How do temperature, light, and magnetic fields affect a semiconductor’s conductivity?

The conductivity of a semiconductor is significantly influenced by temperature, light, and magnetic fields, as these factors alter the concentration or movement of charge carriers.

Temperature

At low temperatures, electrons are bound in the crystal lattice, making semiconductors poor conductors. As temperature increases, thermal vibrations break covalent bonds, generating free electrons and holes that participate in conduction. While this increase in charge carriers generally enhances conductivity, it is important to note that carrier mobility—the speed at which these carriers move—typically decreases as temperature rises.12

Light

Light can increase conductivity through the internal photoelectric effect. When photons with energy greater than the material's energy gap strike the semiconductor, they excite electrons from the valence band to the conduction band. This process creates additional hole-electron pairs, which can substantially increase the material's electrical conductivity even under low levels of illumination.3

Magnetic Fields

When a semiconductor carrying an electric current is placed in a perpendicular magnetic field, it experiences the Hall effect. This phenomenon causes a transverse electric field to develop as moving charge carriers are deflected to one side of the material. The resulting Hall voltage can be used to measure carrier density and mobility, providing insight into the material's electrical properties.4