Self-consistent equilibria in a cylindrical reversed-field pinch

Summary A previous investigation by one of us, concerning the self-consistent equilibria of a two-region (plasma+gas) cylindrical Tokamak, is extended to the similar equilibria of a Reversed-Field Pinch, where a significant current density is driven by a dynamo electric field due to turbulence. The previous model has been generalized under the following basic assumptions:a) to the lowest order, the turbulent dynamo electric fieldE ^t is expressed as a homogeneous function of degree 1 of the magnetic fieldB, sayE ^t =α·B, with α being a 2nd-rank tensor, homogeneous of degree 0 inB, and generally depending on the plasma state;b)E ^t does not appear in the plasma power balance, as if it were produced by a Maxwell demon able to extract the needed power from the plasma internal energy. In particular we show that, in the simplest case when both α and the plasma resistivity η are isotropic and constant, the magnetic field turns out force-free with constant abnormality αμ₀/η for vanishing axial electric fieldE _z . This case has also been solved analytically, for whateverE _z , under circular, besides cylindrical, symmetry.     

Analytic theory of electric field depinning in the one-dimensional Fukuyama-Lee-Rice hamiltonian

Using Feigel'man's method in the theory of one-dimensional random systems we have evaluated analytically the depinning electric fieldE _T and the static dielectric constant ₀ for the Fukuyama-Lee-Rice hamiltonian in the weak pinning limit and for low temperatures. This is accomplished by solving a Fokker-Planck equation for finitedc electric fields in order to determine the field dependent pinning energy. The dielectric constant is found to remain independent of the electric field up to the threshold. The product ₀ E _T is also evaluated and compared with other theories.     

Experimental analysis of current conduction through thermally grown SiO<Subscript>2</Subscript> on thick epitaxial 4H-SiC employing Poole-Frenkel mechanism

Electrical properties of SiO₂ grown on the Si-face of the epitaxial 4H-SiC substrate by wet thermal oxidation technique have been experimentally investigated in metal oxide-silicon carbide (MOSiC) structure with varying oxide thicknesses employing Poole-Frenkel (P-F) conduction mechanism. The quality of SiO₂ with increasing thickness in MOSiC structure has been analysed on the basis of variation in multiple oxide traps due to effective P-F conduction range. Validity of Poole-Frenkel conduction is established quantitatively employing electric field and the oxide thickness using forward I–V characteristics across MOSiC structures. From P-F conduction plot (ln(J/E) vs. E ^1/2), it is revealed that Poole-Frenkel conduction retains its validation after a fixed electric field range. The experimental methodology adopted is useful for the characterization of oxide films grown on 4H-SiC substrate.     

Electrical properties and memory effect in the field effect transistor based on organic ferroelectric insulator and pentacene

We have fabricated a field effect transistor (FET) based on an organic ferroelectric insulator and molecular conductor, and investigated the electrical properties and memory effects on the PEN-FET. We have observed a drastic change in the drain current at around the coercive electric fieldE _c of the organic ferroelectric insulator in not only a FET (PEN-FET) based on a pentacene (PEN) film but also a FET (IPEN-FET) based on an iodine doped PEN film. The magnitude of the change of the drain current for the IPEN-FET is 200 times larger than that for the PEN-FET. It is expected from these results that the PEN-FET (especially the IPEN-FET) is an improvement in such devices, since it operates at a low gate electric field accompanied by the appearance of the spontaneous polarization in the organic ferroelectric insulator. In addition, we have found that the drain current for the PEN-FET does not return to the initial drain current ofE _G =0 V/cm for more than one week, even if the gate electric field is changed to 0 V/cm from 500 V/cm(>E _c ). From these results, it is suggested that the PEN-FET becomes a memory device.     

Spontaneous transverse EMF in inelastic scattering of quasi-two-dimensional electrons

We calculate the spontaneous transverse electric fieldE _y which arises in a quasi-two-dimensional superlattice in a strong driving electric fieldE _x when the electron energy spectrum is nonadditive. The interaction of electrons with nonpolar optic phonons is taken into account. The stability of nonzero values ofE _y is determined from examination of the minimum in the synergy potential. The temperature dependence of the critical fieldE _xc (the bifurcation point) is determined, and the voltage—current curves are determined. State Pedagogical University, Volgograd. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 99–102, July, 1997.     

A method to separate conservative and magnetically-induced electric fields in calculations for MRI and MRS in electrically-small samples

This work presents a method to separately analyze the conservative electric fields (E_c, primarily originating with the scalar electric potential in the coil winding), and the magnetically-induced electric fields (E_i, caused by the time-varying magnetic field B1) within samples that are much smaller than one wavelength at the frequency of interest. The method consists of first using a numerical simulation method to calculate the total electric field (E_t) and conduction currents (J), then calculating E_i based on J, and finally calculating E_c by subtracting E_i from E_t. The method was applied to calculate electric fields for a small cylindrical sample in a solenoid at 600 MHz. When a non-conductive sample was modeled, calculated values of E_i and E_c were at least in rough agreement with very simple analytical approximations. When the sample was given dielectric and/or conductive properties, E_c was seen to decrease, but still remained much larger than E_i. When a recently-published approach to reduce heating by placing a passive conductor in the shape of a slotted cylinder between the coil and sample was modeled, reduced E_c and improved B1 homogeneity within the sample resulted, in agreement with the published results.     

