Boron-interstitial clusters in crystalline silicon: stoichiometry and strain

In thiswork, we have investigated the strain induced in a Si crystal by Boron-interstitial clusters (BICs). BICs were formed by Si implantation and subsequent annealing of two Si samples, grown by molecular beam epitaxy (MBE), containing thin buried layers doped with different B concentrations (1E19 and 1E20 at./cm3). By B chemical profile diffusion analysis the doses of Si self-interstitials (Is) and Boron atoms trapped in the BICs were extracted. The B/I stoichiometric ratio is about 1 for the low B concentration and about 3.5 for the high B concentration sample. High-resolution X-ray diffraction (HRXRD) analyses provided a measure of the strain profile. While in the low B concentration sample, no appreciable strain was detected after BICs formation, at the higher B concentration, we found that the tensile strain present in the as-grown B doped layer changes to a strong compressive strain as a consequence of BIC formation. For this kind of clusters, the mean volume expansion with respect to the Si matrix is 29 ± 6 Å for each B atom trapped in the BICs.