Room Temperature Boron Displacement in Crystalline Silicon induced by Proton Irradiation

The effect induced by proton irradiation on B-doped crystalline Si at room temperature is investigated in detail. The displacement of B atoms out of substitutional lattice sites is shown to be induced at room temperature by proton irradiation at energies ranging between 300 and 1300 keV This phenomenon was studied by means of channeling and nuclear reaction analysis techniques using the B-11(p, alpha)Be-8 nuclear reaction at 650. keV proton energy. For all the irradiation energies used, the fraction of displaced B atoms increases exponentially with proton irradiation fluence until saturation occurs. The B displacement rate strongly increases by decreasing the irradiation energy. We show that B off-lattice displacement is not due to a direct interaction of the proton beam with B atoms, but to the Si self-interstitials (I-Si) generated in the lattice by the irradiating beam. The displacement results from the formation of a mobile B-I-Si pair when a I-Si is trapped by a substitutional B. The measured damage rate has been interpreted in terms of the I-Si-B substitutional trapping probability and the resulting cross section at room temperature is (1.00 +/- 0.05) x 10(-16) cm(2).