Equal-permittivity states induced in a ferroelectric

Conditions under which a ferroelectric subjected to an electric field acquires equal-permittivity paraelectric states at different temperatures are studied. The temperature dependences of the control (inducing) field intensity and feasible permittivity interval (ɛ_min-ɛ_max) are obtained. The effect of intersection of the ɛ(E, T _i ) characteristics of the ferroelectric in the paraelectric state is analyzed. With the control field and temperature varying consistently, the permittivity ɛ_i of strontium titanate films and films of the barium titanate-strontium titanate solid solution may be kept constant in a wide (200–320 K) temperature range and, at the same time, changed by more than twofold by varying the electric field.     

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.     

Ferroelectric properties of a nonequilibrium electron gas

We show that a quasi-two-dimensional electron gas in a strong, attracting electric fieldE _x acquires ferroelectric properties. At certain temperatures, a transverse electric fieldE _y can arise spontaneously via a nonequilibrium phase transition. The Curie temperature is determined by|E _x |. Volgogradskii State Teachers University, Platan Scientific Research Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 72–79, April, 1998.     

Analysis of A-DLTS spectra of MOS structures with thin NAOS SiO2 layers

A set of MOS structures with thin SiO₂ layers prepared by nitric acid oxidation (NAOS) method was investigated using acoustic deep level transient spectroscopy (A-DLTS) to explain the role of annealing treatment (post-oxidation annealing (POA) and post-metallization annealing (PMA)) at different conditions on the distribution of interface states. The activation energies of interface states and the corresponding capture cross-section were calculated both from Arrhenius plots constructed for individual peaks of the A-DLTS spectra and applying the method of modeling of measured acoustic spectra. The energy distribution of the interface states was determined also from the dependence of acoustoelectric response signal (ARS) on the external bias voltage (U _ac - V _G curves). By comparing the A-DLTS spectra, U _ac - V _G characteristics and some electrical measurements (G-V, I-V curves) of investigated MOS structures with no treatment with those treated with POA and/or PMA, the role of individual treatments was observed. The definite decrease of the interface states in the structures with the PMA treatment in comparison with the POA treatment was confirmed too.     

2D-Electron Heating in Electric and Magnetic Crossed Fields

2D-electron heating in a potential well of a single n-(AlAs) _x (GaAs)_1–x /i-GaAs (x = 0.28) heterojunction is studied for the cases of a classical (weak) magnetic field B and constant and pulsed electric fields at fixed temperatures 77 and 4.2 K. It is shown that the heating of two-dimensional electrons is similar to that of the bulk ones. The magnetic field cools electrons, and this is manifested in the shifts of the characteristic critical electric fields E _{c 1} and E _{c 2} and in the regions of nonlinearity of voltage-current characteristics. The dependence of the effective electron temperature on the electric field T _e(E)_B is determined.     

控制氧化层对双势垒纳米硅浮栅存储结构性能的影响

在等离子体增强化学气相沉积(PECVD)系统中,利用逐层淀积非晶硅(a-Si)和等离子体氧化相结合的方法制备二氧化硅(SiO₂)介质层.电容电压(C-V)和电导电压(G-V)测量结果表明：利用该方法在低温(250 ℃)条件下制备的SiO₂介质层均匀致密,其固定氧化物电荷和界面态密度分别为9×10¹¹cm^-2和2×10¹¹cm^-2·eV^-1,击穿场强达4.6 MV/cm,与热氧化形成的SiO₂介质层的性质相当.将该SiO₂介质层作为控制氧化层应用在双势垒纳米硅(nc-Si)浮栅存储结构中,通过调节控制氧化层的厚度,有效阻止栅电极与nc-Si之间的电荷交换,延长存储时间,使存储性能得到明显改善. 关键词： 等离子体氧化 二氧化硅 纳米硅 控制氧化层     

On the stationary state of plasma in a magnetostatic and a potential field I

An analysis is made in the guiding centre approximation of the stationary state of a collisionless plasma in an inhomogeneous magnetostatic field in the presence of an electric fieldE ₀=–V and some additional field acting on the longitudinal motion of electrons and ions by the effective potentialsW _e andW _i The following are derived in particular: 1) the distribution functions of the quasi-neutral plasma with Maxwellian distribution of the longitudinal velocities; 2) the stationary perturbations of arbitrary distribution function caused by changing the effective potentials byW _e,i; 3) formulae describing the concentration in some cases with an incomplete Maxwellian distribution.The author is greatly indebted to the participants of the Colloquium held at the Institute of Plasma Physics, Czechoslovak Academy of Sciences, on March 15, 1966, for their criticism of his results.     

