Vacancies and interstitials in indium nitride: Vacancy clustering and molecular bondlike formation from first principles X. M. Duan and C. Stampfl School of Physics, The University of Sydney, Sydney, New South Wales 2006, Australia Received 5 March 2009; published 8 May 2009 We investigate the structural and electronic properties and formation energies of vacancy, interstitial, and antisite defects, as well as complex formation, in wurtzite InN using first-principles calculations. The N interstitial, which forms a split-interstitial configuration with a N 2 -like bonding, has the lowest formation energy under N-rich conditions in p-type material, where it is a triple donor. We find that indium vacancies have a tendency to form “clusters,” which results in local nitrogen-rich regions and the formation of N x -molecular-like bonds. These complexes are amphoteric, have a relatively high formation energy, and are formed more readily under N-rich conditions. The nitrogen vacancy is a low energy defect under more In-rich conditions, and in p-type material it acts as a single and triple donor. In the neutral and negative charge states, we find nitrogen vacancies also prefer to be situated close to one another and to cluster, giving rise to local In-rich regions with electron localization at these metalliclike bonding configurations. The indium antisite in the 4+ charge state is the lowest-energy defect under In-rich conditions in p-type material and thus also acts as a donor. Our findings shed light on, and help explain, recent and sometimes conflicting, experimental observations. DOI: 10.1103/PhysRevB.79.174202 PACS numbers: 71.15.Nc, 71.55.-i, 71.15.Mb I. INTRODUCTION The group III nitrides GaN, AlN, and InN have attracted growing technical and scientific interest due to their applica- tions in, e.g., short-wavelength optoelectronic devices, such as light-emitting diodes and lasers. 1–3 Indium nitride is also of interest in relation to other technological applications such as solar cells and optical wave guides. 4,5 Moreover, recent studies show that InN and other III nitrides are promising materials for high-speed electronics and terahertz devices. 6,7 Compared to GaN and AlN, the physical properties of InN Refs. 8 and 9 are much less well established, largely due to the difficulties in synthesizing high quality single crystals. Only recently these problem have been overcome, 10 but key parameters still have not been conclusively determined. For example, a controversial issue is the value of the band gap: it has been long accepted as 1.9 eV but more recent experiments 11,12 and first-principles calculations 13–17 support a significantly lower value of around 0.7–0.8 eV, although some recent experiments 18 reported a somewhat larger value of 1.4 eV. The discrepancies in earlier reported band gaps which range from 0.65 to 2.3 eV may be due to poor material quality, i.e., nonstoichiometries, defects, and impurities, 19–22 which could form more readily due to the low thermal stability of InN. 23 Grown InN films are highly n type, which has been attributed to impurities O N and Si In  Ref. 24 and native point defects the nitrogen vacancy. 25,26 For the advancement of technological applications that utilize InN, it is important to have a deeper understanding of the behavior, role, and effect that defects and their complexes have on the atomic and electronic structure. Such knowledge is crucial to control the material properties and, ultimately, the device characteristics. There has been a first-principles investigation of point defects and impurities O, Si, and Mg in zinc blende zb InN Ref. 24 using density-functional theory DFT and the local density approximation LDA, as well as including self-consistent self-interaction and relax- ation corrections. This study found that the N vacancy is the lowest-energy native defect and that it is a donor in more p-type material. The Si and O impurities are very low energy defects and are also donors, possibly contributing to the high n-type background in grown material. The In vacancy and the Mg dopant were found to be triple and single acceptors, respectively. But due to the smaller band gap of InN com- pared to GaN and AlN, unlike the latter two compounds, these two defects remain relatively high in energy in InN. In the present paper, we investigate the atomic and elec- tronic properties, as well as associated formation energies, of native point defects and complexes in wz InN through ab initio calculations. We identify a number of interesting phe- nomena: first, “surprisingly,” we find that the indium vacan- cies and nitrogen interstitial introduce magnetism, where the value of the spin depends on the charge states. Second, we find that indium vacancies have a tendency to form “clus- ters” resulting in the formation of N x -molecular-like bonds, and third the N interstitial results in the formation of a N 2 -like-molecular bond “N-split-interstitial” configuration and has the lowest formation energy in the 3+ charge state under N-rich conditions in p-type material. Finally, the in- dium antisite, in the 4+ charge state, is the lowest-energy defect under In-rich conditions and in p-type material. As reported in detail elsewhere, 27 we also found that the N va- cancies in the neutral and negative charge states prefer to be located close to one another, i.e., to “cluster together”, giv- ing rise to a locally In-rich region. All these findings shed significant light on the behavior of native defects and com- plexes in indium nitride. The paper is organized as follows: in Sec. II, we describe the calculation method, and Sec. III reports results for native defects and their complexes. Sec. IV contains a discussion of our findings in light of experi- mental results, and Sec. V contains the conclusions. PHYSICAL REVIEW B 79, 174202 2009 1098-0121/2009/7917/1742029 ©2009 The American Physical Society 174202-1