Semiconductor fundamentals: name the process when a free electron meets a hole What is the term for the event in which a conduction-band electron combines with a valence-band hole, eliminating both charge carriers?

Introduction / Context:
Carrier generation and recombination govern how diodes, transistors, and optoelectronic devices respond to bias, light, and temperature. Recognizing the correct terminology is foundational for analyzing semiconductor behavior.

Given Data / Assumptions:

• A “hole” is the absence of an electron in the valence band, behaving as a positive charge carrier.
• A “free electron” refers to a conduction-band electron.
• We refer to the microscopic event removing a carrier pair.

Concept / Approach:
When an electron drops from the conduction band to fill a hole in the valence band, the pair annihilates as mobile carriers. The energy released may emerge as phonons (nonradiative recombination) or as photons (radiative recombination), depending on material band structure and defects.

Step-by-Step Solution:
Identify the carriers: conduction electron and valence-band hole.Interaction: electron transitions to the valence band, filling the vacancy.Outcome: both carriers are removed from conduction; the process is called “recombination”.

Verification / Alternative check:
In LEDs and laser diodes, radiative recombination emits photons. In silicon devices, Shockley–Read–Hall centers facilitate nonradiative recombination via midgap states.

Why Other Options Are Wrong:
Covalent bonding: Describes static bonding in the lattice, not dynamic carrier loss. Thermal energy: Not a process name. Free electrons: A carrier type, not a process. Impact ionization: The reverse action that creates electron–hole pairs.

Common Pitfalls:
Confusing recombination with trapping (temporary immobilization) or with generation due to optical absorption.

Final Answer:
recombination