Planar Gas Discharge Research Articles

Transition from periodic to chaotic oscillations in a planar gas discharge-semiconductor system

The work studies the transition from periodic to chaotic oscillations in a dc-driven planar gas discharge with a high-ohmic electrode. The applied voltage and resistance of the semiconductor layer act as control parameters. The oscillations occur in the subnormal discharge regime. The bifurcation diagram and Lorenz map characterizing transition of this system to chaos through period-doubling bifurcations are obtained. Numerical models employed are based on the drift-diffusion theory of gas discharges. The effect of two modelling approaches, namely the ‘simple’ fluid model and the more detailed ‘extended’ fluid model, is considered. The calculations showed that the results obtained by these two approaches are different in quantitative terms, however, qualitatively similar in terms of the dynamic behavior of the system as a function of the control parameters.

Numerical evidence of spontaneous division of dissipative solitons in a planar gas discharge–semiconductor system

This work deals with the formation of patterns of spatially localized solitary objects in a planar semiconductor gas-discharge system with a high Ohmic electrode. These objects, known as dissipative solitons, are generated in this system in the form of self-organized current filaments, which develop from the homogeneous stationary state by the Turing bifurcation. The numerical model reveals, for the first time, evidence of spontaneous division of the current filaments in this system, similar to that observed in the experiment, in the physically relevant parameter regime.

Transition from homogeneous stationary to oscillating state in planar gas discharge–semiconductor system in nitrogen: Effect of fluid modelling approach

A laterally extended dc-driven system of planar gas discharge with a high-ohmic semiconductor electrode is considered. Numerical models are based on the fluid equations of plasma with drift-diffusion approximation for particle fluxes. The effect of different modelling approaches (with simpler and more detailed treatment of the electron transport and plasma chemical reactions) is analyzed. Bifurcation diagrams separating stable stationary states of the system from oscillatory states are derived and compared with the experimental data.

3D simulation of hexagonal current pattern formation in a dc-driven gas discharge gap with a semiconductor cathode

The formation of hexagonal current pattern in a dc-driven thin planar gas discharge gap with a semiconductor cathode is studied on the basis of a 3D drift-diffusion discharge model. The model includes continuity equations for electron and ion densities, the electrostatic equation for electric field and heat conduction equation for gas temperature. Solving these equations by the time-relaxation method, we investigate the genesis of ordered current pattern and its subsequent rearrangement into the hexagonal pattern, starting from initial homogeneous discharge state without any initial perturbations. For the case of the dc discharge with a semiconductor cathode and cryogenic conditions, the 3D calculation has been performed for the first time. The resulting current pattern is in agreement with experiment. The results of the simulation confirm that the discharge instability and the patterns formation are due to an ionization-overheating (thermal) mechanism, as was proposed before in [Raizer Yu P and Mokrov M S 2010 J. Phys. D: Appl. Phys. 43 225204] on the basis of approximate theory.

Exploration of the Townsend regime by discharge light emission in a gas discharge device

The Townsend discharge mechanism has been explored in a planar microelectronic gas discharge device (MGDD) with different applied voltages U and interelectrode distance d under various pressures in air. The anode and the cathode of the MGDD are formed by a transparent SnO2 covered glass and a GaAs semiconductor, respectively. In the experiments, the discharge is found to be unstable just below the breakdown voltage Ub, whereas the discharge passes through a homogeneous stable Townsend mode beyond the breakdown voltage. The measurements are made by an electrical circuit and a CCD camera by recording the currents and light emission (LE) intensities. The intensity profiles, which are converted from the 3D light emission images along the semiconductor diameter, have been analysed for different system parameters. Different instantaneous conductivity σt regimes are found below and beyond the Townsend region. These regimes govern the current and spatio-temporal LE stabilities in the plasma system. It has been proven that the stable LE region increases up to 550 Torr as a function of pressure for small d. If the active area of the semiconductor becomes larger and the interlectrode distance d becomes smaller, the stable LE region stays nearly constant with pressure.

Self-Organized Patterns in Planar Low-Temperature AC Gas Discharge

Various partly strange self-organized patterns can be observed experimentally in the distribution of the luminescence radiation density and the corresponding current density in planar low-temperature dielectric barrier gas discharge systems.

