When an input signal reduces the effective channel width/charge in a field-effect transistor, what is this process called?

Introduction / Context:
FET operation can be described by two complementary mechanisms: enhancement (increasing channel carriers) and depletion (reducing channel carriers). Recognizing which mechanism is in play helps in understanding transfer curves and biasing strategies for JFETs and MOSFETs.

Given Data / Assumptions:

• Input voltage causes the conductive channel to become narrower (fewer carriers).
• We seek the correct terminology for this behavior.

Concept / Approach:
When the gate voltage drives the channel toward fewer carriers (for n-channel, a more negative VGS), the channel cross-section shrinks and resistance increases; this is depletion. Conversely, when the gate voltage attracts additional carriers and enlarges the channel (or creates an inversion channel in MOSFETs), that is enhancement.

Step-by-Step Solution:
Observe that the channel size decreases under the applied input.Link decreased carriers/width to increased depletion region.Name the mechanism accordingly: depletion.

Verification / Alternative check:
JFETs are depletion-mode by nature: applying reverse gate bias depletes the channel until cutoff at VGS(off). MOSFETs may operate in depletion or enhancement modes depending on structure; the language consistently uses “depletion” for reduced channel carriers.

Why Other Options Are Wrong:

• Enhancement: The opposite effect—adding carriers and increasing channel conduction.
• Substrate connecting: A layout/connection detail, not a conduction mechanism.
• Gate charge: Refers to charging the gate capacitances, not the channel depletion process.

Common Pitfalls:

• Confusing depletion in JFETs (reverse bias) with enhancement in E-MOSFETs (positive VGS for n-channel).
• Assuming “gate charge” dictates conduction; it mainly affects switching speed, not the steady-state mechanism naming.

Final Answer:
depletion