Current transport in bistable granular structures

Electrical breakdown in GaAs Schottky diodes creates a granular filamentary structure of submicron dimensions between the contacts. The filament exhibits very fast (<2 nsec) electrical switching between stable resistance states. Irrespective of the contact metal, the filament becomes superconducting when in the low-resistance state. Electron transport in all the resistance states is intergrain tunneling between metallic inclusions and is governed by an activation energy. Switching is not based on metal transport.     

Spontaneous switching in cavityless optically bistable systems

Relaxation cavityless optical bistability is studied when a semiconductor is exposed to light quanta with an energy exceeding the transition energy and the free-electron relaxation time depends on temperature. The numerical analysis of dynamic equations for temperature and free-electron density demonstrates that 11 regimes of light-semiconductor interaction are possible. The regimes are classified in terms of the features of temperature-intensity characteristic curves, namely, by the number and arrangement of instability and quasistability segments and by the presence or absence of bistability. It is found that both the upper and the lower branch of a bistable characteristic curve may be unstable, which results in spontaneous switchings between the respective states. Similarly, if the upper state is unstable and the lower state is stable, a small perturbation of the parameters (free-electron temperature and density) near the former causes the transition to the oscillatory regime. If the upper state is unstable and a small perturbation of the lower (stable) state excites a damped oscillation, spontaneous switchings result if the fluctuating temperature exceeds some critical value for the lower state.     

Long switching times in absorptive bistable systems

We study the switching characteristics of a Fabry-Pérot cavity containing a saturable absorber and driven by an external laser. It is shown how long switching times can arise in such a system and an expression is given for the switching time.     

The structures and stabilities of mixed inert gas cluster ions: NeHe+ n and ArHe+ n

DIM-type matrices for RgHe⁺ _n clusters have been established from the results of ab initio calculations on RgHe and RgHe⁺ (Rg = Ne and Ar). The method has been tested against ab initio calculations on linear and T shaped RgHe⁺ ₂ and found to be satisfactory. Rotational invariance has been established for larger clusters, and the geometries and energies of clusters up to n = 16 have been determined. Ne cluster ions are more stable than Ar cluster ions because of the greater contribution from charge transfer, and are structurally different. The relative stabilities of these cluster ions are consistent with the available experimental data.     

Optical switching between bistable soliton states: a theoretical review

In this paper we summarize what is currently known about optical switching between bright bistable soliton states in one and higher dimensions. A guideline to selecting media with appropriate intensity-dependent refractive indices to support bistable solitary waves is presented. The stability criterion for robustness of the solitary waves is discussed. Finally, some methods and numerical examples of optical switching are presented.     

Dynamics of optical and electrooptical switching in photo-thermal bistable CdS crystals

We investigate the dynamical properties of photo-thermal Self Electrooptic Effect Devices (SEEDs) fabricated of thin single crystal platelets in a wide region of excitation intensities at room temperature. Detailed characteristics of the switching processes and dynamics are precented for optical and for the first time for electro-optical types of bistable operation using an improved contact geometry. The role of the substrate of the SEED is also taken into account. It is shown that in the case of rectangular excitation pulses of light or of voltage the switching process can be divided into two regions, namely the crystal reaction time and the switching time itself. Both depend sensitively on the applied optical or electrical pulse height and also on the initial preheating. Critical slowing down is observed in the optical and the electrical case.Experimental results are discussed in terms of the thermal reaction of the crystal and of the substrate. The frequency dependencies of the switching processes are given. A quantitative theoretical analysis based on the heat conduction equation is done. Simple analytical formulas are deduced and discussed together with the experimental data.     

All-optical transistor action with bistable switching in a photonic crystal cross-waveguide geometry

We demonstrate all-optical switching action in a nonlinear photonic crystal cross-waveguide geometry with instantaneous Kerr nonlinearity, in which the transmission of a signal can be reversibly switched on and off by a control input. Our geometry accomplishes both spatial and spectral separation between the signal and the control in the nonlinear regime. The device occupies a small footprint of a few micrometers squared and requires only a few milliwatts of power at a 10-Gbit/s switching rate by use of Kerr nonlinearity in AlGaAs below half the electronic bandgap. We also show that the switching dynamics, as revealed by both coupled-mode theory and finite-difference time domain simulations, exhibits collective behavior that can be exploited to generate high-contrast logic levels and all-optical memory.     

Heavily doped Si:P emitters of crystalline Si solar cells: recombination due to phosphorus precipitation

The measured saturation current density J_0e of heavily phosphorus‐doped emitters of crystalline Si solar cells is analysed by means of sophisticated numerical device modelling. It is concluded that Shockley–Read–Hall (SRH) recombination exceeds Auger recombination significantly; it is caused by inactive phosphorus. This explains the large discrepancies between measured and simulated J_0e values, observed persist‐ently over the last two decades in industrially fabricated Si solar cells. As a consequence, the heavily phosphorus‐diffused emitters still bear a significant potential to contribute to higher Si solar cell efficiency levels, if the amount of inactive phosphorus can be reduced. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Dynamic magnetization reversal and bistable states in antiferromagnetic multilayer structures

The dynamic behavior of the magnetization under a transverse microwave field is investigated in a system of magnetic layers with cubic crystallographic anisotropy coupled through interlayer antiferromagnetic exchange interaction. An orientational phase transition is found to occur as the microwave field frequency and amplitude are varied. It is established that there is a frequency range in which several steady-state regimes of precession of magnetic moments exist. The limits of this range can be efficiently controlled both by varying the strength of the bias magnetic field and the amplitude of the microwave field.     

