| Group III nitrides have become materials of choice in the manufacturing of devices used in opto-electronic and high-temperature high-power electronic industries. Hence, these materials received wide attention and have become the focus of several theoretical and experimental studies. Though these materials are studied in bulk and thin film forms, research at the cluster level is still lacking. Hence, a first principles calculation, based on the Generalized Gradient Approximation (GGA) to Density Functional Theory (DFT) was initiated to study the structural and electronic properties of AlnN n, GanNn, and InnNn, (n = 1--6) clusters.; The calculated results show that the small polyatomic nitride clusters (monomer, triatomic and dimer) have a strong tendency to form N-N multiple bonds leading to the weakening of any existent metal-N or metal-metal bonds. In the absence of the N-N bonds, the metal-nitrogen bond dominates, forming short bond-lengths and large force constants. However, the strength of these heteronuclear bonds decreases in going from Al to Ga and In, whereas the weak metal-metal bond increases its strength from Al to Ga to In in the nitride clusters.; Starting from the trimers M3N3, a distinct structural difference between the lowest energy configurations of AlnNn and that of GanNn, and In nNn, clusters has been observed. For AlnNn, clusters, the metal-nitrogen bond is found to dominate the lowest energy configurations. As the cluster size is increased from Al3N3 to Al 6N6, a transition from planar ring structures towards a bulk-like three dimensional configurations is seen. However, in GanN n, and InnNn clusters, no such trend is observed and the lowest energy configurations are dominated either by N2 or (N3)- sub-units. The segregation of N atoms within the stoichiometric clusters indicates the possibility of N2 and N3 based defects in the thin-film deposition process which may affect the quality of the thin-film devices based on Group III nitrides. |
