Encoding Abrupt and Uniform Dopant Profiles in Vapor–Liquid–Solid Nanowires by Suppressing the Reservoir Effect of the Liquid Catalyst

Citations Over TimeTop 10% of 2014 papers

Abstract

Semiconductor nanowires (NWs) are often synthesized by the vapor-liquid-solid (VLS) mechanism, a process in which a liquid droplet-supplied with precursors in the vapor phase-catalyzes the growth of a solid, crystalline NW. By changing the supply of precursors, the NW composition can be altered as it grows to create axial heterostructures, which are applicable to a range of technologies. The abruptness of the heterojunction is mediated by the liquid catalyst, which can act as a reservoir of material and impose a lower limit on the junction width. Here, we demonstrate that this "reservoir effect" is not a fundamental limitation and can be suppressed by selection of specific VLS reaction conditions. For Au-catalyzed Si NWs doped with P, we evaluate dopant profiles under a variety of synthetic conditions using a combination of elemental imaging with energy-dispersive X-ray spectroscopy and dopant-dependent wet-chemical etching. We observe a diameter-dependent reservoir effect under most conditions. However, at sufficiently slow NW growth rates (≤250 nm/min) and low reactor pressures (≤40 Torr), the dopant profiles are diameter independent and radially uniform with abrupt, sub-10 nm axial transitions. A kinetic model of NW doping, including the microscopic processes of (1) P incorporation into the liquid catalyst, (2) P evaporation from the catalyst, and (3) P crystallization in the Si NW, quantitatively explains the results and shows that suppression of the reservoir effect can be achieved when P evaporation is much faster than P crystallization. We expect similar reaction conditions can be developed for other NW systems and will facilitate the development of NW-based technologies that require uniform and abrupt heterostructures.

Related Papers

• → Preparation and photoluminescence properties of amorphous silica nanowires(2001)170 cited
• → Fundamental Strategy for Creating VLS Grown TiO₂ Single Crystalline Nanowires(2012)32 cited
• → Real-Time Observation of Collector Droplet Oscillations during Growth of Straight Nanowires(2014)19 cited
• → B-doping of vapour–liquid–solid grown Au-catalysed and Al-catalysed Si nanowires: effects of B₂H₆gas during Si nanowire growth and B-doping by a post-synthesisin situplasma process(2007)29 cited
• Growth and characterisation of ZnSe semiconductor nanowires(2011)