Low-temperature Impurity Breakdown Research Articles

Non-ohmic hopping conduction of a diode base extracted from the diode current-voltage characteristics

Using the method of extracting a series resistance from a p- n diode current-voltage characteristics developed earlier, parameters of low-temperature non-ohmic conduction in bases of two types of silicon diodes have been studied. In the diode of the first type, with finite value of impurity ionization energy, low-temperature impurity breakdown in the diode base is accompanied by hysteresis of its conduction; in the diode of the second type, the impurity breakdown occurs in soft form. In the pre-breakdown region, the results obtained for the diodes of both types, agree completely with existing picture of non-ohmic hopping conduction in spite of significant space inhomogeneity of the diode structures and non-equilibrium character of the transport in them. In the post-breakdown region, the certain peculiarities are available. For the first time the activationless hopping conduction has been revealed in crystalline silicon.

Effect of magnetic field on hysteretic characteristics of silicon diodes under conditions of low-temperature impurity breakdown

Effect of magnetic field on hysteretic characteristics of silicon diodes under conditions of low-temperature impurity breakdown

Concerning the nature of relaxation oscillations in silicon diodes in the cryogenic temperature region

Time-resolved measurements have been performed of periodic oscillations in the voltage drop across a silicon diode which is fed by stabilized direct current (the situation for temperature measurement) in the region of instability connected with low-temperature impurity breakdown. Analysis of this effect was made on the base of simultaneous consideration of current–voltage characteristics of the diode under the same conditions. From these characteristics, by means of a new analytical method, the voltage-dependent series resistance, the breakdown voltage of the diode base, and equivalent diode capacity responsible for the observed oscillations have been determined. For the first time, practically linear relation between the feeding current and the oscillations frequency has been explained. This relation follows from the fact of approximate constancy of the charge accumulated by the equivalent diode capacity before the breakdown (irrespective of the feeding current value).

Simulation of longitudinal instabilities in filamentary current flow during low-temperature impurity breakdown in semiconductors

Nonlinear semiconductor transport simulations based on the WIAS-TeSCA code are presented. Various regimes of low-temperature breakdown and current filamentation in n-GaAs are investigated using a drift-diffusion model with nonlinear generation-recombination kinetics. Nonlinear charge density waves are found in two-dimensional simulations of a point contact geometry with and without an additional perpendicular magnetic field. The numerical simulations of the nonlinear spatio-temporal dynamics are complemented by a linear stability analysis which reveals the possibility of undamped longitudinal fluctuations in the filamentary regime.

Spatiotemporal PL imaging of current density filaments during impact ionization avalanche in high-purity n-GaAs

Image patterns of current density filaments formed during low-temperature impurity breakdown in high-purity n-GaAs have been investigated at 4.2 K by means of the spatiotemporal photoluminescence (PL) patterns. Under a pulsed voltage with the pulse width of w=18.0 μs and the repetition frequency of 8.0 kHz, a current density filament can be observed as a quenched PL pattern. Besides, anomalously bright PL pattern was observed along the filament boundaries. With a short pulse of w=785 ns, the bright PL pattern was formed inside the current filament. The anomalous enhancement of the PL intensity was attributed to the electron-impact formation and/or the hole-impact formation of the excitons bound to ionized donors during the impact ionization avalanche of the neutral shallow donors.

Electron mobility measurement inn−GaAsat low-temperature impurity breakdown

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Magnetoresistance effect of a current density filament in n-GaAs

Magnetoresistance of a current density filament formed by the low-temperature impurity breakdown has been measured in high-purity n-GaAs samples at 4.2 K, under magnetic fields of less than 260 mT. The resistivity of the bendable filament was measured as a function of the magnetic field intensity; it shows a good agreement with the calculated results based on ionized impurity scattering theory. For a relatively low applied electric bias, the magnetic field induces an instability of the filament, whose mechanism is discussed in detail.

Ghost pattern images of a current density filament formed by low-temperature impurity breakdown in n-GaAs

Ghost pattern image of a current density filament has been investigated in n-GaAs at 4.2 K. Applying a pulse voltage above the breakdown voltage, a current density filament is observed. After the pulse voltage is switched off, the ghost pattern of the filament persists due to the Joule heating effect.

Nonlinear spatio-temporal dynamics in semiconductors

We review recent theoretical advances in the modeling and computer simulation of complex non-linear spatio- temporal dynamics of charge carriers in semiconductors. Among the particularly instructive examples are investigations of current filaments in doped semiconductors in the regime of low temperature impurity breakdown. The nascence of current filaments in thin GaAs films with different contact geometries, including circular samples (Corbino disks) with symmetry breaking instabilities, is investigated, and the role of global couplings induced by the operating load circuit is analysed.

Discontinuities and Hysteresis in the I–V Characteristics of n-GaAs at Low Temperatures

We present experimental investigations of current filamentation in n-GaAs films in the regime of low-temperature impurity breakdown. Using a laser-scanning microscope, we were able to reconstruct current filaments in biasing regions of multistability. It is shown that discontinuities and hysteresis frequently observed in current-voltage characteristics are due to the interaction of filaments with material imperfections. In particular filaments remain in energetically unfavourable configurations when squeezed or pinned by defects.

