Band gap: definition · Chip Field Guide

Beginner

The jump in energy an electron in silicon must make to break free and move around. Until it makes the jump, it is stuck.

Novice

The range of energies with no allowed electron states, between the top of the valence band ( $E_{\mathrm{v}}$ ) and the bottom of the conduction band ( $E_{\mathrm{c}}$ ). In silicon $E_{\mathrm{g}} = 1.12\,\mathrm{eV}$ at room temperature.

Expert

$E_{\mathrm{g}}$ sets $n_{\mathrm{i}}$ through $n_{\mathrm{i}}^2 = N_{\mathrm{c}} N_{\mathrm{v}}\, e^{-E_{\mathrm{g}}/kT}$ , so it controls intrinsic carriers, junction leakage and the temperature at which doping stops mattering. Silicon’s gap is indirect, which is why it is a poor light emitter.