Bandgap
The magnitude of the coulombic potential determines the bandgap of a material, and the size of atoms and electronegativities are two factors that determine the bandgap. Materials with small atoms and strong, electronegative atomic bonds are associated with wide bandgaps. Smaller lattice spacing results in a higher perturbing potential of neighbors.
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.
Bandgaps can often be engineered by alloying, and Vegard's Law states that there is a linear relation between lattice constant and composition of a solid solution at constant temperature.
The position of the conduction band minima versus maxima in the band diagram determine whether a bandgap is direct or indirect. Most wide bandgap materials are associated with a direct bandgap, with SiC and GaP as exceptions.
Read more about this topic: Wide Bandgap Semiconductors, Material Properties