Time Dependence of the Capacitance of a MOS Silicon Tunnel Diode under the Influence of Hydrogen

The results of theoretical and experimental investigations into the time dependence of the capacitance of MOS silicon diodes with a thin tunnel dielectric and a palladium field electrode under the influence of a gas hydrogen-containing mixture are presented. Analytical expressions are derived that describe the time dependence of the capacitance of the space charge region (SCR) of the MOS tunnel diode operating in depletion and enrichment regimes. It is demonstrated that the time dependence of the SCR capacitance of the MOS diode placed in the gas mixture is caused by diffusion of hydrogen atoms from the field electrode to the SiO _x –n-Si interface. The relaxation time of hydrogen atom accumulation at the interface is 47 s for the diode with a SiO _x layer thickness of 3.7 nm placed in the gas mixture with 0.3 vol.% of H₂. It has been established that the flat band voltage and the SCR capacitance of the MOS diode change under the influence of the gas mixture due to the decreased density of surface acceptor states at the SiO _x –n-Si interface, the increased positive charge density in the dielectric, and the decreased contact potential difference.     

Partition function zeros for the one-dimensional ordered plasma in Dirichlet boundary conditions

We consider the grand canonical partition function for the ordered one-dimensional, two-component plasma at fugacity in an applied electric fieldE with Dirichlet boundary conditions. The system has a phase transition from a low-coupling phase with equally spaced particles to a high-coupling phase with particles clustered into dipolar pairs. An exact expression for the partition function is developed. In zero applied field the zeros in the plane occupy the imaginary axis from –i to –i_c and i_c to i for some _c. They also occupy the diamond shape of four straight lines from ±i_c to _c and from ±i_c to –_c. The fugacity acts like a temperature or coupling variable. The symmetry-breaking field is the applied electric fieldE. A finite-size scaling representation for the partition in scaled coupling and scaled electric field is developed. It has standard mean field form. When the scaled coupling is real, the zeros in the scaled field lie on the imaginary axis and pinch the real scaled field axis as the scaled coupling increases. The scaled partition function considered as a function of two complex variables, scaled coupling and scaled field, has zeros on a two-dimensional surface in a domain of four real variables. A numerical discussion of some of the properties of this surface is presented.     

Direct indication of lateral nonuniformities of MOS capacitors from the negative equivalent interface trap density based on charge-temperature technique

The charge-temperature technique was used to investigate the oxide properties of silicon MOS capacitors fabricated on a wafer with an oxide thickness of 660 Å. The stretchout of high frequencyC — V curve of the capacitor after a positive charge-temperature aging was proved to be due to the lateral nonuniformities of mobile charges and the increase of interface traps. The effect of lateral nonuniformitites was found to be successfully described by a model consisting of two parallelly connected nonuniform capacitors. The only parameter of importance is their area ratio, which can be easily determined by theoretical fitting. The appearance of a negative equivalent interface trap density was proposed as a new method to directly identify the existence of lateral nonuniformities.     

渐变带隙氢化非晶硅锗薄膜太阳能电池的优化设计

利用一维微电子-光电子结构分析软件(AMPS-1D)在AM1.5G(100 mW/cm2)、室温条件下模拟和比较了有、无渐变带隙氢化非晶硅锗(a-SiGe:H)薄膜太阳能电池的各项性能.计算结果表明:渐变带隙结构电池具有较高的开路电压(V oc)和较好的填充因子(FF),转换效率(E ff)比非渐变带隙电池提高了0.477%.研究了氢化非晶硅(a-Si:H)、氢化非晶碳化硅(a-SiC:H)和氢化纳米晶硅(nc-Si:H)三种不同材料的窗口层对a-SiGe:H薄膜太阳能电池性能的影响.结果显示:在以nc-Si:H为窗口层的电池能带中,费米能级E F已经进入价带,使得窗口层电导率及电池开路电压有所提高,又由于ITO与p-nc-Si:H的接触势垒较低,使得接触处的电场降低,更有利于载流子的收集.另一方面,窗口层与a-SiGe:H薄膜之间存在较大的带隙差,在p/i界面由于能带补偿作用形成了价带势垒(带阶)?E v,阻碍了空穴的迁移,因此我们在p/i界面引入缓冲层,使得能带补偿作用得到释放,更有利于空穴的迁移和收集,得到优化后单结渐变带隙a-SiGe:H薄膜结构太阳能电池的转换效率达到了9.104%.     

Solar cell materials and their basic parameters

Parameters such as the energy gapE _g , open circuit voltageV _oc , short circuit current densityj _sc , fill factor F.F., efficiency η, antireflection coating condition A.R. and illumination conditions of currently known photovoltaic diodes are reviewed and tabulated, followed by some critical comments.     

Theoretical Study of the Structure of the Electric Field in Helical Toroidal Plasmas

A set of transport equations is analyzed, including the bifurcation of the electric field. The structure of the electric field is studied by use of the theoretical model for the anomalous transport diffusivities. A steep gradient of the radial electric field (E _r) is obtained at the electric domain, where the electric domain is the structure of the electric field in which the ambipolar E _r spatially changes from the electron root (E _r>0) to the ion root (E _r<0). The suppression of the anomalous transport diffusivity is studied in the presence of a strong shear of the electric field. The hard transition between the multiple ambipolar solutions in the structure of the radial electric field is examined. The details of the structure of the electric domain interface are investigated.     

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.