Relation between electrical activation and the B-induced strain in Si determined by reciprocal lattice mapping

Abstract

Boron-induced strain in Si epilayers was characterized by using high-resolution x-ray reciprocal lattice mapping. Samples grown by molecular beam epitaxy with high crystalline quality and full electrical activation of dopants with concentrations from 2*1019 cm-3 up to approximately=1*1021 cm-3 were employed, with measured lattice mismatches up to approximately=0.5% (tetragonal strain approximately=1%). The measured lattice contraction coefficient, beta , was (5.6+or-0.1)*10-24 cm3/atom, by considering the ratio of the lattice mismatch to the total dopant concentration. However, by considering only the effectively incorporated and activated dopant concentration, given by the measured carrier concentration, beta was found to be (6.3+or-0.1)*10-24 cm3/atom. Further measurements on B-doped structures grown at high temperatures (>or=600 degrees C), which had only partial electrical activation (<20%), confirmed that the B-induced lattice contraction in Si is related not to the total dopant concentration, but rather to the carrier concentration, which in principle corresponds to the active and substitutionally incorporated dopants. The high accuracy of our strain measurements was facilitated by the reciprocal lattice mapping method. In-plane and normal components (relative to the sample surface) of the lattice parameter of the epilayers were measured independently, and minute variations in the strain/relaxation status of the structures were accounted for.