Yu. A. Astrov

HEXAGON AND STRIPE TURING STRUCTURES IN A GAS DISCHARGE SYSTEM

Abstract We report the observation of different scenarios of pattern formation in a dc driven two-dimensional semiconductor-discharge system. Transitions from the homogeneous state to stationary hexagon and stripe patterns are referred to as instabilities of Turing type. The underlying physical mechanism is discussed.

Speed properties of a semiconductor-discharge gap IR image converter studied with a streak camera system

Under certain experimental conditions a semiconductor‐discharge gap structure can be used as detector for spatiotemporal resolved measurements on IR radiation. With a streak camera system and a semiconductor laser diode (λ=1.3 μm), we investigate experimentally the speed properties of this kind of converter. The experimental results are compared with the predictions of a simple theoretical model.

HIGH SPEED CONVERSION OF INFRARED IMAGES WITH A PLANAR GAS DISCHARGE SYSTEM

The speed of conversion of infrared (IR) images by a planar semiconductor gas discharge system into the visible range has been investigated. Argon or nitrogen are used in the discharge gap having an electrode distance of 100 μm. Using pulse radiation from an IR laser to excite the system, we have shown that the characteristic response time of the device with the cryogenic discharge in the gap can lie in the submicrosecond range. This characteristic of the system can be applied for a fast IR imaging at a rate higher than 106 frame/s.

Experimental and numerical observation of quasiparticle like structures in a distributed dissipative system

Abstract We report on the experimental discovery of interacting quasiparticle like structures called filaments in a distributive system consisting of a high resistivity semiconductor layer in series with a narrow gas-discharge gap. The basic features of interacting filaments can be found in the numerical simulations of a simple reaction-diffusion system.

Glow dynamics in a semiconductor-gas discharge image converter

Transient phenomena which accompany the breakdown of gas in a semiconductor-gas discharge (SGD) system with 100 μm interelectrode distance have been studied experimentally and with numerical calculations. This system serves as the basis for an image converter operating in the infrared (IR) spectral region. The experiments are done for a cryogenic discharge in helium at a temperature close to that of liquid nitrogen. Depending on specific experimental conditions, oscillatory or aperiodic modes approaching to the steady-state current are observed after breakdown has been induced by a step-like voltage pulse. Numerical calculations of transient phenomena were performed for experimental conditions within the framework of the Townsend model, taking into account direct ionization, Penning ionization and secondary emission of electrons from the cathode. The main features of discharge kinetics obtained are in accordance with experimental data. At the same time, with the steady-state discharge current density vary...

Silicon with an increased content of monoatomic sulfur centers: Sample fabrication and optical spectroscopy

The effect of the high-temperature heating (at 1340°C) of sulfur-doped silicon samples and their subsequent quenching is studied. The results of such a treatment are analyzed on the basis of Hall-effect data obtained in the temperature range T = 78–500 K. It is shown that the heating duration strongly affects the relative concentrations of different types of deep sulfur-related centers. At comparatively short heating durations of t = 2–10 min, the concentration of quasi-molecular S2 centers and SX complexes substantially decreases, whereas the density of monoatomic S1 centers grows. At the same time, the heating of a sample is accompanied by a monotonic decrease in the total concentration of electrically active sulfur over time. The results obtained make it possible to give recommendations concerning the optimal conditions for the fabrication of samples with a high concentration of S1 centers. The absorption spectra of the samples show that the method is promising for the observation of a number of quantum-optical effects involving deep S1 donors in silicon.

Rotating waves in a planar dc-driven gas-discharge system with semi-insulating GaAs cathode

A primary destabilization of homogeneous discharge in form of rotating waves is observed in a planar dc-driven gas-discharge system with a semi-insulating GaAs cathode that exhibits nonlinear transport properties. The rotating waves are stable in the case of constant control parameters and are characterized by a monotonic decrease of rotation frequency with increasing supply voltage. It is shown that the nonlinearity of the semiconductor is essential for the generation of the pattern, whereas the gas serves to visualize it.

Spatiotemporal structures in a transversely extended semiconductor system

A semiconductor system with an N-shaped current-voltage characteristic can generate nonstationary structures that are inhomogeneous in the direction transverse to the current flow. In samples of semiinsulating GaAs with a large cross section, this effect is explained by a loss of stability of the regime of uniform domain motion.

Diffusion of interstitial magnesium in dislocation-free silicon

The diffusion of magnesium impurity in the temperature range T = 600–800°C in dislocation-free single-crystal silicon wafers of p-type conductivity is studied. The surface layer of the wafer doped with magnesium by the ion implantation technique serves as the diffusion source. Implantation is carried out at an ion energy of 150 keV at doses of 5 × 1014 and 2 × 1015 cm–2. The diffusion coefficient of interstitial magnesium donor centers (Di) is determined by measuring the depth of the p–n junction, which is formed in the sample due to annealing during the time t at a given T. As a result of the study, the dependence Di(T) is found for the first time. The data show that the diffusion process occurs mainly by the interstitial mechanism.

Development of photodetectors for image converters: Doping of silicon with selenium from the gas phase

High-speed recording of processes in the IR spectral range can be carried out using image converters of the “semiconductor photodetector + gas discharge gap” type. To develop photodetectors with the properties required for this purpose, the effect of the selenium vapor pressure PSe on the doping efficiency of single-crystal silicon with selenium has been studied. Selenium was introduced by diffusion in sealed quartz cells at a temperature of 1240°C in the pressure range PSe = 0.27–1.0 atm. Doped samples were studied by performing temperature measurements of the Hall effect. A heavy dependence of the concentration of the impurity centers introduced on PSe was observed. It was found that the doping effect is the same for starting crystals produced by floating zone melting and by the Czochralski method. The data obtained were used to fabricate photodetectors that can be employed in high-speed thermography with the use of the image converters under consideration.