Picosecond-range switching of high-voltage Si diode due to the delayed impact-ionization breakdown: Experiments vs simulations

The effect of delayed impact ionization breakdown initiated in a high-voltage Si or GaAs p+nn+ diode by a steep voltage ramp leads to 100 ps avalanche transient from the blocking to conducting state. Here, measurements of the voltage and current dependences in the Si diode exhibiting 100-ps kilovolt switching are presented together with simulations with focus on comparison. Device voltage and current are measured simultaneously and independently in a high-quality matched coaxial circuit. In simulations, we account for wave propagation and reflection processes in the coaxial driving/measuring circuit and for the inhomogeneity of the avalanche switching over the device cross section. This makes quantitative comparison with measurements possible. An agreement in switching time and transient characteristics can be achieved only under the assumption that a smaller part of the cross section is avalanching. The 100-ps switching time is formed not during the passage of superfast ionizing front in the “active” part of the device, as it is widely believed, but by the discharge time of the “passive part” over the conducting “active” part. The inner circuital current that flows within the device along the closed loop plays a dominant role in this process. Sources of initial carriers, the temperature dependence of the effect, and the limits of drift-diffusion transport model in describing the phenomenon of delayed breakdown are discussed.