Question

Silicon nitride has band gap energy of _______________eV.

Answer 1

In conductors, the valence band is either not fully occupied with electrons, or the filled valence band overlaps with the empty conduction band and as such there is no band gap between the valence band and conduction band.
In insulators the valence band is fully occupied with electrons due to the covalent bonds. To achieve conductivity, electrons from the valence band have to move into the conduction band and at the expense of considerable energy little conductivity may be achieved.
In semiconductors, there is a band gap, but compared to insulators it is so small (around 1-1.5 ev at 273 K) that even at room temperature electrons from the valence band can be lifted into the conduction band.
With band gap of 5 ev Silicon nitride is often used as an insulator .