Atomically smooth p-doped silicon nanowires catalyzed by aluminum at low temperature

Silicon nanowires (SiNWs) are powerful nanotechnological building blocks. To date, a variety of metals have been used to synthesize high-density epitaxial SiNWs through metal-catalyzed vapor phase epitaxy. Understanding the impact of the catalyst on the intrinsic properties of SiNWs is critical for precise manipulation of the emerging SiNW-based devices. Here we demonstrate that SiNWs synthesized at low-temperature by ultrahigh vacuum chemical vapor deposition using Al as a catalyst present distinct morphological properties. In particular, these nanowires are atomically smooth in contrast to rough {112}-type sidewalls characteristic of the intensively investigated Au-catalyzed SiNWs. We show that the stabilizing effect of Al plays the key role in the observed nanowire surface morphology. In fact, unlike Au which induces (111) and (113) facets on the nanowire sidewall surface, Al revokes the reconstruction along the [112] direction leading to equivalent adjacent step edges and flat surfaces. Our finding sets the lower limit of the Al surface density on the nanowire sidewalls at ∼2 atom/nm(2). Additionally, despite using temperatures of ca. 110-170 K below the eutectic point, we found that the incorporation of Al into the growing nanowires is sufficient to induce an effective p-type doping of SiNWs. These results demonstrate that the catalyst plays a crucial role is shaping the structural and electrical properties of SiNWs.