Gunn Diode Fundamentals: Assertion–Reason Assertion (A): A Gunn diode is a transferred-electron device. Reason (R): A Gunn oscillator exploits the transferred-electron effect to generate microwave oscillations.

Introduction / Context:
Gunn diodes are widely used microwave sources in the centimeter/millimeter bands. Their physics is fundamentally different from ordinary pn diodes because the effect arises from bulk transport in certain semiconductors.

Given Data / Assumptions:

• Material has multiple valleys in its conduction band (e.g., GaAs, InP).
• Under appropriate electric fields, electrons transfer to a higher-mass satellite valley.
• Negative differential mobility/negative differential resistance can occur.

Concept / Approach:

The transferred-electron effect shifts carriers from a low-mass, high-mobility valley to a high-mass, lower-mobility valley when the electric field exceeds a threshold. This reduces drift velocity with increasing field, creating negative differential resistance that supports oscillation. A Gunn “diode” has no pn junction; oscillation comes from domain formation in the bulk and interaction with an external resonant circuit or cavity.

Step-by-Step Solution:

Verification / Alternative check:

V–E (velocity–field) characteristics for GaAs show a peak then a decline, confirming negative differential mobility consistent with the transferred-electron effect.

Why Other Options Are Wrong:

Any option denying A or R conflicts with established device physics; saying R does not explain A ignores the direct link between the effect and the device category.

Common Pitfalls:

Assuming a pn junction exists; conflating tunnel diodes (quantum tunneling) with Gunn diodes (bulk transferred-electron effect).

Final Answer:

Both A and R are correct and R is correct explanation of A