Carrier types in SCR anode current In a conducting SCR (thyristor), the anode current consists of which charge carriers?

Introduction / Context:
An SCR is a four-layer PNPN device. When it conducts, the internal conductivity is enhanced (conductivity modulation) due to high-level injection, and both types of carriers participate in current transport. Knowing this clarifies why the on-state voltage is low despite relatively thick silicon needed for blocking capability.

Given Data / Assumptions:

• SCR operating in its forward-conducting state.
• Charge transport through PN junctions within a multilayer device.
• High-level injection conditions.

Concept / Approach:

In the on-state, both P-type and N-type regions inject minority carriers into adjacent regions. The resulting carrier plasma reduces resistivity significantly (conductivity modulation). Consequently, anode current is carried by electrons and holes, much like in a forward-biased large-area diode but with regenerative thyristor action sustaining conduction.

Step-by-Step Solution:

Verification / Alternative check:

Two-transistor (PNP–NPN) equivalent model shows current sharing between transistor branches, implying both carrier types participate.

Why Other Options Are Wrong:

Options (a) and (b) are incomplete; (d) suggests exclusivity by operating quadrant, which does not apply to the on-state of an SCR; (e) is impossible for conduction.

Common Pitfalls:

Assuming a unipolar conduction similar to metals; neglecting the role of conductivity modulation in reducing on-state drop.

Final Answer:

Both electrons and holes