Encoding Abrupt and Uniform Dopant Profiles in Vapor鈥揕iquid鈥揝olid Nanowires by Suppressing the Reservoir Effect of the Liquid Catalyst
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- 作者：Joseph D. Christesen ; Christopher W. Pinion ; Xing Zhang ; James R. McBride ; James F. Cahoon
- 刊名：ACS Nano
- 出版年：2014
- 出版时间：November 25, 2014
- 年：2014
- 卷：8
- 期：11
- 页码：11790-11798
- 全文大小：593K
- ISSN：1936-086X
文摘
Semiconductor nanowires (NWs) are often synthesized by the vapor鈥搇iquid鈥搒olid (VLS) mechanism, a process in which a liquid droplet鈥攕upplied with precursors in the vapor phase鈥攃atalyzes 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 鈥渞eservoir effect鈥?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 (鈮?50 nm/min) and low reactor pressures (鈮?0 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.