The Mechanism of Superfast Switching of Avalanche ${S}$ -Diodes Based on GaAs Doped With Cr and Fe

The results of theoretical and experimental investigation of charge carrier transport in avalanche S-diodes based on
$\pi $
-
$\nu $
-n and
$\pi $
-n structures are presented. High-ohmic layers of the diodes were made by diffusion of deep chromium and iron acceptors into n-GaAs. It is shown that recharge of the deep acceptors in the avalanche regime should lead to expansion of the space charge region into the
$\pi $
-layer and formation of step-type current–voltage characteristics rather than the S-type. It has been found experimentally that the switching of the S-diode is superfast (the time of switching is less than the transient time of the carriers through the active region). The obtained results are in contradiction with the earlier proposed mechanism of deep-level recharging. Thus, this mechanism has been revised. The comparison of the obtained results with the literature data allows one to find the only mechanism of superfast switching, which is associated with generation of collapsing field domains due to the Gunn effect under the avalanche breakdown condition. According to the experiment, the switching time of S-diodes depends on the applied voltage and the type of the deep-level impurity. The S-diodes can operate in relaxation oscillator and sharper circuits. The use of the S-diodes in a sharper circuit with a moderate voltage rate of 10
¹¹
V/s allows generating the voltage pulses with amplitude of 700 V and a rising edge of 250 ps at a load of
$50~\Omega $
.