Leao C R, Fazzio A, da Silva Antonio J R
Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo, Brazil.
Nano Lett. 2008 Jul;8(7):1866-71. doi: 10.1021/nl080403d. Epub 2008 Jun 5.
Several experimental groups have achieved effective n- and p-type doping of silicon nanowires (SiNWs). However, theoretical analyses on ultrathin SiNWs suggest that dopants tend to segregate to their surfaces, where they would combine with defects such as dangling bonds (DB), becoming electronically inactive. Using fully ab initio calculations, we show that the differences in formation energies among surface and core substitutional sites decrease rapidly as the diameters of the wires increase, indicating that the dopants will be uniformly distributed. Moreover, occurrence of the electronically inactive impurity/DB complex rapidly becomes less frequent for NWs of larger diameters. We also show that the high confinement in the ultrathin SiNWs causes the impurity levels to be deeper than in the silicon bulk, but our results indicate that for NWs of diameters larger than approximately 3 nm the impurity levels recover bulk characteristics. Finally, we show that different surfaces will lead to different dopant properties in the gap.
几个实验组已经实现了硅纳米线（SiNWs）有效的n型和p型掺杂。然而，对超薄硅纳米线的理论分析表明，掺杂剂倾向于偏析到其表面，在那里它们会与诸如悬空键（DB）等缺陷结合，从而变得电中性。通过全从头计算，我们表明，随着纳米线直径的增加，表面和核心替代位点之间的形成能差异迅速减小，这表明掺杂剂将均匀分布。此外，对于较大直径的纳米线，电中性杂质/DB复合物的出现频率迅速降低。我们还表明，超薄硅纳米线中的高限制导致杂质能级比硅块体中的更深，但我们的结果表明，对于直径大于约3nm的纳米线，杂质能级恢复了块体特性。最后，我们表明不同的表面将导致能隙中不同的掺杂剂性质。
