- The bandgap (Eg) is the energy difference between the top of the valence band and the bottom of the conduction band in a material. Electrons need to gain energy at least equal to the bandgap to move from the valence band to the conduction band and become mobile charge carriers. - In good conductors (like metals), the valence band and conduction band either overlap or are very close, meaning the bandgap is essentially zero (Eg ≈ 0). Electrons are free to move. - In semiconductors, there is a small bandgap, typically ranging from about 0.1 eV to 3 eV. At room temperature, a small number of electrons have enough thermal energy to cross the bandgap, leading to moderate conductivity which increases with temperature. Examples: Silicon (Si) senide (GaAs) ≈ 1.4 eV. - In insulators, the bandgap is large, typically greater than 3 eV. Very few electrons have enough energy to jump across this large gap at room temperature, resulting in extremely low conductivity. Examples: Diamond ≈ 5.5 eV, Silicon Dioxide (SiO₂) ≈ 9 eV. - A bandgap of 5.0 eV falls into the range characteristic of insulators.