Cross section of the interaction between substitutional B and Si self-interstitials generated by ion beams

The displacement of B from substitutional lattice sites during irradiation with a high energy (650 keV) proton beam is measured by channelling analyses along the < 100 > and < 110 > using the B-11(p, alpha)Be-8 reaction. The normalized B yield, X, increases with the ion fluence and saturates at a value (chi F < 1) that depends on the channelling axis, being minimum for channelling along (110). Therefore, displaced B is not randomly located in the lattice. The displacement rate is shown to be consistent with a model involving Si interstitial-B interaction and to depend on the local Si self-interstitial production rate, rather than long range interstitial migration. This was demonstrated by comparing results from samples with and without a Si layer containing 1 at.% C (known to be a trap for interstitial Si) interposed between the B doped layer and the substrate. The B displacement rate does not change in this sample indicating that self-interstitials produced at the end of the range do not play a role in this process. It is therefore concluded that only the Si interstitials produced in the B doped layer contribute to the B displacement and we can fit the damage rate with 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 and NI is the number of (Si interstitials) cm(-2) calculated by TRIM, with sigma similar to 10(-16) cm(2).