Group III impurities - Si interstitials interaction caused by ion irradiation

The off-lattice displacement of substitutional impurities (B, Ga) in Si caused by irradiation with energetic light ion beams has been investigated. Samples have been prepared by solid phase epitaxy (SPE) of pre-amorphized Si subsequently implanted with B and Ga at a concentration of about 1 x 10(20) at/cm(3) confined in a 300 nm thick surface region. The off-lattice displacement of the impurities was induced at room temperature (RT) by irradiation with high energy (> 600 keV) light ion beams (H, He) and detected by the channelling technique along different axes, using the B-11(p,alpha)Be-8 reaction and standard RBS, for B and Ga, respectively. The normalized channelling yield chi of the impurity signal increases with the ion fluence, indicating a progressive off-lattice displacement of the dopant during irradiation, until it saturates at chi(F) < 1 suggesting a non-random displacement of the dopant. Although the precise value of chi(F) depends on the channelling direction and dopant species, the off-lattice displacement rate, deduced from the chi versus interstitial fluence curve, only depends on the excess of Si self-interstitials (Si-I) generated by the irradiating beam through a parameter a that can be interpreted as an effective cross-section for the impurity-Si-I interaction. (c) 2005 Elsevier B.V. All rights reserved.