Role of Si self-interstitials on the electrical de-activation of B doped Si

The off-lattice displacement of B atoms in B-doped Si induced by the irradiation with light ion beam at room temperature has been investigated. A proton beam with energy ranging from 300 to 1300 keV was used to irradiate the single crystal Si samples containing a 400 nm thick surface layer (grown by molecular beam epitaxy) uniformly doped with B at a concentration of 1 x 10(20) B/cm(3). Channelling analyses along the < 100 > axis using the B-11(p,alpha)Be-8 reaction (at 650 keV proton energy) were used to detect the off-lattice displacements of B during irradiation. B is substitutional in the as-grown sample. During irradiation the normalized channelling yield of B chi(B) increases with the ion fluence and saturates at a value chi(F) smaller than unity, being this value independent of the energy of the irradiating beam. No change on the Si channelling yield was detected. The B displacement rate decreases with increasing the beam energy, it is controlled by the generation rate of Si self-interstitials, and it can be fitted by the following formula chi = chi(F) - [chi(F) - chi(0)] *exp(-sigma* N-I), where chi(0) is the chi of the non-irradiated sample, N-I is the fluence of the Si self-interstitials generated by the irradiating beam and sigma is a fitting parameter that accounts for the probability for a self-interstitial to be trapped by substitutional B. Displaced B is not randomly located in the lattice and channelling analyses indicate the formation of a B complex, mediated by B-i intersticialcy diffusion mechanism, partially displaced within the < 100 > channel. (c) 2005 Elsevier B.V. All rights reserved.