Shockley diode structure How many semiconductor layers does a Shockley diode (two-terminal thyristor) contain?

Introduction / Context:
The Shockley diode is the simplest thyristor structure—a two-terminal, four-layer device that exhibits regenerative switching. It is foundational to understanding SCRs (which add a gate terminal for controlled turn-on).

Given Data / Assumptions:

• A Shockley diode is a PNPN device with two terminals (anode and cathode).
• Exhibits breakover behavior and negative resistance region.

Concept / Approach:

Its internal structure is equivalent to two interconnected bipolar transistors (pnp and npn). Regeneration occurs when combined current gains approach unity, causing rapid turn-on at the breakover voltage. The four alternating layers (PNPN) form three junctions J1, J2, and J3.

Step-by-Step Solution:

Verification / Alternative check:

Device symbols and equivalent transistor models confirm the four-layer architecture with two terminals.

Why Other Options Are Wrong:

• 2 or 3 layers cannot produce the characteristic thyristor breakover behavior.

Common Pitfalls:

Assuming “diode” implies two layers; the Shockley diode is a historical misnomer for a four-layer switch.

Final Answer:

4