Influence of two-photon absorption on bistable switching in a silicon photonic crystal microcavity

By employing a simplified nonlinear coupled mode theory, we discuss the influence of two-photon absorption (TPA) on the characteristics of bistable switching. It is revealed that the critical value of frequency detuning for bistability rises linearly with increasing TPA coefficient k (when k is less than 30), and eventually access to a saturated value. It is also found that TPA effect will be enhanced for a greater frequency detuning, especially when transmission reaches its peak value. As a result, the peak transmission will decrease monotonously with the increasing frequency detuning. Based on this simplified model, the TPA-induced temperature rise in microcavity is also estimated. The theoretical predictions show good agreement with the simultaneous results, as well as the proposed experimental phenomena.     

Phase switching and quantum interference in a 3-level Λ-shape bistable model

The steady state bistable behaviour of a three-level Λ-shape is examined in the presence of a control field $({\rm \Omega} +\chi \left( t\right) e^{i\varphi})$({\rm \Omega} +\chi \left( t\right) e^{i\varphi}) : Ω is the strong Rabi component, $\chi \left( t\right) $\chi \left( t\right) is the stochastic part with relative phase ϕ; with quantum interference between decay channels taken into account. One- and two-way phase switching effect for the transmitted field against the phase are predicted at fixed values for the incident input field. Also cooperative switching effect shows multistable/bistable behaviour. Quantum interference tends to diminish the dispersive effects responsible for multistable behaviour (in the input-output relation and the cooperative switching diagram) and asymmetry (in the phase switching diagram). Equivalence of the role of the stochastic part of the control field with that of the “classically” squeezed field is shown to occur only in the absence of quantum interference.     

Resonant tunneling transistor lasers: A new approach to obtain multi-state switching and bistable operation

Bipolar resonant tunneling heterotransistor structures, which can be configured to operate as multi-state or as bistable lasers, are described. Both edge and surface-emitting structures are presented. Computations of various optoelectronics parameters including confinement factor, threshold current density, and cavity modes for a stripe-geometry structure are presented. In addition, simulations of base and collector currents are given for a resonant tunneling transistor to demonstrate the feasibility of lasing in the base region.     

Electron-phonon coupling in highly doped n type silicon

The effect of free electrons on the optical phonon of silicon at the center of the Brillouin zone is studied using the Raman scattering technique. Heavy doping gives rise to a continuous electronic Raman scattering and makes the phonon line shape assymetric. The profile factor which is related to the disymetry, is shown to have the signes of the matrix elements of the electron-phonon interaction.     

Current filamentation in bistable semiconductor systems with two global constraints

The recent advent of integral circuits combining bistable semiconductor structures with a spatially distributed driving gate has opened up new possibilities for development of self-organizing active media with controllable properties which are of potential interest for neural computer technology. In the present paper the theoretical study of instabilities and current filamentation in such systems is advanced. The consideration is based on a generalized model which treats a gate driven bistable system as an extended active medium with two global constraints related to the main and gate circuits, respectively. It is shown that the presence of a spatially distributed controlling subsystem — a driving gate — leads to a new effect of transversal nonlocal coupling between system elements which acts dramatically upon the system behaviour. The results obtained in a general form regardless of the concrete semiconductor structure design are illustrated by the example of a gate-driven pnpn-structure.     

Dynamics of spatial structures in arrays of nonlocally coupled bistable units

We present the results of investigation of a dynamical system consisting of nonlocally coupled bistable units. The dynamics of spatial structures in an array with a gradually increasing coupling coefficient is studied. The formation of spatial structures in the case of strong nonlocal coupling between units is examined. This work was presented at the Summer Workshop “Dynamic Days” (Nizhny Novgorod, June 30–July 2, 1998). Volga State Academy of Water Transport, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 12, pp. 1581–1585, December, 1998.     

Spin Hall effect in doped semiconductor structures

In this Letter we present a microscopic theory of the extrinsic spin Hall effect based on the diagrammatic perturbation theory. Side-jump and skew-scattering contributions are explicitly taken into account to calculate the spin Hall conductivity, and we show that their effects scale as sigma(xy)SJ/sigma(xy)SS approximately (h/tau)/epsilonF, with tau being the transport relaxation time. Motivated by recent experimental work we apply our theory to n- and p-doped 3D and 2D GaAs structures, obtaining sigma(s)/sigma(c) approximately 10(-3)-10(-4), where sigma(s(c)) is the spin Hall (charge) conductivity, which is in reasonable agreement with the recent experimental results of Kato et al. [Science 306, 1910 (2004)] in n-doped 3D GaAs system.