The Shockley diode (named after physicist

William Shockley William Bradford Shockley Jr. (February 13, 1910 – August 12, 1989) was an American physicist and inventor. He was the manager of a research group at Bell Labs that included John Bardeen and Walter Brattain. The three scientists were jointl ...

) is a four-layer

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...

diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diod ...

, which were one of the first semiconductor devices invented. It is a PNPN diode, with alternating layers of P-type and N-type material. It is equivalent to a

thyristor A thyristor () is a solid-state semiconductor device with four layers of alternating P- and N-type materials used for high-power applications. It acts exclusively as a bistable switch (or a latch), conducting when the gate receives a current ...

with a disconnected gate. Shockley diodes were manufactured and marketed by

Shockley Semiconductor Laboratory Shockley Semiconductor Laboratory was a pioneering semiconductor developer founded by William Shockley, and funded by Beckman Instruments, Inc., in 1955. It was the first high technology company in what came to be known as Silicon Valley to w ...

in the late 1950s. The Shockley diode has a negative resistance characteristic. It was largely superseded by the diac.

Working

Unlike other semiconductor diodes, the Shockley diode has more than one PN junction. The construction includes four sections of semiconductors placed alternately between the anode and cathode in the pattern of PNPN. Though it has multiple junctions, it is termed a diode for being a two-terminal device. The Shockley diode remains in an OFF state, with a very high resistance, until a voltage greater than the trigger voltage is applied across its terminals. When the voltage exceeds the trigger value, the resistance drops to an extremely low value and the device switches ON. The constituent

transistors upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...

help in maintaining the ON and OFF states. As the construction resembles a pair of interconnected bipolar transistors, one PNP and other NPN, neither transistor can turn ON until the other is turned ON due to the absence of any current through the base-emitter junction. Once sufficient voltage is applied and one of the transistors breaks down, it starts conducting and allows base current to flow through the other transistor, resulting in saturation of both the transistors, keeping both in ON state. On reducing the voltage to a sufficiently low level, the current flowing becomes insufficient to maintain the transistor bias. Due to insufficient current, one of the transistors will cut off, interrupting the base current to the other transistor, hence sealing both transistors in the OFF state.

Usages

Common applications: * Trigger switch for silicon controlled rectifier *

Relaxation oscillator In electronics a relaxation oscillator is a nonlinear electronic oscillator circuit that produces a nonsinusoidal repetitive output signal, such as a triangle wave or square wave. on Peter Millet'Tubebookswebsite The circuit consists of a feedb ...

/ sawtooth oscillator Niche applications: * Audio amplifier

Typical values

Dynistor

Small-signal Shockley diodes are no longer manufactured, but the unidirectional thyristor breakover diode, also known as the dynistor, is a functionally equivalent power device. An early publication about dynistors was published in 1958. In 1988 the first dynistor using

silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal s ...

was made. Dynistors can be used as switches in micro- and nanosecond power pulse generators.

References

* Michael Riordan and Lillian Hoddeson; ''Crystal Fire: The Invention of the Transistor and the Birth of the Information Age''. New York: Norton (1997) pbk.

External links

Shockley diode analysis

Transistor Diodes, by Shockley himself (Jan. 1960)
Diodes Solid state switches {{Electronics-stub