Formation of the space charge region in diffusion p-n junctions under high-density current interruption |
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Authors: | I V Grekhov A S Kyuregyan |
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Institution: | 1. Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021, Russia 2. Lenin All-Russia Institute of Electrical Engineering, Moscow, 111250, Russia
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Abstract: | The recovery of diodes with diffusion p-n junctions in the case of high reverse current density j is analyzed. A condition for quasi-neutrality breaking in the diffusion layers with allowance for the dependence of charge carrier mobility μ on electric field strength E is obtained that is valid for a wide range of j. The problem of formation of the space charge region in a circuit with inductance L and resistance R is reduced to a system of two ordinary differential equations. Approximation of a numerical solution to this system makes it possible to derive crude analytical relationships between interrupted current density {ie88-1}, circuit parameters, diode parameters, and parameters of a forming voltage pulse (with amplitude V m and pulse rise time t p). The limiting parameters of a pulser with an inductive energy storage and current interrupter based on diffusion diodes are studied. The critical density of interrupted current {ie88-2} is determined at which the field in the space charge region near the anode reaches breakdown value E b and intense impact ionization by holes begins. The impact ionization decreases the rates of current decay and voltage increase in the space charge region. As a result, at {ie88-3}, t p starts increasing and the overvoltage factor of the pulser decreases. The value of V m corresponding to {ie88-4} is roughly given by {ie88-5}, where m is the number of diodes in the interrupter, ? is the permittivity of the semiconductor, {ie88-6} is the saturated drift velocity of holes, and l p is the depth of the p-n junction (diffusion depth). Theoretical predictions are confirmed by exact numerical simulation of the recovery process and qualitatively agree with the available experimental data. |
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