Current-voltage characteristics of poly(diphenylenephthalide) thin films

Charge transfer near the threshold of polymer film transition (induced by a low uniaxial pressure) to the high-conductivity state is studied in an attempt to tackle the question of how the energy band structure of a wide-gap organic insulator varies near this threshold. The I-V characteristics of poly(diphenylenephthalide) films of various thickness versus uniaxial pressure are analyzed. The results obtained are treated within the model of space-charge-limited injection currents. The parameters of the injection model, such as the equilibrium concentration of electrons, electron mobility, the occupation of traps, etc., are estimated. It is concluded that deep traps due to an excess charge may appear in the energy gap of the polymer near the imref. This probably causes a narrow subband to arise, and charge transfer via this subband increases the charge carrier mobility and, hence, conductivity.     

Study of radially excited D_s(2~1S_0) and D_s(3P )

The unobserved J~P= 0~-radial excitation D_s(2~1S_0) is anticipated to have mass 2650 Me V(denoted as D_s(2650)). Study of hadronic production is an important way to identify highly excited states. We study hadronic production of D_s(2650) from higher excited resonances in a3P0 model. Relevant hadronic partial decay widths are found to be very small, which implies it is difficult to observe D_s(2650) in hadronic decays of higher excited resonances. Hadronic decay widths of radially excited D_s(3P) have also been estimated. The total decay widths of four D_s(3P) are large, but the branching ratios in the D_s(2650)η channel are very small, which implies that it seems impossible to observe D_s(2650) in hadronic decays of D_s(3P). The dominant decay channels of the four D_s(3P) have been pointed out, and D_1(2420), D_1(2430), D*2(2460), D(2550), D(2600),(1~1D_2)D(2750) and D_3*(2760) are possible to observe in hadronic production from D_s(3P).     

Emission tomography of radially symmetric objects and exponential Abelian transform

The properties of the exponential Abelian transform (EAT), which is defined as the exponential Radon transform (ERT) of a radially symmetric object just as the Abelian transform is the Radon transform of a radially symmetric object, are considered. A new approach to deriving the inverse EAT directly from the inverse ERT is suggested. The problems of numerical implementation of the EAT are discussed, including the problem of loss of information from deep-seated regions of the object, which is nonexistent in the case of the conventional Abel transform. The results obtained may be useful for reconstructing the spatial distribution of axisymmetric or spherically symmetric radiation sources.     

Recombination-induced voltage-dependent photocurrent collection loss in CdTe thin film solar cell

Recently, the efficiency of CdTe thin film solar cell has been improved by using new type of window layer Mg_xZn_1-xO (MZO). However, it is hard to achieve such a high efficiency as expected. In this report a comparative study is carried out between the MZO/CdTe and CdS/CdTe solar cells to investigate the factors affecting the device performance of MZO/CdTe solar cells. The efficiency loss quantified by voltage-dependent photocurrent collection efficiency (η_C(V')) is 3.89% for MZO/CdTe and 1.53% for CdS/CdTe solar cells. The higher efficiency loss for the MZO/CdTe solar cell is induced by more severe carrier recombination at the MZO/CdTe p—n junction interface and in CdTe bulk region than that for the CdS/CdTe solar cell. Activation energy (E_a) of the reverse saturation current of the MZO/CdTe and CdS/CdTe solar cells are found to be 1.08 eV and 1.36 eV, respectively. These values indicate that for the CdS/CdTe solar cell the carrier recombination is dominated by bulk Shockley—Read—Hall (SRH) recombination and for the MZO/CdTe solar cell the carrier recombination is dominated by the p—n junction interface recombination. It is found that the tunneling-enhanced interface recombination is also involved in carrier recombination in the MZO/CdTe solar cell. This work demonstrates the poor device performance of the MZO/CdTe solar cell is induced by more severe interface and bulk recombination than that of the CdS/CdTe solar cell.     

离轴径向偏振光束及其传输特性

基于Wolf近轴传输理论, 导出离轴径向偏振光束光强的解析表达式, 并研究离轴量对离轴径向偏振光束传输中光强分布的影响, 同时根据一阶矩质心位置的定义推导出离轴径向偏振光束的质心坐标, 研究其质心位置的变化规律. 结果表明, 与径向偏振光束不同, 离轴径向偏振光束在近场处传输时光强分布不均匀, 随着传输距离的增加, 光强分布均匀性逐渐得到改善, 而径向偏振光束在传输中始终保持空心对称光斑. 离轴量较小时, 近场处光强分布呈非对称空心面包圈形, 随着传输距离增达到一定程度, 光强分布演化为对称空心面包圈形, 离轴量越小, 演变距离越短; 离轴量较大时, 随着光束的传输离轴径向偏振光束的空心部分消失, 逐渐由空心面包圈形向高斯型演变, 径向偏振光束特性消失. 另一方面, 离轴径向偏振光束的质心不随传输距离的改变而改变. 质心纵坐标恒为零, 质心横坐标与光斑尺寸及离轴量相关. 随着光斑尺寸增大, 质心横坐标成线性增长. 当离轴量较小时, 质心横坐标随离轴量的增大呈非线性增长, 增长量不明显; 离轴量较大时, 质心横坐标随离轴量的增大呈线性增长, 且变化明显.     

