160 ISSN 1063-7850, Technical Physics Letters, 2018, Vol. 44, No. 2, pp. 160–163. © Pleiades Publishing, Ltd., 2018. Original Russian Text © V.I. Brylevskiy, I.A. Smirnova, N.I. Podolska, Yu.A. Zharova, P.B. Rodin, I.V. Grekhov, 2018, published in Pis’ma v Zhurnal Tekhnicheskoi Fiziki, 2018, Vol. 44, No. 4, pp. 66–73. Experimental Observation of Delayed Impact-Ionization Avalanche Breakdown in Semiconductor Structures without p–n Junctions V. I. Brylevskiy, I. A. Smirnova, N. I. Podolska, Yu. A. Zharova, P. B. Rodin*, and I. V. Grekhov Ioffe Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia *e-mail: rodin@mail.ioffe.ru Received October 18, 2017 Abstract—We have experimentally studied the dynamics of impact-ionization switching in semiconductor structures without p–n junctions when subnanosecond high-voltage pulses are applied. Silicon n + –n–n + type structures and volume ZnSe samples with planar ohmic contacts exhibit reversible avalanche switching to the conducting state within about 200 ps, which resembles the well-known phenomenon of delayed ava- lanche breakdown in reverse-biased p + –n–n + diode structures. Experimental data are compared to the results of numerical simulations. DOI: 10.1134/S1063785018020177 High-voltage pulses with steep fronts are used to initiate avalanche breakdown and create conducting electron–hole plasma in systems of two types: semi- conductor diode structures with planar contacts [1–3] and semiconductor crystals with “point” contacts [4]. Semiconductor diode structures switched by short high-voltage pulses are also called “pulse sharpeners.” The switching of a pulse-sharpening diode takes less than 100ps and starts at a voltage significantly exceed- ing that of steady-state breakdown [1, 5]. This phe- nomenon, known as the “delayed impact-ionization avalanche breakdown of semiconductor diode struc- tures” [1], was originally discovered in silicon-based and arsenide–gallium structures [6, 7] and used in pulsed power electronics [2, 3, 8–10]. The transverse size of a pulse-sharpening diode significantly exceeds the distance between planar contacts, so that the elec- tric field that provides ionization avalanche in the n-base is quasi-uniform over the area of the structure and the avalanche generation of carriers can occur (at least in principle) over the entire volume of the struc- ture. In contrast, a high-voltage pulse with a steep front in semiconductors with point contacts initiates the formation and propagation of streamers [4], that is, the generation of dense electron–hole plasma within narrow filamentary regions. Previous investiga- tions [4] were aimed at creating impact-ionization lasers. The present work was devoted to the first experi- mental investigation of impact-ionization avalanche breakdown in semiconductor structures without p–n junctions. The experiments were performed with sili- con structures of n + –n–n + type and volume zinc sele- nide (ZnSe) samples with planar ohmic contacts. It was established that a high-voltage pulse with a steep front in these systems initiates ultrafast (within about 200 ps) switching to the conducting state. A compari- son of experimental data to the results of numerical simulations leads to the conclusion that nonequilib- rium electron–hole plasma is generated in the most part structure volume. Silicon n + –n–n + diode structures were manufac- tured from n-type silicon with dopant concentration N = 1.7 × 10 14 cm –3 by the same diffusion technology as that used previously in obtaining p + –n–n + struc- tures for pulse-sharpening diodes [5] with similar dimensions: diameter of about 1 mm and total thick- ness of about 200 μm. The thickness of n + layers formed using phosphorus diffusion was ~10 μm. In addition, a series of n + –n–n + diode structures were manufactured with ~60-μm-thick n + layers and 80-μm-thick n layers. Zinc selenide samples were manufactured from ZnSe(111) plates with a thickness of 450 μm and 0.5–1-μm-thick indium ohmic contact layers [11] formed by two-stage deposition with inter- mediate annealing. The samples were cut out in the form of disks with a diameter of 1 mm. The experimental setup comprised the generator of bell shaped pulses with nano- and subnanosecond rise time, the resistive coupler, two measuring circuits with high-voltage attenuators, and a 20-GHz strobo- scopic oscilloscope. The resistive coupler also played the role of a sample holder, where the structure was