What defines the concept of 'holes' in a semiconductor?

A hole in a semiconductor is defined as the absence of an electron in the valence band. In a semiconductor material, the valence band is the energy band where valence electrons reside. When these electrons gain enough energy (often from thermal excitation) to jump to the conduction band, they leave behind an empty state – a "hole."

This concept is essential because holes behave as positive charge carriers within the material. When we talk about electrical conduction in semiconductors, both the movement of electrons (negative charge carriers) and holes (positive charge carriers) contribute to the overall conductivity.

Understanding this concept is crucial for grasping how semiconductors function, particularly in devices like diodes and transistors where both types of charge carriers play vital roles in the operation of the device.