Study of delta-doping using high-resolution RBS

通过在Si（00 I）上沉积Sb，然后低温分子束外延Si，在Si中制备δ函数形状的Sb掺杂尖峰。Sb原子的深度分布使用高分辨率卢瑟福背散射光谱测量，产生0.3nm的深度分辨率。观察到的轮廓显示出对应于δ掺杂层（宽度为0.5nm）和表面上的Sb原子的两个峰。后者是由于Si覆盖层生长过程中Sb原子的表面偏聚造成的。由70-280 ℃的观测结果导出了表面偏析率，它比由高温（>400 ℃）数据外推的值大几个数量级，并且与高温数据相比显示出很弱的温度依赖性。这些特征表明了一种新的低温表面偏析机制。这种异常偏析的一个可能的机制是“局部加热”的表面原子的Si原子的表面上的影响后释放的键能。为了证实局部加热的假设，在不同的生长速率下制备了Sb-δ掺杂的Si晶体。所观察到的Sb的深度分布几乎是独立的增长率，强烈支持localheating假说。

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.