Band theory concept check: When an electron is excited from the valence band to the conduction band, the vacancy left behind is called a:

Introduction / Context:
Carrier generation and recombination underpin semiconductor device action. When electrons gain sufficient energy to move to the conduction band, they leave vacancies that behave as positive charges. Recognizing the correct terminology is fundamental for understanding PN junctions, photodiodes, and intrinsic conductivity changes with temperature or illumination.

Given Data / Assumptions:

• Crystalline semiconductor with valence and conduction bands separated by a bandgap.
• Excitation can be thermal, optical, or electrical.
• Steady state after a single excitation event.

Concept / Approach:

Promotion of an electron to the conduction band leaves a missing electron in the valence band. This vacancy is termed a “hole” and behaves as a mobile positive charge carrier. Together, the excited electron and the hole constitute an electron-hole pair; recombination is the reverse process where they annihilate and release energy (often as heat or photons).

Step-by-Step Solution:

Verification / Alternative check:

Optical absorption in semiconductors and Hall effect measurements reveal contributions from both electrons and holes, validating the conceptual model.

Why Other Options Are Wrong:

• Energy gap: the bandgap itself, not the vacancy.
• Electron-hole pair: describes the pair, not specifically the vacancy.
• Recombination: the process by which the pair annihilates; it is not the vacancy name.
• Phonon: quantized lattice vibration, unrelated to the vacancy identity.

Common Pitfalls:

• Thinking a hole is a particle like a proton; it is an effective positive charge due to missing electron.
• Confusing carrier generation with doping; intrinsic generation creates electron-hole pairs without adding impurities.

Final Answer:

hole