Simulation of current filamentation in a dc-driven planar gas discharge–semiconductor system

We have performed a theoretical study of self-organized current filamentation in a dc-driven planar gas discharge–semiconductor system at very low currents and under cryogenic conditions. The discharge instability and the observed formation of current filaments are explained by a thermal mechanism, as proposed in our previous paper. We have found, for the first time, a stationary periodic current structure in a two-dimensional Cartesian geometry from first principles, by numerically solving the general system of continuity equations for ions and electrons, the Poisson equation for the electric field in the gas, together with the equation for gas temperature and the equation for electric field in the semiconductor. The space charge induced electric field redistribution, which usually leads to a discharge instability and is automatically included in the first three equations of the system, is practically absent at the very low currents considered, and thus it cannot be responsible for the discharge instability. This is why another mechanism of filamentation (thermal) should be considered. The calculated periodic current structure agrees with the hexagonal current pattern observed in the experiment, as well as with the periodic current structure found in the frame of the previously developed simple model. This serves as a corroboration of the fact that the thermal effect is essential for pattern formation under the conditions considered.

A simple physical model of hexagonal patterns in a Townsend discharge with a semiconductor cathode

This paper explains the observed effect of self-organization in a dc driven planar gas discharge–semiconductor system resulting in a hexagonal current pattern under cryogenic conditions. It is shown that the electric field redistribution usually causing a falling current–voltage characteristic (CVC) of the Townsend discharge and the discharge instability cannot provide the formation of the hexagonal pattern. Another mechanism is proposed which gives a necessary, high negative slope of the CVC under cryogenic conditions. This is a well-known thermal mechanism. Due to Joule heat release gas is heated and expands; hence, a lower field and voltage are required to sustain the discharge at a given current. Simple approximate equations describing non-stationary spatially inhomogeneous states in the gas discharge–semiconductor system are derived from physical considerations. The numerical integration of the obtained equations with a realistic parameter set gives the hexagonal current pattern. By simplifying these equations, we found analytically the current and the discharge voltage distributions of the hexagonal type and a simple formula for the distance between adjacent current filaments. The analytical solution allows one to investigate the roles of different factors and extract from experiment the negative differential resistance of the discharge, which is the main parameter in the problem of the discharge instability and the current structure formation.

Gas-discharge system with a zeolite electrode

A zeolite plate with push contacts is placed in a chamber filled with air at a controllable pressure, and the current-voltage characteristics of the zeolite plate are measured as a function of the air pressure in the chamber. It is found that the gas in zeolite pores ionizes and, accordingly, the number of electrons in the pores grows. It is shown that such a plate used as a cathode in a planar gas-discharge cell considerably reduces the ignition voltage of the gas discharge.

Effect of surface conduction in the semiconductor electrode on the distribution of the gas-discharge current

A planar gas-discharge structure, in which one of the electrodes is a high-resistivity semiconductor capable of providing stable uniform distribution of the current and the gas-discharge’s light emission within the entire volume of the gas-discharge gap, is studied. It is established that the effect of the semiconductor electrode on the distribution of the steady-state current in the gas-discharge gap is associated with the conductivity of the electrode’s surface layer, whereas the resistance of the semiconductor bulk defines only the load resistance. It is experimentally shown that local metallization of the semiconductor surface results in current pinching in the metallized areas. It is concluded that the basic physical effect that limits the probability of current pinching and provides stable discharge is associated with the electric field orthogonal to the current pinch at the point of its contact with the semiconductor. A qualitative analysis of this effect is presented. The obvious condition of smallness of this field compared to the longitudinal field in the pinch allows two types of pinching: one corresponds to the formation of a solitary pinch at a fairly high conductivity of the semiconductor’s surface layer, whereas the other corresponds to the formation of a large number of pinches, almost totally covering the surface of the electrode, at a low surface conductivity.

Semiconductor gas discharge IR image converter with internal image amplification

The possibility of locally increasing the gas discharge light emission (GDLE) in the UV and visible range generated by a planar semiconductor gas discharge IR image converter system (SGDICS) in the wide pressure range (266–93 325 Pa) has been studied. The use of gas discharge gap with microcapillary multichannels spacer (MCS) and an IR light to excite the GaAs photocathode of the SGDICS leads to increase in the GDLE intensity. Electrons entering the multichannels of the discharge gap are multiplied in the electrical field by the avalanche mechanism, so that current increases in the discharge gap with microcapillary MCS. In this system, the local intensity of GDLE exceeds the intensity of uniform GDLE in the SGDICS by the same factor as the working area of the photocathode exceeds the total active area of the MCS. It is experimentally demonstrated that gas discharge gap with microcapillary MCS of an SGDICS can operate as an effective internal image intensifier with gain values of 20.

