[PDF] Shockley Diode | Construction | Working | Applications | New Topic [2023]

In this note, we will discussing about the Shockley Diode and its Construction, Working Principle, and Applications also. Welcome to Poly Notes Hub, a leading site for Diploma Engineering Notes Syllabus-Wise.

Author Name: Arun Paul.

What is Shockley Diode ?

A Shockley diode, also known as a p-n-p-n diode or a four-layer diode, is a semiconductor device that consists of four alternating layers of p-type and n-type semiconductor materials. This diode is a type of thyristor, a four-layer semiconductor device with three terminals: anode, cathode, and gate.

It operates using a phenomenon called “Negative Resistance” in which, once triggered into conduction, it continues to conduct even after the triggering voltage is removed until the current through it drops below a certain threshold.

Construction

Below we discuss about the construction of Shockley Diode –

Named after its inventor, a Shockley diode is a PNPN device having two terminals as shown in Fig(i). This device acts as a switch, consisting of four alternate P-type and N-type layers in a single crystal. The various layers as labeled as P1, N1, P2, and N2 for indentification. Since a P- region adjacent to an N- region may be considered a junction diode, the Shockley diode is equivalent to the junction diodes connected in series as shown in Fig(ii). The symbol of this diode is shown in Fig(iii).

Working Principle

The working principle of Shockley Diode is given below –

1. When the diode is forward-biased, diodes D1 and D3 would be forward-biased while diode D2 would be reverse-biased. Since diode D2 offers very high resistance and the three diodes are in series, then this diode presents a very high resistance. As the forward voltage increases, the reverse bias across D2 is also increased. At some forward voltage, a reverse breakdown of D2 occurs. Since this breakdown reduces resistance, the Shockley diode presents a very low resistance. From now on, this diode behaves as a conventional forward-biased diode; the applied voltage and external load resistance determine the forward current.
2. When the diode is reverse-biased, diodes D1 and D3 would be reverse-biased while diode D2 would be forward-biased. If the reverse voltage increases sufficiently, the reverse voltage breakdown of the Shockley diode is reached. At this point, diodes D1 and D3 would go into reverse voltage breakdown, the reverse current flowing through them would rise rapidly and the heat produced by this current flow could ruin the entire device. For this reason, the diode should never be operated with a reverse voltage sufficient to reach the reverse voltage breakdown point.

Applications

The applications of Shockley Diode are –

1. Used in Power Regulators.
2. Used in Switching Circuit.
3. Used in Pulse Generators.