Band theory refresher: When an electron in a semiconductor gains sufficient energy to move from the valence band into the conduction band, what is the name of the effective positive charge left behind?

Introduction / Context:
Carrier concepts are central to semiconductor physics. Current in semiconductors can be described using two carrier types: electrons in the conduction band and holes in the valence band. Recognizing what happens when an electron transitions across the band gap is key to understanding diodes, BJTs, and CMOS devices.

Given Data / Assumptions:

• A crystalline semiconductor with distinct valence and conduction bands.
• An electron receives energy (thermal or optical) to cross the band gap.
• Lattice remains intact; we focus on electronic states.

Concept / Approach:
When an electron leaves a valence-band bond and enters the conduction band, it leaves behind an unoccupied state in the valence band. This vacancy behaves like a mobile positive charge known as a hole. Holes move through the lattice as neighboring electrons fill the vacancy, effectively transporting positive charge opposite to electron flow.

Step-by-Step Solution:

Verification / Alternative check:
Diode conduction can be modeled with electrons moving in the n-region and holes in the p-region. Device equations treat holes as legitimate carriers with their own mobility, validating the concept’s physical utility.

Why Other Options Are Wrong:

• Gap: Refers to the band gap energy, not the carrier.
• Vacancy/blank: Informal words; the standard technical term is hole.
• Exciton: A bound electron-hole pair, not the single positive carrier left behind.

Common Pitfalls:
Thinking holes are “real particles” like protons; they are quasiparticles representing the absence of an electron within the valence band.

Final Answer:
hole