Lattice strain of B-B pairs formed by He irradiation in crystalline Si1-xBx/Si

This work reports on the lattice strain induced by small B clusters in Si produced by He irradiation of an epitaxial layer uniformly doped with substitutional B. By means of high resolution X-ray diffraction measurements and nuclear reaction analysis, lattice strain profiles and B lattice location of the sample before and after He irradiation were extracted, respectively. We found that, as a consequence of He irradiation, all B atoms form B-B pairs, and the tensile strain status of the as-grown B-doped layer lowers by a factor of about 2. Moreover, the volume lattice expansion Delta V per clustered B atom was found to be (-(10.0 +/- 0.6) angstrom(3)). This negative value of AV is very different from the positive one (+(3.7 +/- 0.6) angstrom(3)) found for B clusters created as a consequence of the B interaction with self-interstitials produced by Si implantation and subsequent annealing [G. Bisognin, D. De Salvador, E. Napolitani, A. Carnera, E. Bruno, S. Mirabella, F. Priolo, A. Mattoni, Semicond. Sci. Technol. 21 (2006) L41]. The opposite sign of this volume lattice expansion suggests that a strong correlation exists between the atomistic structures associated with these two types of complexes and the lattice strain that they induce in the Si lattice. (c) 2006 Elsevier B.V. All rights reserved.