Transferred-Electron (Gunn) Devices: Relevant Time Constants Consider these time parameters in Gunn devices: (1) domain growth time constant, (2) transit time, (3) dielectric relaxation time in the positive mobility regime. Which of these are used in connection with transferred-electron device operation and design?

Introduction / Context:
Gunn diodes (transferred-electron devices) rely on formation and motion of high-field space-charge domains in materials like GaAs. Several characteristic times control whether domains form, how they evolve, and how they interact with external circuits.

Given Data / Assumptions:

• (1) Domain growth time constant: time for a nascent perturbation to grow into a mature domain.
• (2) Transit time: time for the domain to traverse the active region.
• (3) Dielectric relaxation time (positive mobility regime): time for charge perturbations to relax via conduction and permittivity.

Concept / Approach:

All three times are fundamental to TED physics. Dielectric relaxation competes with negative differential mobility; when relaxation is fast, perturbations dissipate instead of growing. The domain growth time sets how quickly a domain can form once the field exceeds threshold. Transit time links device length and oscillation frequency via domain formation and collapse at the anode.

Step-by-Step Solution:

Verification / Alternative check:

Device design charts relate length and doping to domain velocity and the transit-time-limited frequency, while relaxation and growth times determine operating regimes (domain vs LSA).

Why Other Options Are Wrong:

Omitting any one of these neglects a required piece of Gunn device dynamics and leads to incorrect regime prediction.

Common Pitfalls:

Confusing dielectric relaxation with recombination lifetime; equating transit time with period without considering domain dynamics.

Final Answer:

1, 2, and 3