Shockley Diode – Working and Its Applications

Shockley diodes are four-layer PNPN semiconductor devices. It is a two-terminal device that’s why it is characterized as a diode.

These diodes are used primarily for switching applications as they can only perform the “ON” or “OFF” function thus, they are classified as a thyristor.
This diode was the early invention in thyristor class and was invented by William Bradford Shockley.

Constructions of Shockley Diode

The construction of the diode can be done by connecting 4-layers to form a PNPN junction.
The equivalent circuit of this diode using two transistors is shown in the above figure where the collector of a transistor T1 is connected to the base of T2.
The junction J1 is formed at the emitter-base junction of T1, J2 is at a common connected base-collector junction between T1 and T2,and the J3 is at the base-emitter junction of T2.
Therefore, as the base-emitter junctions, J1 and J3 must be forward biased and as a collector base junction, J2 must be reversely biased for linear operation.

As discussed above, these diodes consist of three junctions J1, J2, and J3. When the voltage is applied to this diode in such a way that the anode is made positive concerning the cathode, junctions J1 and J3 are forward biased and J2 is reverse biased.
When the diode is to be operated in forward biasing then J1 and J3 are forward biased and junction J2 is reverse biased. The Shockley diode is operated in forward-biased mode only.
When J1 and J3 are reversed biased and J2 is forward biased the devices start operating in reversed biased mode. But when it is operated in reverse biased and the voltage exceeds the breakdown voltage the diode gets damaged. So this diode is operated in forwarding biased mode only.

Reverse voltage can be blocked easily.
It can be protected by a fuse from over current.
These diodes have a high switching speed.
It gets latched into the on-state.
It can perform more as compared to a transistor because its construction includes two transistors that are connected through a common terminal.
Forward voltage drop is low so power dissipation is also low.

It cannot control at a fast speed.
Not simple to turn OFF.
There is no control above the forward breakdown voltage.
It conducts only in a single direction.
Its construction is somewhat difficult because it uses four semiconductor material layers.
It can switch ON suddenly because of the rate effect.
It doesn’t include any controlling terminal.

This diode can be used as a trigger switch within the circuits to switch ON an SCR.
It can be used in relaxation oscillators.