Surface Charge Density of Unpassivated and Passivated Metal-Catalyzed Silicon Nanowires

Seo, Kang-Ill; Sharma, Shashank; Yasseri, Amir A.; Stewart, Donald C.; Kamins, Theodore I.

doi:10.1149/1.2159295

Cited by 116 publications

(107 citation statements)

References 9 publications

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“…Hence, the substantial change in transport properties can be associated with removal of the surface layer in the small diameter NWs. These diameter dependent results could arise from several factors, including (i) diameter-dependent dopant incorporation during growth, (ii) dielectric confinement (24,25), and (iii) surface depletion (26,27), although results indicate that (i) is the dominant factor. The dielectric confinement model predicts that dopant ionization energy will increase with decreasing NW diameter, which could deplete small diameter NWs.…”

Section: Resultsmentioning

confidence: 99%

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Diameter-dependent dopant location in silicon and germanium nanowires

Xie

Fang

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

108

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We report studies defining the diameter-dependent location of electrically active dopants in silicon (Si) and germanium (Ge) nanowires (NWs) prepared by nanocluster catalyzed vapor-liquidsolid (VLS) growth without measurable competing homogeneous decomposition and surface overcoating. The location of active dopants was assessed from electrical transport measurements before and after removal of controlled thicknesses of material from NW surfaces by low-temperature chemical oxidation and etching. These measurements show a well-defined transition from bulk-like to surface doping as the diameter is decreased <22-25 nm for nand p-type Si NWs, although the surface dopant concentration is also enriched in the larger diameter Si NWs. Similar diameterdependent results were also observed for n-type Ge NWs, suggesting that surface dopant segregation may be general for small diameter NWs synthesized by the VLS approach. Natural surface doping of small diameter semiconductor NWs is distinct from many top-down fabricated NWs, explains enhanced transport properties of these NWs and could yield robust properties in ultrasmall devices often dominated by random dopant fluctuations.nanoelectronics ͉ surface doping ͉ surface segregation ͉ vapor-liquid-solid growth

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Section: Resultsmentioning

confidence: 99%

“…Surface Depletion. Surface depletion is a general phenomenon expected in planar (34) and NW (26,27) devices because of states at the Si/SiO x interface that trap carriers. The thickness of the surface depletion layer is governed by the interface trap density and dopant/carrier concentration (26,34).…”

Section: Nw Surface Oxidation and Etchingmentioning

confidence: 99%

Diameter-dependent dopant location in silicon and germanium nanowires

Xie

Fang

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

108

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“…Experimental proof of this effect in semiconducting NWs was observed by photoconductivity or capacitancevoltage measurements. [7][8][9][10] In this letter, we present our results on the influence of surfaces on GaAs NWs measured by low temperature microphotoluminescence ͑-PL͒ spectroscopy. A systematic comparison is done between unpassivated NWs and those that were capped with a shell of Al 0.4 Ga 0.6 As.…”

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confidence: 99%

Impact of surfaces on the optical properties of GaAs nanowires

Demichel

Heiß

Bleuse

et al. 2010

Applied Physics Letters

221

231

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The effect of surfaces on the optical properties of GaAs nanowires is evidenced by comparing nanowires with or without an AlGaAs capping shell as a function of the diameter. We find that the optical properties of unpassivated nanowires are governed by Fermi-level pinning, whereas, the optical properties of passivated nanowires are mainly governed by surface recombinations. Finally, we measure a surface recombination velocity of 3 ϫ 10 3 cm s −1 one order of magnitude lower than values previously reported for ͕110͖ GaAs surfaces. These results will serve as guidance for the application of nanowires in solar cell and light emitting devices. © 2010 American Institute of Physics. ͓doi:10.1063/1.3519980͔Semiconducting nanowires ͑NWs͒ are a topic of intense research as they offer the opportunity to explore properties of one-dimensional electronic systems. The understanding and the mastering of the electronic properties of such onedimensional systems are essential to achieve high efficiency devices. In particular, with the increase of the surface/volume ratio, the electronic properties of NW based devices become strongly dependent on the surface electronic states that can alter their electronic properties. Two main surface effects are reported in literature: surface states can act as recombination centers for free carriers 1,2 or as surface charged traps. 3,4 The first effect has recently been quantified by an original optical method for silicon NWs. 5,6 The surface charge traps induce a pinning of the Fermi-level at the surface. A depletion shell appears and the electronic channel available for carriers is narrowed. Experimental proof of this effect in semiconducting NWs was observed by photoconductivity or capacitancevoltage measurements. [7][8][9][10] In this letter, we present our results on the influence of surfaces on GaAs NWs measured by low temperature microphotoluminescence ͑-PL͒ spectroscopy. A systematic comparison is done between unpassivated NWs and those that were capped with a shell of Al 0.4 Ga 0.6 As. Moreover, we take advantage of the tapered shape of the NWs to understand the role of diameter and surface/volume ratios in the luminescence efficiency. We demonstrate that capping directly modifies the recombination velocity and that passivated NW electronic properties are governed by surface recombinations, whereas, unpassivated NWs are strongly depleted by the Fermi-level pinning at the surface induced by charged surface trap states. This work will serve as a guidance for the passivation of the NW surfaces, which is of crucial importance for applications in laser and solar cell technology. 11GaAs NWs were synthesized by molecular beam epitaxy. The growth conditions are described elsewhere. 12-14The NWs have a prismatic shape and exhibit a pure zincblende GaAs crystal structure oriented along the ͑111͒ direction. Surfaces are ͕110͖ oriented. 15,16 The NWs are extremely long ͑16 m͒ and present a tapered shape ͑diameters go from 140 nm at the base to 70 nm at the tip͒. We investigated two samples which di...

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“…This is because of several issues such as nanowire size fl uctuations, which can affect bandgap and barrier heights, especially for ultra-scaled (sub-20 nm diameter) nanowires; 4,5 dopant fl uctuations, where a dopant concentration difference of only a few atoms signifi cantly alters the interface and wire size, affecting the bandgap; 6 and surface states that have been observed in Si nanowires covered with thermal oxides. 7,8 Despite these challenges, some nice work has been shown recently on single nanowire devices. For example, Woodruff et al fabricated Si nanowire diodes with Ni and Ni 2 Si contacts on n -type Si.…”

Section: Contacts To Nanowiresmentioning

confidence: 99%