Memory effect in semiconductor gas discharge electronic devices

The memory effect in the planar semiconductor gas discharge system at different pressures (15–760 Torr) and interelectrode distances (60–445 µm) was experimentally studied. The study was performed on the basis of current–voltage characteristic (CVC) measurements with a time lag of several hours of afterglow periods. The influence of the active space charge remaining from the previous discharge on the breakdown voltage (UB) has been analysed using the CVC method for different conductivities of semiconductor GaAs photocathode. CVC showed that even a measurement taken 96 h after the first breakdown was influenced by accumulated active particles deposited from the previous discharge. Such phenomena based on metastable atoms surviving from the previous discharge and recombined on the cathode to create initial electrons in the avalanche mechanism are shown to be fully consistent with CVC data for both pre-breakdown and post-breakdown regions. However, in the post-breakdown region pronounced negative differential conductivity was observed. Such nonlinear electrical property of GaAs is attributed to the existence of deep electronic defect called EL2 in the semiconductor cathode material. On the other hand, the CVC data for subsequent dates present a correlation of memory effect and hysteresis behaviour. The explanation for such a relation is based on the influence of long lived active charges on the electronic transport mechanism of semiconductor material.

Stability and current behaviour in semiconductor gas discharge electronic devices

Breakdown and range of stable discharge glow in a homogeneous dc electric field are studied at various distances d between the electrodes and different inner diameters D (5, 9, 12, 18 and 22 mm) of GaAs semiconductor cathode areas. The current–voltage characteristics of the gas discharge system have been studied in a wide range of pressure p (16–760 Torr), interelectrode distances d (10 µm–5 mm) and conductivities of the GaAs cathode. The initiation of electrical breakdown as a result of secondary electron emission from the semiconductor cathode in low gas pressure is presented in this paper. In a planar gas discharge cell with diameters much larger than an interelectrode distance, the effects of different parameters (overvoltage, electrode separation, diameter and conductivities of the GaAs cathode, gas pressure, glow current, etc) on electrical breakdown and spatial stabilization of the current have been studied. The distributed resistance of photosensitive semiconductor cathode and the impact of the ionizing component of the discharge plasma on the control of the stable operation of a planar gas discharge system at atmospheric pressure are also investigated. Through spatially uniform irradiation of the semiconductor cathode, non-stationary states which are non-homogeneous can be generated in a system. The loss of stability is primarily due to the formation of a space charge of positive ions in the discharge gap which changes the discharge from the Townsend to the glow type.

Study of light emission amplification in a semiconductor gas discharge system

Light emission in the UV and visible range generated by a planar semiconductor gas discharge system and the possibility of locally increasing the gas discharge light emission (GDLE) in a wide pressure range (2–700 Torr) has been studied. The use of gas discharge gap with microcapillary multichannels spacer (MCS) and an IR light to excite the GaAs photocathode of the system leads to an increase in the GDLE intensity. Electrons entering the multichannels of the discharge gap are multiplied in the electric field by the avalanche mechanism, so that current increases in the discharge gap with microcapillary MCS. In this system the local intensity of GDLE exceeds the intensity of uniform GDLE in the gas discharge system by the same factor as the working area of the photocathode exceeds the total active area of the MCS. Due to the very small electrode gap width we can describe the behaviour of the charged particles in the electric field of our system with the dc Townsend breakdown theory, depending on the pressure range.

Spontaneous division of dissipative solitons in a planar gas-discharge system with high ohmic electrode

In this Letter we report on the division of electrical current filaments in a planar semiconductor gas-discharge system with high ohmic electrode that we refer to as dissipative solitons. The effect is observed for stationary and propagating, as well as for isolated and for dense arrangements of filaments. For large spatial density of dissipative solitons, processes of their generation and annihilation seem to give rise to a specific kind of spatio-temporal chaotic dynamics.

