Name the time parameter: The interval between the generation of a free electron–hole pair and its recombination in a semiconductor is called the ________.

Introduction / Context:
Carrier lifetime is a key figure of merit in semiconductors. It governs diffusion lengths, photoconductive gain, quantum efficiency, and transient response in devices such as photodiodes, LEDs, and bipolar transistors. Correct terminology helps connect physical understanding to equations used in design and analysis.

Given Data / Assumptions:

• A free electron–hole pair is created (e.g., by light absorption or injection).
• Recombination eventually annihilates the pair.
• We refer to the average time interval between creation and recombination.

Concept / Approach:

The average time a nonequilibrium carrier exists before recombining is called carrier lifetime (electron lifetime or hole lifetime; often minority-carrier lifetime). It is distinct from relaxation time (momentum-scattering time) and collision time (average time between scattering events), which impact mobility but not directly the recombination process duration.

Step-by-Step Solution:

Verification / Alternative check:

Device equations (Shockley–Read–Hall recombination) use lifetime τ as the characteristic time constant for carrier decay back to equilibrium after a perturbation.

Why Other Options Are Wrong:

• Relaxation time / collision time: relate to momentum randomization, not recombination.
• Lorentz time: not a standard semiconductor parameter.
• Transit time: time for carriers to traverse a device region, not recombination time.

Common Pitfalls:

Confusing mobility-related times with recombination lifetime; they influence different aspects of device behavior.

Final Answer:

Lifetime