The lattice positions of B were determined, as a function of the B concentration, in very highly doped (001) layers which had been grown by means of gas-source molecular beam epitaxy. At concentrations of up to 2.5 x 1020/cm3, all of the B atoms resided on tetrahedrally bonded electrically active substitutional Si sites. At higher concentrations, inactive B was incorporated as B pairs which were located on single Si sites and were oriented mainly along in-plane [100] and [010] directions. The B pairs were sp2-bonded, with trigonal coordination, while substitutional single B atoms were sp3. A surface reaction path was proposed which led to inactive B incorporation.

Electrically Active and Inactive B Lattice Sites in Ultra-Highly B-Doped Si(001) - an X-Ray Near-Edge Absorption Fine-Structure and High-Resolution Diffraction Study A.Vailionis, G.Glass, P.Desjardins, D.G.Cahill, J.E.Greene: Physical Review Letters, 1999, 82[22], 4464-7