Study of delta-doping using high-resolution RBS

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A delta-function-shaped Sb doping spike in Si is prepared by deposition of Sb on Si (00I) followed by low-temperature molecular beam epitaxy of Si. The depth profile of the Sb atoms is measured using high-resolution Rutherford backscattering spectroscopy, yielding a depth resolution of 0.3nm. The observed profile shows two peaks corresponding to the delta-doped layr (of width 0.5nm) and Sb atoms on the surface. The latter are due to surface segregation of Sb atoms during the growth of the Si cap-layr. the surface segregation rate is derived from the observed results at temperatures 70-280ﾟC, It is larger than the value extrapolated from high temperature (>400ﾟC) data by several orders of magnitude and shows a very weak temperature dependence as compared to the high temperature data. These features indicate a new surface segregation mechanism at low temperature. A possible mechanism for this anomalous segregation is "local heating" of surface atoms by the bonding energy released upon impact of Si atoms on the surface. In order to confirm the hypothesis of the local heating, Sb-delta-doped Si crystals were prepared at different growth rates. The observed Sb depth profiles are almost independent of the growth rate, strongly supporting the localheating hypothesis.