High-field conduction in some chalcogenide glasses

Current voltage (I–V) characteristics have been studied at various temperatures in amorphous thin films of Ge₂₂Se_78−xBi_x and Ge_xSe_80−xTe₂₀ where 0≤x≤10. At low electric fields, ohmic behaviour is observed. However, at high electric fields (E≡10⁴ V cm⁻¹) the current becomes superohmic. Analysis of the data shows the existence of space charge-limited current (SCLC) in a-Ge₂₂Se_78−x Bi_x in which In (IIV) vs V curves are found to be straight lines with decreasing slopes at high temperatures, in accordance with the theory of SCLC for a uniform distribution of traps. However, in the case of a-Ge_xSe_80−xTe₂₀, no SCLC is observed. Instead, in I vs V^1/2 curves are found to be straight lines with decreasing slopes at high temperatures. A more detailed analysis shows that the mechanism of conduction is of Poole–Frenkel type in this system. Copyright © 2000 John Wiley & Sons, Ltd.     

Non-Fourier thermal conduction in nano-scaled electronic structures

When very fast phenomena and small structure dimensions are involved, the classical law of Fourier becomes inaccurate. A more sophisticated model is then needed to describe the thermal conduction mechanisms in a physically acceptable way. In this paper the according diffusion equation is solved for a nano-scaled semiconductor substrate, in order to gain physical insight in the problem. Analytical solutions for the temperature and heat flux distributions are presented. The complex thermal impedance and thermal step response of the structure are discussed. The most remarkable fact is that the temperature inside the substrate can go below the ambient temperature for a short amount of time. The results also clearly demonstrate the wave character of the heat propagation and the analogy with RLC transmission lines. This work concerns a slightly extended version of a paper that was presented at the latest MIXDES Conference (Gdynia, Poland). It is submitted for the Special Issue MIXDES 2006 of the Analog Integrated Circuits and Signal Processing journal upon invitation of the MIXDES Scientific Committee.     

Near-edge conduction band electronic states in SiGe alloys

Spatially resolved electron energy loss spectroscopy (EELS) measurements in GeSi alloys illustrate the relationship of atomic structure to local electronic structure. Extending earlier measurements, where electronic structure was found to be controlled by composition in relaxed alloys, measurements in anisotropically strained alloys show splitting of normally degenerate band edges into two components. In a strained Si quantum well, this allows the engineered band offset to be followed from the GeSi substrate through the well to the alloy-capping layer. In the high-mobility conduction channel, the band edge is found to be very sharp, in spite of obvious composition roughness. Near a misfit dislocation under the Si well, the band edge can shift by as much as 0.25 eV due to local strain. Within the core of the defect, however, strictly local behavior dominates the observations. Local conduction band splitting and in-gap states are both observed.     

Effect of electronegative impurities on electronic conduction in compressed nitrogen

Measurements of pulsed electron currents in compressed nitrogen show that appreciable attachment occurs to oxygen impurity of the order of 10 parts per million, and that the process depends on the partial pressure of oxygen, as well as on the ratio of electric field and gas density, E/p.     

High-field transport in indium phosphide

Theoretical estimates of intervalley scattering rates in InP are used to determine velocity/field curves. The results do not support the 3-level model of high-field transport in this material.     

High-field superconductor technology

The past two years have seen the acceptance of superconducting magnets for engineering installations, the development of more advanced and robust engineering materials than the earlier conductors, and the wider application of high-field superconducting magnets in development programs for high-energy physics and thermonuclear fusion research. Their principal advantage is the great saving in operating cost when used in large-volume magnets up to 3 teslas. At higher fields a further advantage is their lower capital cost as compared with that of conventional electromagnets. They also have the potential, not as yet realized, of being more compact than a conventional electromagnet of identical performance.     

