin film is transformed to β-V₂O₅ nanorods by subsequent annealing at 500 °C. It was also confirmed that the growth of nanorods strongly correlates with annealing conditions; nanorod formation can be explained by surface diffusion phenomenon. The electrochemical performance of the V₂O₅ nanorods was investigated by cyclic voltammetry.     

Characteristics of DC Electrical Conductivity and Optoelectronic Features of Tin Dioxide Nanocrystals Synthesized by Sol–Gel Chemistry

Semiconductors - Nanostructured tin dioxide powders were synthesized successfully through a sol–gel route. Subsequent thermal treatment was carried out at different temperatures to obtain the...     

Characteristics of ZnOV2O5MnO2Nb2O5Er2O3 semiconducting varistors with sintering processing

The effects of sintering temperature on the microstructure, electrical properties, and dielectric characteristics of ZnOV₂O₅MnO₂Nb₂O₅Er₂O₃ semiconducting varistors have been studied. With increase in sintering temperature the average grain size increased (4.5–9.5 μm) and the density decreased (5.56–5.45 g/cm³). The breakdown field decreased with an increase in the sintering temperature (6214–982 V/cm). The samples sintered at 900 °C exhibited remarkably high nonlinear coefficient (50). The donor concentration increased with an increase in the sintering temperature (0.60×10¹⁸–1.04×10¹⁸ cm^?3) and the barrier height exhibited the maximum value (1.15 eV) at 900 °C. As the sintering temperature increased, the apparent dielectric constant increased by more than four-fold.     

Electrical and Photoelectric Properties of α-Si/SiO2 and α-Ge/SiO2 Multilayer Nanostructures on p-Si Substrates Annealed at Various Temperatures

Semiconductors - The properties of multilayer α-Si(Ge)/SiO2 nanostructures deposited onto p-Si substrates and annealed at various temperatures are investigated. The total nanolayer thickness...     

Room temperature highly selective ethanol sensing behavior of hydrothermally prepared Te–V2O5 nanorod nanocomposites

Tellurium–vanadium pentoxide (Te–V₂O₅) nanorod nanocomposites were synthesized via a facile hydrothermal route. It is found that the Te nanorods are dispersed among the V₂O₅ nanorods. Gas sensing measurements show that the heterostructured nanorods have a higher and more stable response with better selectivity towards ethanol as compared to ammonia and propylamine gases at room temperature, and they also possess the lower detection threshold and relatively shorter response time compared with that of pure V₂O₅ nanorods. This enhanced stable and selective sensing behavior is due to the unique character of the one-dimensional nanostructured geometry and a p–n junction of the composite, and it may be explained on the basis of energy band model.     

Ab Initio Calculations and Measurements of Thermoelectric Properties of V2O5 Films

Density functional theory and the Boltzmann transport equation were used to calculate the thermoelectric transport coefficients for bulk V₂O₅ and MV₂O₅ (M = Cr, Ti, Na, Li). The structural relaxation for the given compounds based on the ABINIT code was observed. The temperature dependences of the Seebeck coefficients as well as electrical and thermal electrical conductivities of all relaxed structures displayed anisotropic behavior. Electrooptical measurements of thermoelectric properties were carried out on V₂O₅ thin films obtained by thermal evaporation with different post-annealing treatments. A Seebeck coefficient of ?148 μV/K at T = 300 K was obtained in the in-plane direction for V₂O₅ thin films with thickness less than 100 nm.     

Electrical Conductivity and Dielectric Properties of Se85Te15−x Sb x (x = 0 at.%, 2 at.%, 4 at.%, and 6 at.%) Thin Films

The alternating-current (ac) conductivity and dielectric properties of Se₈₅Te_15?x Sb _x (x = 0 at.%, 2 at.%, 4 at.%, and 6 at.%) films are reported in this work. Thin films were deposited by thermal evaporation under base pressure of 10^?5 Torr. The films were well characterized by x-ray diffraction, differential scanning calorimetry, and energy-dispersive x-ray spectroscopy. The ac conductivity and dielectric properties have been investigated for the studied films in the temperature range from 297 K to 333 K and over the frequency range from 10² Hz to 10⁵ Hz. The experimental results indicate that the ac conductivity $ \sigma_{\rm{ac}} (\omega ) $ and the dielectric constant depend on temperature, frequency, and Sb content. The frequency dependence of $ \sigma_{\rm{ac}} (\omega ) $ was found to be linear with a slope lying very close to unity and is independent of temperature. This behavior can be explained in terms of correlated barrier hopping between centers forming intimate valence-alternation pairs. The density of localized states N(E _F) at the Fermi level is estimated. The activation energy $ \Updelta E(\omega ) $ was found to decrease with increasing frequency. The dielectric constant ε ₁ and dielectric loss ε ₂ were found to decrease with increasing frequency and increased with increasing temperature over the ranges studied. The maximum barrier height W _m for the studied films was calculated from an analysis of the dielectric loss ε ₂ according to the Guintini equation. The values agree with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott for chalcogenide glasses. The variation of the studied properties with Sb content was also investigated.     

掺铒TeO2-B2O3-Nb2O5-ZnO玻璃系统的光谱性质和热稳定性的研究

制备了碲酸盐玻璃样品70TeO2-(15-x)B2O3-xNb2O5-15ZnO-1wt%Er2O3(TBN,x=0,3,6,9,12,15 mol%).测试了玻璃样品的热稳定性和光谱性质.根据Judd-Ofelt理论计算了TBN玻璃中Er3 离子的强度参数(Ω2=(5.42～6.76)×10-20 cm2,Ω4=(1.37～1.73)×10-20cm2,Ω6=(0.70～0.94)×10-20 cm2),发现随着Nb2O5含量的增加,Ωt(t=2,4,6)先增加后减小.研究表明Er-O键共价性主要受基质玻璃中非桥氧数的影响,而阴阳离子间电负性的影响可以忽略.应用McCumber理论计算了Er3 离子的受激发射截面(σe=(0.77～0.91)×10-20 cm2)和Er3 离子4I13/2→4I15/2发射谱的半高宽度(FWHM=65～73 nm).比较了不同基质玻璃中Er3 离子的荧光半高宽和受激发射截面.结果表明TBN玻璃系统具有较好的带宽性能,是一种制备宽带光纤放大器的潜在基质材料.