Current-voltage characteristics simulation and analysis of 4H-SiC metal-semiconductor-metal ultraviolet photodetectors

The current-voltage (I-V) characteristics of 4H-SiC metal-semiconductor-metal (MSM) ultraviolet pho-todetector with different finger widths and spacings, different carrier concentrations and thicknesses of n-type epitaxial layer are simulated. The simulation results indicate that the dark current and the pho-tocurrent both increase when the finger width increases. But the effect of finger width on the dark current is more significant. On the other hand, the effect of finger spacing on the photocurrent is more significant. When the finger spacing increases, the photocurrent decreases and the dark current is almost changeless. In addition, it is found that the smaller the carrier concentration of n-type epitaxial layer is, the smaller the dark current and the larger the photocurrent wiU be. It is also found that I-V characteristics of MSM detector also depend on the epitaxial layer thickness. The dark current of detector is smaller and the photocurrent is larger when the epitaxial layer thickness is about 3 μm.     

The glueball G(1440) and radially excited pseudoscalar states

It is pointed out that there exist two isoscalar 0^?+ states near 1.4 GeV besides the axial-vector E(1420), one is a glueball and the other is a member of the radially excited pseudoscalar nonet. The relationship between the (2 ¹S₀)- and (1 ³P₁)- trajectories is discussed.     

Transient photocurrent and charge-transfer excitation bands in a tin-phthalocyanine (SnPc) polycrystalline film

Received: 27 December 1996/Accepted: 23 June 1997     

Current-voltage characteristics of a reflex discharge with a hollow cathode and self-heating electrode

Results are presented from experimental studies of the current-voltage characteristics of a reflex discharge with a self-heating electrode used in a source of atomic hydrogen. The processes occurring in a discharge cell and governing the main features of the characteristics obtained are investigated theoretically. An explanation of the general features of the discharge is proposed. It is shown that an abrupt decrease in the discharge voltage with increasing hydrogen flow rate is associated with penetration of the plasma into the hollow cathode and the ignition of a hollow cathode discharge. It is demonstrated that, as the discharge current increases, the glow discharge gradually transforms into an arc discharge with a heated cathode.     

Transient short-circuit photocurrent in ferroelectric semiconductor Sn2P2S6 films

Transient short-circuit photocurrents in films of the ferroelectric semiconductor Sn₂P₂S₆ are studied in a temperature range that includes the phase transition point. The influence of an external electric field and white-light illumination on the photoelectric response of samples is discussed.     

Propagation of electromagnetic waves in a waveguide with a radially symmetric height irregularity of the upper wall

We study the influence of a gradual (in the wavelength scale), radially symmetric height perturbation of a planar waveguide on the field of a vertical electrical dipole placed in the waveguide. We found an analytical expression for the Hertz potential for the dipole and observation point located on the uncurved wall. Radiophysical Research Institute, Nizhny Novgorod, Russia Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 6, pp. 530–535, June, 2000.     

Current-voltage characteristics of quasi-one-dimensional superconductors: an S-shaped curve in the constant voltage regime

Applying a constant voltage to superconducting nanowires we find that its I-V characteristic exhibits an unusual S behavior. This behavior is the direct consequence of the dynamics of the superconducting condensate and of the existence of two different critical currents: j(c2) at which the pure superconducting state becomes unstable and j(c1)相似文献   

Fabrication and optical properties of self-assembled InAsSb/InP nanostructures on InP (001) substrate

This article presents a study on the growth and optical properties of self-assembled InAsSb/InP nanostructures on (001) InP substrate, which are potential candidate materials for making mid-infrared lasers. The surfactant effect of Sb atoms is found to play a crucial role in the formation of flat InAsSb quantum dashes with almost identical island width no matter the change of InAsSb deposition thickness. The critical thickness for the transition from two-dimensional plane growth to three-dimensional island growth is observed to be less than two monolayer. And the photoluminescence measurements on InAsSb quantum dashes with different nominal Sb composition well demonstrate the band-gap bowing effect induced by the incorporation of Sb atoms into InAs quantum dots. The photoluminescence linewidth of InAsSb quantum dashes also present unusual temperature behavior, which can be attributed to the narrow size distribution of InAsSb quantum dashes.     

