Chemical bonding in group III nitrides

We analyze in this article the evolution of the chemical bonding in group III nitrides (MN, M = Al, Ga, In), from the N-N bond dominated small clusters to the M-N bond dominated crystals, with the aim of explaining how the strong multiple bond of N-2 is destabilized with the increase in coordination. The picture that emerges is that of a partially ionic bond in the solid state, which is also present in all the clusters. The covalent N-N bond, however, shows a gradual decrease of its strength due to the charge transfer from the metal atoms. Overall, Al clusters are more ionic than Ga and In clusters, and thus the N-N bond is weakest in them. The nitrogen atom charge is seen to be proportional to the metal coordination, being thus a bond-related property, and dependent on the M-N distance. This explains the behavior observed in previous investigations, and can be used as a guide in predicting the structures and defects on semiconductor quantum dot or thin film devices of these compounds.