Study of delta-doping using high-resolution RBS

通过在Si(00I)衬底上沉积Sb，然后用低温分子束外延的方法，在Si中制备了一种三角函数形的Sb掺杂尖峰。用高分辨率卢瑟福背散射光谱测量了Sb原子的深度分布，深度分辨率为0.3 nm。观察到两个峰对应于表面上的Sb原子和β掺杂的LayR(宽度0.5 nm)。后者是由于硅帽层生长过程中Sb原子的表面偏析所致。表面偏析速率是从70-280ﾟC温度范围内的观测结果得到的，它比由高温(&gt；400ﾟC)数据外推得的值大几个数量级，与高温数据相比显示出很弱的温度依赖性。这些特征表明，低温下存在一种新的表面偏析机制。这种反常偏析的一种可能机制是硅原子撞击表面时释放的成键能使表面原子“局部加热”。为了验证局部加热假说，我们以不同的生长速率制备了掺Sb-Delta的硅单晶。观测到的Sb深度分布几乎与生长速率无关，有力地支持了局域加热假说。

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.