Analysis of prebreakdown current in a gas discharge system with a semiconducting cathode

Results are presented of an analysis of the prebreakdown current of a Townsend discharge in a planar gas discharge system with a GaAs semiconductor cathode for a gap thickness of 45 µm and gas pressures of 6.9, 8.9, 34.2 and 36.9 kPa. IR radiation excites the cathode in the system, thus controlling the current density in the gas discharge layer. It is shown that the prebreakdown current is caused by electron emission from the semiconductor surface. The present experimental investigations show that the prebreakdown current decreases anomalously with increase of the feeding voltage and that it also decreases under the illumination of a semiconductor cathode. Both these anomalies depend on gas pressure. The current density change through the cross-section of the discharge gap, i.e. the appearance of the spatio-temporal self-organization of non-linear dissipative systems, causes these observed effects. These characteristics of the system can be applied for fast IR imaging and a high speed UV light source.

Current instability in a planar gas discharge system with a large-diameter semiconductor cathode

The current instability in a planar gas discharge system is studied experimentally in a wide range of the gas pressure, p (44–550 Torr), interelectrode distance, d (45–330 µm), and diameter, D (5, 9, 12, 18, 22 mm), of the electrode areas of the semiconductor cathodes. While being driven with a stationary voltage, it generates current instabilities with different amplitudes of the oscillation. Through spatially uniform irradiation of the semiconductor cathode, non-stationary states which are non-homogeneous can be generated in a system. It is shown that under the experimental conditions the discharge gap played only a passive role and was not responsible for the appearance of the current instability. At the same time, for different diameters, D, of the electrode an expanded range of current oscillations is observed. The pronounced N-type negative differential resistance is observed in the current–voltage characteristic of a planar gas discharge system with a large-diameter semiconductor cathode.

A Large Emitting Area UV Light Source With Semiconductor Cathode

Light emission in the ultraviolet (UV) and visible (blue) range (330-440 nm) generated by a planar gas discharge system and the possibility of locally increasing the discharge light emission for a given photosensitivity of a planar GaAs semiconductor cathode has been studied. The use of metallic patched concentrators with an area of S=5/spl times/10/sup -4/ cm/sup 2/ and a density of 400 cm/sup -2/ leads to a fivefold increase in the gas light density. In a system with metallic patched concentrators, the local density of gas discharge light exceeds the density of uniform gas discharge light in the ionization system as many times as the working area of the semiconductor cathode exceeds the total area of the current concentrators. By using the infrared light to excite the semiconductor cathode of the system, we have shown that the uniform discharge light emission of the device with N/sub 2/ in the gap can serve as a source of UV radiation with a large emitting area of GaAs cathode if gas pressure and electric field are sufficiently high. Moreover, the use of metallic patched concentrators prolongs the working time of the cathode. The filamentation was primarily due to the formation of a space charge of positive ions in the discharge gap, which changed the discharge from the Townsend to the glow type.

Behaviour of current in a planar gas discharge system with a large-diameter semiconductor cathode

Gas breakdown in air in a planar gas discharge system was studied experimentally at various distances L between the electrodes and different diameters R of the electrode areas of the semiconductor cathodes. The cathode was irradiated on the back-side with light in a particular wavelength range that was used to control the photoconductivity of the material. The current–voltage characteristics of the gas discharge system with a large-diameter GaAs semiconductor cathode were studied in a wide range of the gas pressure p (28–550 Torr), interelectrode distances L (45–330 μm), and conductivities of the cathode. We show that for all experimental conditions the current density increases over the entire range of voltages U>Udc as the diameters R of the electrode areas increase. It is shown that, for arbitrary geometric dimensions of the semiconductor cathode (in the range of L/R under investigation), the ratio of the breakdown electric field to the gas pressure holds constant (Edc/p)min≈const. at the breakdown curve minimum. The breakdown voltage Udc is a function of both the product of the gas pressure p by the distance L and the ratio L/R (Udc = f(pL,L/R).

Plasma spots in a gas discharge system: birth, scattering and formation of molecules

Experiments on a planar gas discharge device, where formation of spatial structures is of the Turing origin, demonstrate that particle-like states of a pattern can scatter at each other, form bound (“molecular”) states that propagate over the active area of the device, and generate additional quasi-particles in the course of collisions.