Gunn devices and GaAs – Negative differential mobility statement Gallium arsenide (GaAs) is known for intervalley transfer under high electric field. State whether GaAs exhibits negative differential mobility (basis of the Gunn effect).

Introduction:
Negative differential mobility (NDM) occurs when carrier drift velocity decreases with increasing electric field beyond a threshold. In certain III-V semiconductors, such as GaAs, intervalley transfer moves electrons from a low-mass, high-mobility valley to a higher-mass, lower-mobility satellite valley, causing NDM and enabling Gunn oscillations.

Given Data / Assumptions:

• n-type GaAs under high electric fields (typically a few kV/cm).
• Room-temperature operation is of interest.
• Bulk transport dominated by intervalley transfer (Ridley–Watkins–Hilsum mechanism).

Concept / Approach:

As the electric field rises above threshold, electron population shifts to satellite valleys with larger effective mass. The average drift velocity peaks and then falls with further field increase, giving negative differential mobility (dv_d/dE < 0). Spatial domains form and drift across the sample, generating microwave oscillations without a traditional p-n junction.

Step-by-Step Solution:

Verification / Alternative check:

Velocity-field characteristics of GaAs show a peak near the threshold field followed by a decline, confirming NDM at room temperature in n-type material.

Why Other Options Are Wrong:

“False” contradicts well-known transport curves; limiting to <1 GHz or p-type is incorrect; cryogenic temperatures are not required for Gunn operation in GaAs.

Common Pitfalls:

Confusing negative differential resistance in tunnel diodes with NDM in bulk GaAs; overlooking the need for n-type doping and device length criteria.

Final Answer:

True.