High-field distribution function in GaAs

Use of the drifted Maxwellian distribution is shown to be unjustified for GaAs samples in which the Gunn effect is usually observed, because the carrier concentration is much too low for electron-electron collisions to predominate. It is pointed out that solution of the Boltzmann equation is considerably simpler at fields high enough so that the average electron energy exceeds several times the optical phonon energy. The simplification occurs because the polar optical scattering may then be considered elastic. Relaxation times and rates of energy loss in acoustic, optical, and intervalley scattering are examined in order to determine which scattering processes must be included in the Boltzmann equation. It is found that intervalley scattering is very likely to be more important than polar optical scattering for high-energy electrons in either the central or the outer valleys. Approximate solutions of the Boltzmann equation for electrons in the lower valley are given for a wide range of fields. The number of electrons per unit energy range, calculated from the solution of the Boltzmann equation, is given for electrons in both valleys for a field of 2.4 × 10³volts/cm, where the approximation mentioned should be reasonably good.     

Simulation of electronic/ionic mixed conduction in solid ionic memory devices

The electronic/ionic mixed conduction is examined in solid ionic memory devices by numerically solving the Poisson-Nernst-Planck equations using the computational platform PROPHET. The boundary conditions for the Poisson-Nernst-Planck system are determined based on the theoretical treatments as a Dirichlet type. The chemical composition of the mixed conductor under the reference electrode and the magnitude of applied biases are considered as important parameters in the simulation. The results show that the deviation of carrier distribution increases from the analytical solutions with the increase of applied biases and the decrease of the partial pressure of the non-metallic component near the reference electrode in solid ionic memory devices.     

Single band electronic conduction in hafnium oxide prepared by atomic layer deposition

Current–voltage and capacitance–voltage measurements on MOS structures with hafnium gate oxide (HfO₂) prepared by atomic layer deposition were conducted to determine the dominant current conduction in the Al/HfO₂/Si structure. In n-type substrate MOS structures, electron injection from Al into HfO₂ is observed when the Al electrode is negatively biased. Whereas in p-type MOS capacitors at negative biasing, no hole injection can be detected and the current in the insulator is again due to the electron injection from Al. These results unambiguously indicate that in both p- and n-type substrates and at both biasing polarities only electronic current conduction in the Si/HfO₂/Al is significant.     

High-field electron velocity in silicon surface-accumulation layers

Temperature dependence of saturation velocity in bulk silicon and in surface-accumulation layers was studied between room temperature and 600 K. The saturation electron velocity in bulk silicon was found to have a steeper temperature dependence than previously reported. The saturation velocity in surface-accumulation layers was found to be equal to the electron velocity in the bulk, and independent of the perpendicular electric field     

Transient charging currents in insulators

It is shown that charging currents in good insulators can be used to distinguish between different empirical carrier injection laws, if most carriers are trapped according to the Walden model. Schottky injection and power law injection are considered in detail. The current falls as t⁻ⁿ, 0<n<1. For power law injection the isochronal current density j ∞ E_k, where E is the applied field, and it is shown that the apparent power k 1 for 0·6 < n < 0·9, whatever the true power law exponent p. This accords with the experimentally observed superposition theorem. Some limitations of the power law injection process proposed by Levine are discussed.     

High-field stressing of LPCVD gate oxides

We have investigated gate oxide degradation as a function of high-field constant current stress for two types of oxides, viz. standard dry and LPCVD oxides. Charge injection was done from both electrodes, the gate and the substrate. Our results indicate that compared to dry oxides, LPCVD oxides show reduced charge trapping and interface state generation for inversion stress. The degradation in LPCVD oxides with constant current stress has been explained by the hydrogen model     

用于高场科学的飞秒激光振荡器

超快激光振荡器已经成为科学技术中普遍存在的设备。然而,许多年以来,它们的脉冲能量一直被限制在纳焦范围内。应用高强度脉冲需要依赖复杂的放大器系统,但这些系统大都要在千赫兹量级的低重复频率下进行操作。近来．飞秒激光振荡器的脉冲能量有了极大的增加,一些实验已经可以在多重兆赫兹重复频率下进行。这为其在许多领域的应用开辟了一条有前途的新路。本文概述了高功率飞秒激光振荡器技术的当前发展状态,特别是锁模薄片激光器,并讨论了它们在多重兆赫兹重复频率条件下在驱动高场科学实验方面的潜在应用。     

