Novel Closing Switches on the Base of Fast Ionization Fronts in Semiconductors

Abstract

Summary form only given. Subnanosecond switching of Si diode under fast (> 1 kV/ns) overvoltage in reverse direction was observed for the first time in 1979. Later it was shown that very efficient closing switches can be designed on the basis of this phenomenon in the p+npn+ dynistor structures. These devices - called fast ionization dynistors (FIDs) - have become the main elements of high power pulse generators of nano and subnanosecond range. Physical basis of fast switching of FIDs is the passage of fast ionization front in the wide n-base of the p+npn+ dinistor structure. The impact ionization in the neutral part of the n-base is considered as a source of free carriers that initiate this passage. Recently we found that tunnel emission from deep (~ 0.5 eV) electron traps is the possible source of free carriers for ionization front triggering. These traps are produced in the n-base during the manufacturing process. Neutral part of the n-base is not necessary in this case. Hence the total thickness of the base layer can be considerably reduced. As a result the residual voltage just after switching (0.1-0.5 ns) as well as during high current conducting mode (10-100 ns) decreases several times. Devices with such triggermg mechanism are called deep level dynistors (DLDs). Several types of DLD-based generators will be discussed in this presentation to illustrate these devices application areas: (i) nitrogen laser pumping (15 kV, 1 kA, 2 ns, 100 Hz), high voltage pulse generator (40 kV, 2kA, 3 ns), high power pulse generator (25 kV, 5 kA, 300 ns) for triggering the RSD-based switch (25 kV, 200 kA, 500 microsec) used for high power solid-state laser pumping. Computer simulations show that overvoltage with 10 kV/ns raise rate applied to the diode without any traps gives a possibility to achieve the electric field strength as high as 106 V/cm at the pn junction. Then free electrons are generated via band-to-band tunneling in the region of highest electric field and initiate passage of superfast ionization front with velocity ~5 108 cm/s. Typical turn-on time in this case can be as short as 20 ps.