Polymorphous silicon nanowires synthesized by plasma-enhanced chemical vapor deposition
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Polymorphous silicon nanowires synthesized by plasma-enhanced chemical vapor deposition X.B.Zeng, X.B.Liao, H.W.Diao, Z.H.Hu, Y.Y.Xu, S.B.Zhang, C.Y.Chen, W.D.Chen, G.L.Kong State key Laboratory for surface physics, Institute of Semiconductors Chinese Academy of Science,Beijing,100083,China ABSTRACT Polymorphous Si nanowires (SiNWS) have been successfully synthesized on Si wafer by plasma enhanced chemical vapor deposition (PECVD) at 440oC,using silane as the Si source and Au as the catalyst. To grow the polymorphous SiNWS preannealing the Si substrate with Au film at 1100 oC is needed. The diameters of Si nanowires range from 15 to 100 nm. The structure ,morphology and chemical composition of the SiNWS have been characterized by high resolution x-ray diffraction, scanning electron microscopy, transmission electron microscopy, as well as energy dispersive x-ray spectroscopy. A few interesting nanowires with Au nanoclusters uniformly distributed in the body of the wire were also produced by this technique. INTRODUCTION Silicon nanowires (SiNWS) have attracted much attention[1-4] recently because of their possibility of testing fundamental concept of quantum physics and potential application in nanoelectronics. Much effort has been focused on the synthesis of SiNWS by Vapor-Liquid-Solid (VLS) growth[1,5-13], Solution-Liquid-Solid growth[2], Solid-Liquid-Solid growth[3,14,15] and other methods[16-19]. Among these approaches the most famous one is Vapor-Liquid-Solid growth. In the VLS growth a metal droplet acts as the energetically favored site for vapor-phase Si adsorption and when supersaturated the nucleation site for Si crystallization[7]. By Si precipitation from the droplet grow silicon nanowires. This paper demonstrates a new regime of VLS to prepare Si nanowires on Au covered Si (100) substrate, where Au-Si alloy droplets were formed by pre-annealing and the nanowires were grown by PECVD at a lower substrate temperature of 440oC.By combining pre-annealing with PECVD this technique could produce not only Si nanowires but also nanowires in which gold nanocluster evenly distributed. It is desirable to extend this approach to the controlled doping of nanowires [20,21] or the growth of nanowires superlattice [22] because PECVD can enable great chemical reactivity.
EXPERIMENT
Doped (ρ=2-4 cm) n-type Si(100) wafer was used as a substrate. The Si substrate was degreased in detergent and cleaned ultrasonically in ethanol in turns for 10 min, then the Si substrate was leached in deionized water and dry. The cleaned substrate was placed in a reaction
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chamber, and gold was evaporated on the Si surface at 200 in vacuum of 1 10-5 Torr. The thickness of gold deposited was estimated to be 0.5 nm. Subsequently, the specimen was transferred to a quartz tube and preannealed in nitrogen atmosphere at 1100 for 1 h. The substrate prepared in this way was placed in plasma enhanced vapor deposition(PECVD) chamber, which was evacuated to 1 10-5 Torr, then SiNWS were grown at 440 , with an rf power densi
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