Energetics of Boron in the Si(111)-($\sqrt{3}\times \sqrt{3}$)-B Surface Phase and in Subsurface Silicon Layers

The energetics of the boron substitution in the B/Si(111)-(root 3 x root 3) surface phase and in subsurface silicon layers has been studied using the semiempirical cluster method AM1. It has been found that the boron energy in the second layer (the B-S-5 site) is about 1 eV lower than in the adatom position (the B-T-4 site) and about 2 eV lower than in the fourth bulklike layer. The latter value may be interpreted as the surface segregation energy (enthalpy). The barrier height for the B-T-4-B-S-5 transfer has been found to be about 0.7 eV.