High-field transport in InGaAs/InAlAs modulation-doped heterostructures

The velocity-field and mobility-field characteristics of normal and inverted InGaAs/InAlAs modulation-doped heterostructures grown by molecular-beam epitaxy have been measured at 300 and 77 K. Veloczities of 3.0 × 10⁷and 1.7 × 10⁷cm/s have been measured in the normal and inverted structures, respectively, at 77 K. Current instabilities are observed at the corresponding field values. Hall mobilities decrease With field beyond 500 V/cm, principally due to phonon scattering. The mobilities in normal and inverted heterostructures attain Similar values at fields higher than 1 kV/cm, irrespective of the low-field values.     

High-field effects in silicon nitride passivated GaN MODFETs

This paper presents a detailed study of high-field effects in GaN MODFETs. Degradation of DC characteristics and change of flicker noise due to hot electron and high-reverse current stresses in Si/sub 3/N/sub 4/ passivated GaN MODFETs have been investigated. The authors observe that during hot electron stress, electron trapping in the barrier layer and interface state creation occur. These cause a positive shift of V/sub t/, reduce I/sub D/, skew the transfer characteristics, and degrade g/sub m/. Flicker noise (1/f) measurements show that after hot electron stress, the scaled drain current noise spectrum (S/sub I(D)//I/sub D//sup 2/) decreases in depletion, but increases only slightly in strong accumulation, corroborating the creation of interface states but only a small creation of transition-layer tunnel traps that contribute to 1/f noise. During high-reverse current stress, electron trapping dominates for the first 50-60 s and then hole trapping and trap creation begin to manifest. However, there still is net electron trapping under the gate after one hour of stress. The degradation processes bring about a positive shift of V/sub t/, degrade I/sub D/ and g/sub m/, and increase reverse leakage. After high-reverse current stress, S/sub I(D)//I/sub D//sup 2/ increases substantially in strong accumulation, indicating the creation of transition layer tunnel traps.     

High-field transport with hot phonons in degenerate semiconductors

The effect of phonons in non-thermodynamic equilibrium (hot-phonons) on steady-state transport in degenerate bulk and two-dimensional (2D) semiconductor structures is studied. The phonon-drift effects are taken to be negligible, and, the formulation is confined to electrons in a single parabolic band interacting with a - population of polar-optic phonons, restricted to interface modes in the 2D case. Hot phonons in bulk semiconductors lead not only to a decrease in the energy relaxation rate, but, also, to a decrease in the mobility as the carrier concentration n_3D is increased. Hot phonons in 2D systems, on the other hand, cause the energy relaxation rate and mobility to go through a minima as the electron concentration n_2D is increased. The electron drift velocity, contrary to the bulk case, is seen to with n_2D for n_2D > 10¹² cm⁻², and reflects the difference in the nature of electron density of states in the two cases.     

Application of genetic algorithms for electronic devices placement in structures with heat conduction through the substrate

The paper presents an implementation of a genetic algorithm for electronic devices placement optimization. It is assumed that nine electronic devices can be positioned in any place on a substrate surface (in accordance to a grid). Because of that, a new, 2-level optimization algorithm has been created. Positions of nine electronic devices each dissipating different power are optimized in respect of thermal criteria and wiring length. This paper compares results obtained using simple algorithm having permutational coding with new 2-level algorithm.     

Theoretical studies of electronic conduction and optical generationmechanisms in the double-heterostructure optoelectronic switch (DOES)

The effects of other physical properties on the electrical and optical properties of the double-heterostructure optoelectronic switch device are calculated. The device is similar to an earlier version, but the charge sheet responsible for the unique electrical and optical switching properties of the device is placed in the wide-bandgap barrier layer rather than in the narrow-bandgap active layer. This generally improves the overall operating characteristics of the device because in principle it allows higher charge sheet doping values. This is possible because the charge sheet remains ionized even for very high inversion channel densities