First-principles density-functional theory was used to investigate the formation energies of defects and dopant complexes in wurtzite InN. Here, O substituted at a N site (ON) and Si substituted at an In site (SiIn) were the most favourable sites for O and Si. These acted as single donors, with the ionized state (ON+ and SiIn+) being most stable in p-type InN. Substitutional C on a N site (CN) and Mg on an In site (MgIn) were the most favourable sites for C and Mg, and were predicted to be single acceptors under more n-type conditions. Two O, Si and Mg atoms in the neutral or charged state preferred to be well-separated, with a mutual repulsion, as did two C atoms in the charged state. Two C atoms in the neutral state preferred to be located on neighbouring anion sites. Defect complexes of vacancies and impurities were investigated, plus defect configurations arising from so-called co-doping and/or cluster-doping: e.g. MgmOn (m, n ≤ 4) and SiiCj (i, j ≤ 4). Rather than being isolated, the nitrogen vacancy VN preferred to be bound to MgIn, forming a neutral MgInVN complex, while the In vacancy VIn preferred to bond to O, but the formation energy of ONVIn (in all charge states) was high. The formation energy of 3ONVIn was significantly lower, but was too high to be an important equilibrium defect. The results indicated that MgmOn could be important under In-rich and N-rich conditions: for p-type material, donor defects containing more O than Mg had very low formation energies while, in n-type material, acceptor defects containing more Mg than O had low formation energies. The complexes could provide more efficient p- (or n-) type doping than could single Mg (or single Si and O). The results suggested that complexes of SiiCj offered no advantage over single dopants.

Defect Complexes and Cluster Doping of InN - First-Principles Investigations. X.M.Duan, C.Stampfl: Physical Review B, 2009, 79[3], 035207