Symmetry-breaking multiple current filamentation in n-GaAs

We report on theoretical investigations of the nasence of current filaments in thin film n-GaAs samples with two concentric circular contacts (Corbino disks). For a constant applied voltage in the regime of low-temperature impurity breakdown, a radially symmetric impact ionization front breaks up into streamers forming pre-filaments, among which a winner-takes-all dynamics sets in due to global coupling. On sweeping the external bias we find the spontaneous appearance of multiple stable filaments and hysteresis. In a perpendicular magnetic field the filaments are bent due to the Lorentz force.

Direct experimental observation of the Hall angle in the low-temperature breakdown regime ofn−GaAs

Using the technique of photoluminescence imaging during electrical transport in crossed electric and magnetic fields, the rotation of the current flow direction has been observed. The rotation angle is identically the Hall angle. As a model system, a thin n-type GaAs layer in the regime of low-temperature impurity breakdown has been used, generating filamentary current patterns. The measurement of the Hall angle allows one to determine the mobility inside current filaments.

Visualization of lateral movement of current-filaments in n-GaAs

In the regime of low-temperature impurity breakdown the influence of a magnetic field on current filaments yields complex voltage oscillations. With a new optical technique the spatio-temporal dynamics of filaments involving nucleation, lateral movements and extinction have been visualized corresponding to a certain type of electrical oscillation.

Low-temperature impurity breakdown in semiconductors: an approach towards efficient device simulation : R.E. Kunz, E. Scholl, R. Nurnberg and H. Gajewski. Solid-State Electronics, 1996, 39(8), 1155

Low-temperature impurity breakdown in semiconductors: an approach towards efficient device simulation : R.E. Kunz, E. Scholl, R. Nurnberg and H. Gajewski. Solid-State Electronics, 1996, 39(8), 1155

Influence of external circuits on filamentarycurrent flow during impurity breakdown in n -typeGaAs

Two-dimensional simulations are performed of low-temperature impurity breakdown in an n-type GaAs film connected to a capacitive and resistive external circuit under current controlled conditions. The results confirm that the transition between nearly-insulating and highly-conductive states, where a current filament is formed or decays in the sample, is synchronised with the charging and discharging of a parallel capacitor. Our simulations also indicate a mechanism for self-sustained relaxation oscillations.

Formation of current filaments in n-type GaAs under crossed electric and magnetic fields

We present two-dimensional simulations of current filaments in the regime of low-temperature impurity breakdown in thin n-GaAs films under the influence of a magnetic field perpendicular to the sample plane. Our simulations show that current filaments are bent by the Lorentz force and their width and curvature increase with magnetic-field strength. Significant asymmetry of the electric fields is observed at opposite filament boundaries. These results agree well with experiments. It is also revealed by simulations that impurity breakdown is accelerated by the presence of an external magnetic field. This is attributed to a finite Hall field inside the filaments.

Traveling carrier-density waves in n-type GaAs at low-temperature impurity breakdown.

We present a model for traveling charge-density wave instabilities in a semiconductor revealing S-shaped negative differential conductivity. It is based on microscopic generation-recombination rates including impurity impact ionization, which are obtained from Monte Carlo simulations. By a linear stability analysis and by numerical solution of the full nonlinear system we show that traveling-wave instabilities occur in the regime of both negative and positive differential conductivity. Our simulations give detailed insight into the spatiotemporal dynamics of the instabilities, and explain self-generated small-amplitude oscillations observed at the onset of breakdown. \textcopyright{} 1996 The American Physical Society.

Spatial structure of impact-ionization-induced current filaments in n-GaAs films

We present theoretical and experimental investigations of current filaments in thin n-GaAs films in the regime of low-temperature impurity breakdown. Simulations combining a Monte Carlo approach for the scattering and generation - recombination processes with a drift-diffusion model on a two-dimensional spatial domain yield detailed information about the distribution of the electron densities, electron temperature, current density and electric field. The theory is confirmed by spatially resolved measurements using a novel technique of quenched photoluminescence.

Dynamics of nascent current filaments in low-temperature impurity breakdown.

We present two-dimensional simulations showing the spatiotemporal dynamics of the formation of current filaments in n-type GaAs films in the regime of impurity impact ionization breakdown. From the spatial distribution of carrier densities, electron temperature, current density, and electric field for nascent and for fully developed filaments, we find a three-stage scenario for breakdown: (i) front creation and propagation from the cathode, (ii) stagnation in the phase of a rudimentary filament, (iii) filament growth. Our model combines semiclassical rate equations with microscopic transport parameters, which are obtained from Monte Carlo simulations. \textcopyright{} 1996 The American Physical Society.

Tuning of semiconductor oscillators by chaos control

It is demonstrated theoretically that a stable and tunable semiconductor oscillator can be designed by using a novel method of chaos control. By application of a small time-continuous delayed feedback voltage control signal, different unstable periodic orbits embedded in the chaotic attractor of a semiconductor can be stabilized. Thus different modes of self-generated periodic voltage oscillations can be selected, for example by choosing an appropriate delay time. This is illustrated for two different oscillation mechanisms involving hot-carrier transport: (i) self-generated oscillations under crossed electric and magnetic fields in the regime of low-temperature impurity breakdown (dynamic Hall effect), and (ii) driven real-space transfer oscillations in modulation-doped heterostructures.