It is experimentally established that high-voltage GaAs diodes maintain conducting state with low residual voltage after switching to the conducting state in the delayed impact-ionization mode. The duration of the constant current in the reversely-biased structure is determined by the duration of the applied rectangular voltage pulse (up to 100 ns) and significantly exceeds drift extraction and recombination times. The discovered effect of self-supporting conducting state resembles the lock-on effect in optically activated GaAs semiconductor switches and S-diodes with deep centers. The effect can be explained by shock ionization in narrow collapsing Gann domains.

Switching of a high-voltage GaAs diode to the conducting state in the delayed impact-ionization mode is simulated and the results are compared with experimental data. It is shown that the effect of long-term (up to 100 ns) sustaining of the conducting state of the diode after switching is due to the appearance of narrow (of the order of a micrometer) ionizing Gunn domains, the so-called collapsing domains, in the electron-hole plasma. Impact ionization in collapsing domains and in the edge (cathode and anode) domains of a strong electric field (~300 kV/cm) maintains a high concentration of nonequilibrium carriers (≥1017 cm-3) during the entire duration of the applied reverse polarity voltage pulse.