4. Investigation of the mechanism of ultrafast high-current switching in semiconductors based on impact-ionization front.

Silicon closing switches with successive breakdown mode of diode structures based on a superfast ionization front have been studied. In a coaxial line with a wave impedance of 48 Ω, pulses with amplitude above 100 kV, peak power of 280 MW, and a rise time of 40 ps at an amplitude level of 0.3–0.9 were obtained. The maximum output voltage rise rate is 2 MV/ns at a switching current peak density of 60 kA/cm². Numerical simulation shows that the switching time of individual structures of the device is 7–15 ps at a reverse voltage rise rate of >100 kV/ns per structure under experimental conditions. The electric field in the p–n junction reaches the Zener breakdown threshold (~10⁶ V/cm), as a result of which the switching mechanism based on the tunneling-assisted impact-ionization front was realized.

The impact-ionization mechanism for switching power thyristor silicon structures to a conducting state by a short overvoltage pulse has been realized. Such a triggering mechanism allows increasing the rate of current rise by approximately two orders of magnitude compared to the traditional injection mechanism of a thyristor triggering by a current pulse through the gate electrode. When the voltage pulse is applied to the main electrodes of the thyristor with a voltage rise rate of units of kV/ns, the time for switching the thyristor to the conducting state is in the range of 200–400 ps, which corresponds to the average velocity of the front ionization wave 10–20 times higher than the saturated velocity of the carriers.

It has been established experimentally and by numerical simulation methods that the main factor determining the characteristics of the process of impact-ionization switching of power thyristors is the voltage rise rate of the triggering voltage dU/dt. An increase in the value of dU/dt leads to an increase in the electric field at which impact-ionization wave is excited. This decreases the time of the thyristor transition to the conductive state, increases the active area of the structure through which the current passes, and increases the temperature at which the impact-ionization wave can be triggered.

Thyristor switches with the impact-ionization switching mechanism have been developed and investigated. At current pulse duration of about 1 μs, the thyristor switch has an operating voltage of 20 kV, allows passing a peak current of 45 kA with an initial current rise rate of 130 kA/μs, and has a switching efficiency of 85–90%. At a pulse width of 25 μs, the switch operates at a charging voltage of 5 kV, discharges a capacitive storage with energy of 12 kJ and provides a peak current of 200 kA with a current rise rate of 58 kA/μs, and has a switching efficiency of 97%.

Main publications: 12, 14, 18–19, 24–25, 27–30.