Influences of polarization effect and p-region doping concentration on the photocurrent response of solar-blind p–i–n avalanche photodiodes

The influences of polarization and p-region doping concentration on the photocurrent response of Al0.4Ga0.6N/Al0.4Ga0.6N/Al0.65Ga0.35N p–i–n avalanche photodetector are studied in a wide range of reverse bias voltages.The simulation results indicate that the photocurrent under high inverse bias voltage decreases with the increase of polarization effect,but increases rapidly with the increase of effective doping concentration in p-type region.These phenomena are analyzed based on the calculations of the intensity and distribution of the electric field.A high p-region doping concentration in the p–i–n avalanche photodetector is shown to be important for the efficient compensation for the detrimental polarization-induced electrostatic field.     

Current-voltage characteristics of SIS structures with localized states in the material of the barrier layer

Elastic resonant tunneling through a single localized state in an insulating layer (I-layer) situated in the constriction zone between two thick superconducting electrodes is investigated theoretically, and the current-voltage characteristic (IVC) of the structure is calculated. The accompanying analysis leads to the prediction that an appreciable current can flow through the structure, not at |eV|=2Δ (Δ is the modulus of the order parameter of the superconducting electrodes) as in the case of an ordinary SIS junction, but at |eV|⩾Δ, and also that the IVC can acquire segments of negative differential resistance in the case of tunneling through a single localized state. Averaging of the IVC over an ensemble of localized states distributed uniformly throughout the volume of the I-layer and with respect to the energy near the chemical potential min the limit Γ₀/Δ≫1 (Γ₀ is the half-width of the resonance line of the localized state) produces a smaller excess current than in a junction of the SNS type. It is shown that the IVC’s exhibit a transition from an excess current to a deficit current as Γ₀ decreases in the high-voltage range. Zh. éksp. Teor. Fiz. 114, 687–699 (August 1998)     

Optical and electrical characteristics of (LiCl) x (P2O5)1 − x glass

Homogeneous (LiCl) _x (P₂O₅)_1 − x glasses were synthesised using a melt-quenching method for x = 0.1–0.6 in the interval of 0.05. The amorphous structure of the samples was evident by the X-ray diffraction spectrum. The short range structures of the binary phosphate samples were examined by Fourier transform infrared spectroscopy, whilst the density of the samples was measured as supportive data for the investigations. The results of refractive indices as measured using an ellipsometer reveal the homogeneity of samples and was found to depend on the glass composition. The electrical properties of the glasses were investigated by ac impedance spectroscopy from 10 mHz to 1 MHz for temperatures ranging from room temperature to 573 K. An estimation of the bulk resistivity was obtained by taking the intercepts on the real axis at low frequencies of the complex impedance plot. The dc conductivities derived from the reciprocal of resistivity values were found to obey the Arrhenius relationship, and its activation energy shows a decreasing trend with the increase in LiCl content in the glass. Lastly, an equivalent circuits consisting of real and complex capacitors is proposed to describe the dielectric response of the glass.     

O(3) symmetric merons in an SU(3) Yang-Mills theory

We investigate irreducible, O(3) symmetric multiple-meron solutions to the classical SU(3) Yang-Mills equations in four-dimensional Euclidean space. The solutions have topological charge density equal to a sum of delta-functions with integer coefficients, and correspond to solutions of a system of two coupled singular elliptic equations. We prove the existence of twomeron solutions of the coupled system.Supported in part by the National Science Foundation under Grant No. PHY77-18762.     

O(2) symmetric connections in an SU(2) Yang-Mills theory

The general O(2) symmetric Yang-Mills equations are derived. An ansatz for O(2) symmetric merons is presented and it is shown that any connection in this ansatz will have SU(2) topological charge density which is a sum of delta functions at points in a plane with weights ± 1/2. It is shown that any connection in this ansatz will beC away from these points.National Science Foundation Pre-doctoral FellowSupported in part by the National Science Foundation under Grant PHY 77-18762     

Computer simulation of non-cooled long-wavelength multi-junction (Cd,Hg)Te photodiodes

A numerical analysis of long-wavelength multi-junction photodiodes constructed from Cd_xHg_1−xTe heterostructures is performed. The standard Newton iterative scheme is applied to solve the non-linear system of continuity equations and the Poisson equation. All quantities are expressed as a function of electric potential and quasi-Fermi levels. Results of computations are presented in the form of maps and plots illustrating spatial distributions of electrical potential and responsivity. Such an illustration enables us to explain the effect of reverse sign of the photovoltage occurring in photoelectric devices being manufactured.