Question

why is GaN has wide band gap compare with Si?

Answer 1

Silicon’s band gap is around 1.1 eV, whereas the GaN band gap is around 3.4 eV. wide-bandgap materials have bandgaps in the range of 2 - 4 eV

Gallium nitride (GaN) is a binary III/V direct bandgap semiconductor commonly used in light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure. Its wide band gap of 3.4 eV affords it special properties for applications in optoelectronic, high-power and high-frequency devices. The high value of the band gap (3.4 eV) is attributed to the high value of the bond strength which increases the band gap.

The size of the atoms and the number of protons in the atom are the primary predictors of the strength and layout of the bandgaps. Materials with small atoms and strong electronegative atomic bonds are associated with wide bandgaps. Elements high on the periodic table are more likely to be wide bandgap materials. With regard to III-V compounds, nitrides are associated with the largest bandgaps, and, in the II-VI family, oxides are generally considered to be insulators

so silicon is lower in the periodic table and nitride is high on the periodic table so it has wide band gap is high