Segregation mechanism of arsenic dopants at grain boundaries in silicon

Abstract

Three-dimensional distribution of arsenic (As) dopants at Σ3{111}, Σ9{221}, Σ9{114}, and Σ9{111}/{115} grain boundaries (GBs) in silicon (Si) is examined by correlative analytical methods using atom probe tomography (APT) combined with low-temperature focused ion beam (LT-FIB), scanning transmission electron microscopy, and ab initio calculations. Σ3{111} GBs, consisting of only 6-membered rings with small bond distortions, do not exhibit an apparent As segregation. Meanwhile, it is hypothesized that As atoms would segregate at 5-membered rings in the other GBs via anisotropic bond distortions spontaneously introduced so as to lower the donor level, as Jahn-Teller distortions. In addition, APT combined with LT-FIB suggests preferential As segregation around stretched $$\left\langle {1\overline 1 0} \right\rangle $$ bonds reconstructed in Σ9{114} and Σ9{111}/{115} GBs, that are inevitably introduced in the $$\left\langle {1\overline 1 0} \right\rangle $$ tilt GBs with the tilt angle larger than 70.5°. It is hypothesized that As atoms would form As dimers at stretched $$\left\langle {1\overline 1 0} \right\rangle $$ bonds and the adjacent $$\langle 111\rangle $$ bonds, due to the tendency of As with five valence electrons to form a three-coordinated configuration, which is efficiently attained by an As dimer of a long length. This work provides important insights into As segregation at GBs; it is mainly determined by electronic interactions depending on the characteristics of valence electrons of As atoms, as well as on local bond distortions at GBs, via anisotropic bond distortions and dimerization.

Keywords

• grain boundary segregation
• silicon
• coincident site lattice (csl)
• atom probe tomography (apt)
• ab initio calculations