Nitrogen vacancies in InN: Vacancy clustering and metallic bonding from first principles

Abstract

We perform first-principles density-functional theory calculations to investigate the structural and electronic properties and the formation energies of nitrogen vacancies in wurtzite InN. We report an extensive and systematic study of the favorable atomic and electronic configurations of up to six vacancies in large supercells. The isolated vacancy acts as a donor in a p-type material where there is very little interaction between the singly positive charged vacancies. Their spatial distribution is therefore predicted to be random arrangements of single defects. However, in more n-type materials, the neutral charge state becomes favored and we find that the vacancies then prefer to be situated close to one another on the nearest-neighbor ͑like species͒ sites, forming "vacancy complexes or clusters." In the highest positive charge state of the complexes, the clustering is unstable with respect to isolated single positive charged vacancies. However, the negatively charged and lower positively charged ͑e.g., 1+ and 2+ charge states for three nitrogen vacancies͒ complexes also exhibit an attractive interaction between the vacancies, thus also favoring clustering. The formation of such nitrogen vacancy clusters gives rise to local indium-rich regions with metallic-like bonding. We discuss the effect that these defect structures have on the nature of the electronic states in the region of the band gap, in relation to recent experimental results ͑as measured by, e.g., infrared photoluminescence, x-ray diffraction, and transmission electron microscopy͒.

Identifying vacancy complexes in compound semiconductors with positron annihilation spectroscopy: A case study of InN

“…Nevertheless, this may not account for larger complexes of several V N which possess a positive binding energy (compared to isolated V N ) according to recent firstprinciples calculations. 9 The increased open volume in these defects could in principle promote a localization of the positron density. Additionally, the V N complexes are assumed to adapt negative charge states for elevated Fermi-level positions which additionally support trapping.…”

“…[3][4][5][6][7] Among them, isolated and complexed In vacancies (V In ) and N vacancies (V N ) are expected to be the dominant intrinsic acceptors and donors, respectively, according to latest density functional theory calculations. [8][9][10][11][12] Nevertheless, unambiguous experimental evidence on their nature and characteristics is still relatively scarce. This is due to limitations stemming from intrinsic properties of InN, as well as challenges related to the growth of high-quality material.…”

Self-compensation in highly n-type InN

“…[11][12][13][14] This suggests that thermal equilibrium considerations might not be appropriate for estimating point defect concentrations in n-type InN, a material which is commonly grown at low temperatures. The formation of point defects during growth of InN is likely to be dominated by other mechanisms.…”

“…These might be formed by singly negatively charged V N and multiply negatively charged V N clusters which become increasingly favorable at high Fermi levels. 14 Indirect evidence of the presence of V N clusters was found by the observation of V In -xV N complexes (x % 1-3) in positron measurements of the Si-doped InN samples. 20 The lower charge of the compensating V In -V N complexes in Si-doped samples and RTA treated irradiated layers, compared to the triply charged V In in the as-irradiated samples, might contribute to the observed mobility drop after annealing.…”

“…12 The identity of the shallow traps cannot be determined with our experiments. A comparison with DFT calculations 13,14 suggests negatively charged V À N and its complexes (xV ). The total acceptor concentrations estimated from Hall effect measurements are about 1-2 orders of magnitude higher than the values determined in temperature dependent Doppler broadening measurements.…”