Comparative study of catalyst-induced doping and metal incorporation in silicon nanowires

Abstract

Foreign atoms incorporated into the crystal structure of a semiconductor have profound effects on the electronic structure and charge transport in the material, particularly in nanoscale systems. Here, we demonstrate that catalyst-induced doping of silicon nanowires (SiNWs) can be used as an effective way for controlling dopant density and electrical conductivity in SiNWs, allowing the construction of p-n junctions. We investigate and compare metal incorporation and charge transport in SiNWs grown by six different metal catalysts (In, Sn, Bi, Ga, Pb, and Au) in plasma-enhanced chemical vapor deposition. The distribution of the catalytic metals within SiNWs was mapped by scanning transmission electron microscopy using high-angle annular dark-field imaging. The metals are either homogenously distributed or segregated in clusters on the surface or in the core of the nanowires, depending on the metal catalyst used. Each of the metal catalysts is found to play a unique role in the charge transport of SiNWs. Sn, Pb, and Au yield semiconducting SiNWs, Ga and In produce p-type self-doped SiNWs, and Bi catalyzes n-type self-doped SiNWs. A combination of these different nanowires may provide a bottom-up growth strategy for fabrication of different nanowire-based electronic components.

Nanowire Growth without Catalysts: Applications and Mechanisms at the Atomic Scale

“…79 Alternative catalytic metals, including In, Sn, Bi, Ga, and Pb, were also examined, aiming primarily to lower the synthesis price; however these metals also penetrate inside nanowires during the growth. Significant modification in the charge transport was observed in Si 80 and Ge 81,82 nanowires. Si nanowires are also susceptible to incorporation and redistribution of impurities into silicon nanowires during In and Sn particle assisted growth.…”

Metastable Group IV Allotropes and Solid Solutions: Nanoparticles and Nanowires

“…Thus, an accurate characterization of the material is essential to gain information concerning the growth mechanism. Furthermore, segregation of heteroatoms at grain/twin boundaries 374 and incorporation of clusters in the Si NW matrix 375,376 must be excluded to confirm the formation of a solid solution. Several metal seeds have been applied as growth promoter for Si NWs including Ag, 377,378 Al, 379−384 Au, 220,385−387 Bi, 307,388,389 Co, 390 Cu, 3 1 0 , 3 8 6 , 3 9 1 Dy, 3 9 2 Fe, 3 9 2 , 3 9 3 Ga, 3 9 4 − 3 9 7 Gd, 3 9 8 In, 380,394,399,400 Mn, 398 Ni, 220,378,401,402 Pb, 374,378 Pd, 363 Pt, 375,403 Sn, 166,404−406 Ti, 407,408 Zn, 409,410 and binary alloys 241,388,411−414 of these elements.…”

“…Furthermore, segregation of heteroatoms at grain/twin boundaries 374 and incorporation of clusters in the Si NW matrix 375,376 must be excluded to confirm the formation of a solid solution. Several metal seeds have been applied as growth promoter for Si NWs including Ag, 377,378 Al, 379−384 Au, 220,385−387 Bi, 307,388,389 Co, 390 Cu, 3 1 0 , 3 8 6 , 3 9 1 Dy, 3 9 2 Fe, 3 9 2 , 3 9 3 Ga, 3 9 4 − 3 9 7 Gd, 3 9 8 In, 380,394,399,400 Mn, 398 Ni, 220,378,401,402 Pb, 374,378 Pd, 363 Pt, 375,403 Sn, 166,404−406 Ti, 407,408 Zn, 409,410 and binary alloys 241,388,411−414 of these elements. 347 Among these metal seeds, only a few examples exist that facilitate the VLS/SLS growth of Si NWs and simultaneously lead to hyperdoping of the Si crystal (Table 2).…”

“…Reports describing surface accumulation and clustering without any sign of homogeneous incorporation or proper determination of heteroatomic species in the Si lattice are omitted, even though conductivities and electrical properties have been determined. 374 In other studies the incorporation of high amounts of metal atoms from the seed in the Si NW host lattice can be expected on the basis of follow-up papers describing successful incorporation, but metal incorporation has not been discussed and direct proof via quantitative characterization methods is missing in these reports. 379,389,396,397,416,425 The incorporation of Au in Si from the seed is also not mentioned in most reports, even though Au concentrations in Si NWs can be in the range of the solid solubility of ∼1 × 10 17 cm −3 (∼2 × 10 −4 atom %) 234 which is significant for the electronic performance since Au introduces deep-level traps.…”

Evolution of the chemical composition of Sn thin films heated during x-ray photoelectron spectroscopy

“…In developing countries, like South Africa, sunlight radiation of 4.5-6.5 kWh/m 2 is common in a single day and thus solar cells have been identied as major contributor towards its energy supply [2]. One-dimensional silicon nanowires (SiNWs) have been identied as an attractive candidate to improve on the performance and stability of rst and second generation solar cells, while reducing the material cost that reduces the overall cost [3,4]. SiNWs have excellent anti-reective properties, due to their broadband optical absorption by multiple scattering incidents, where its reectance can be reduced to less than 1% in the spectral range from 400-1000 nm.…”