Subnanosecond avalanche switching in high-voltage silicon diodes with abrupt and graded $p$–$n$ junctions

The phenomenon of delayed avalanche breakdown in high-voltage silicon diodes has been studied for the first time using an experimental setup with specially designed resistive coupler as a part of a high-quality matched measuring tract. Three types of diode structures with identical geometric parameters and close stationary breakdown voltages within 1.1–1.3 kV have been studied, including $p^+$–$n$–$n^+$ structures with abrupt $p$–$n$ junctions and two different $p^+$–$p$–$n$–$n^+$ structures with graded $p$–$n$ junctions. Upon switching of all structures, a voltage step with an amplitude above 1 kV and a rise time of $\sim$ 100 ps at a breakdown voltage of about 2 kV is formed in the load. However, switching to a state with low ($\sim$ 150 V) residual voltage has been observed only in the structures with an abrupt p-n junction, while the voltage in structures with graded junctions only decreased to a level of $\sim$1 kV, which is close to the stationary breakdown voltage.