Dynamics of electron-hole plasma in semiconductor opening switches for ultradense currents

A physicomathematical model for calculating the dynamics of the electron-hole plasma in semiconductor opening switches for ultradense currents is developed. The model takes account of the real doping profile of a semiconductor p ⁺-p-n-n ⁺ structure and the following elementary processes in the electron-hole plasma: current-carrier diffusion and drift in high electric fields, recombination on deep impurities and Auger recombination, and collisional ionization in a dense plasma. The electrical pumping circuit of the opening switch is calculated by solving the Kirchhoff equations. The motion of the plasma in the semiconductor structure is analyzed on the basis of the model. It is shown that for ultrahigh pumping levels the interruption of the current in the opening switch occurs in the heavily doped regions of the p ⁺-p-n-n ⁺ structure and is due to saturation of the particle drift velocity in high electric fields. Zh. Tekh. Fiz. 67, 64–70 (October 1997)     

Effect of structure doping profile on the current switching-off process in power semiconductor opening switches

Using a physicomathematical model, the process of current breaking in power semiconductor opening switches was investigated in p ⁺-p-n-n ⁺ structures with different doping profiles. The model takes account of the actual doping profile of a structure, diffusion and drift of current carriers in a strong electric field, recombination via deep impurities and Auger recombination, and impact ionization in a dense plasma. The calculation of the electrical circuit of an opening switch is based on solution of Kirchhoff’s equations. It has been shown that in the nanosecond regime of breaking superhigh current densities with densities of the interrupted currents from a few to tens of kA/cm², the dominant factor in the current breaking process is the width of the p-region in the initial doping profile of a structure. An increase in the p-region width from 100 to 200 μm makes the velocity of the excess plasma front propagating in the p-region in the reverse pumping stage higher by a factor of 5–7. Higher propagation velocity of the plasma front makes the current breaking process more intensive, which is manifested in the shorter current breaking time and higher overvoltage across the opening switch.     

Luminescent Analysis of Blood Serum for Diagnostics of Pathological and Pre-Pathological States of Cancer Patients

Journal of Fluorescence - This study is devoted to the development of a methodological approach to mathematical analysis and data interpretation of blood serum phosphorescence intensity in cancer...     

On the electric activity of superfluid systems

The Keldysh theory of the superfluidity of a diluted electron-hole gas has been generalized to the case of the possible polarization of the pairs. It has been shown that the inhomogeneity of the system induces the dipole moment, which appears near the system boundaries and is proportional to the gradient of the particle density. It has been found that the quantized vortices in the magnetic field carry a real electric charge. The charge density in He II rotating at a rate of 10²s⁻¹ in a magnetic field of 10 T is about 10⁴ e cm⁻³, where e is the elementary charge.     

Logic-structure approach to the evaluation and prediction of physicochemical characteristics of organic compounds

An efficient method is proposed for computerized screening, highly effective for a number of properties of structures. This method is identical to the problem of classification, and it is solved by a pattern recognition method based on a logic-structure approach (method of logic correlations). Whether or not a substance belongs within a certain indicated range of properties is determined by the presence or absence of informative local features of topology of the compound's structure and the spatial positioning of the atoms.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1349–1355, June, 1990.We wish to express our appreciation to M. Kh. Klin for interest in this work and for constructive criticism.     

Effect of space charge on subnanosecond current cutoff in powerful semiconductor diodes

High-density current cutoff in an SOS diode is studied with a physicomathematical model including the space-charge effect. If the depth of the p-n junction exceeds 180 µm, the forward pumping time is less than 60 ns, and the backward pumping time is shorter than 20 ns, the subnanosecond cutoff of current with a density of several kiloamperes per square centimeter takes place. The cutoff mechanism is associated with the origination of three high-field zones at the stage of current cutoff: two zones on the p-side, which expand with a velocity close to the saturation value, and one on the n-side, which expands slowly. Taking the space charge into account reduces the role of avalanche multiplication and, as a consequence, improves the switching properties of the diode. It is found that a set of conditions for the electric circuit parameters that specify the pumping current duration and density and for the dopant profile in the semiconductor must be met for subnanosecond current cutoff to occur. The results are compared with experimental data and a model using a quasi-neutral approximation.