Shockley diode

A Shockley diode (four-layer diode) is a semiconductor device with a "pnpn" structure, equivalent to a thyristor with a disconnected gate. It is named after its inventor, William Shockley, co-inventor of the transistor and Nobel laureate.

The Shockley diode is in a high-impedance state at low voltages. When a switching voltage is reached, which is in the range of 10 V to 250 V depending on the device, it triggers like a thyristor and switches into a conductive state where the residual device voltage falls to some 1-2 V. The resultant negative resistance characteristic can be used for trigger circuits, flipflops or relaxation oscillators.

Shockley diodes were among the first commercially available silicon semiconductor devices in the late 1950s.