First-principles study of the self-interstitial diffusion mechanism in silicon

Abstract

We study the stability and migration mechanism of self-interstitials in Si through first-principles self-consistent pseudopotential calculations. The neutral Si interstitial is lowest in energy at a [110]-split site, with energy barriers of 0.15-0.18 eV for migrating into hexagonal and tetrahedral interstitial sites, while the migration barrier from a hexagonal site to a tetrahedral site is lower, 0.12 eV. These migration barriers are further reduced through successive changes in the charge state at different sites, which allow for the athermal diffusion of interstitials at very low temperatures. The [110]-split geometry is also the most stable structure for negatively charged states, while positively charged self-interstitials have the lowest energy at tetrahedral sites. Apart from the migration barrier, the formation energy of the [110]-split interstitial is estimated to be about 4.19 eV; thus, the resulting activation enthalpy of about 4.25 eV is in good agreement with high-temperature experimental data.

First-principles calculations of interstitial boron in silicon

“…In n-type material the pair is in the 1Ϫ charge state and the effective charge of the Si interstitial is neutral. These charge states of the Si interstitial are in agreement with first-principles calculations 26 for isolated Si interstitials. According to those calculations for interstitial Si the 1ϩ charge state is not stable for any Fermi level position.…”

“…A similar explanation has been given for the stability of the Si i (T 2ϩ ) defect. 26 The hexagonal H site is higher in energy by ϳ0.2 eV compared to the S configuration. The ionization level e (1ϩ/0) of H is at about E v ϩ0.10 eV.…”

“…According to them charge-assisted migration of B occurs through trapping of two electrons and holes. Charge-assisted migration has been proposed by Lee et al 26 also for Si self-interstitials. However, extensive studies of the migrational barriers should be performed to complete the picture.…”

“…The T 2ϩ defect ͑Si at the tetrahedral-interstitial site͒ is the ground state in p-type material, and the T 0 defect is a metastable configuration in n-type material. The comparison between B Si -Si i and Si i can be also made with re- 26 the Si i 2ϩ (T) and Si i 0 (X) defects are lowest-energy configurations for the isolated Si interstitials. T denotes the tetrahedral interstitial and X the ͗110͘-split configuration.…”

First-principles calculation of intrinsic defect formation volumes in silicon

“…Previous work by Zhu [31] and others [32] used the local density approximation (LDA), which does not include the gradient correction of GGA (generalized gradient approximation) methods such as PW91. GGA methods tend to predict energies of localized states (such as defects) with less error than LDA.…”