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ABSTRACT: Here we report on the fabrication of high-density aligned Si nanotip arrays by chemical vapor deposition followed by dry oxidation
and an etching treatment. The dry oxidation investigations indicated that Al-catalyst particles located at the tip of Si nanocones
enhance their sharpening. This oxidation behavior is quite different from that of Au-catalyzed Si nanowires and is more favorable
to form very sharp Si nanotips. Field emission from an individual Si nanotip showed good field-emission characteristic with
a high emission current density of 1×104A/cm2 because of its sharp tip geography, suggesting their potential application for field emitters. Our work provides an effective
approach to fabricate high-density Si nanotip arrays, which overcomes some problems in the conventional fabrication approaches,
such as high cost, poor controllability, and complicated process.
Applied Physics A 04/2012; 99(4):705-709. · 1.63 Impact Factor
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ABSTRACT: We investigate shunting in a micromorph silicon tandem solar module using dark and illuminated lock-in thermography (DLIT and ILIT). Shunts are identified and quantified using DLIT. We then show how to isolate the layer causing the individual shunts by using white, blue, and infrared excitation spectra for the pulsed illumination in ILIT. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 03/2011; 8(4):1339 - 1341.
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ABSTRACT: Epitaxial silicon nanowires (NWs) of short heights (∼280 nm ) on Si <111> substrate were grown and doped in situ with boron on a concentration range of 10<sup>15</sup>–10<sup>19</sup> cm <sup>-3</sup> by coevaporation of atomic Si and B by molecular beam epitaxy. Transmission electron microscopy revealed a single-crystalline structure of the NWs. Electrical measurements of the individual NWs confirmed the doping. However, the low doped (10<sup>15</sup> cm <sup>-3</sup>) and medium doped ( 3×10<sup>16</sup> and 1×10<sup>17</sup> cm <sup>-3</sup> ) NWs were heavily depleted by the surface states while the high doped ( 10<sup>18</sup> and 10<sup>19</sup> cm <sup>-3</sup> ) ones showed volume conductivities expected for the corresponding intended doping levels.
Applied Physics Letters 07/2008; · 3.84 Impact Factor
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ABSTRACT: In the upper part of block-cast multicrystalline silicon one often finds silicon carbide and silicon nitride precipitates and inclusions. These contaminants can cause severe ohmic shunts in solar cells and thus decrease the efficiency of the solar cells very strongly. It is well known that the silicon carbide precipitates cause the ohmic shunts. However, the electrical properties of the silicon carbide was unknown so far. To study the electrical properties of these silicon carbide particles we isolated them from the silicon bulk material and performed different electrical measurements on them. The measurements show that the silicon carbide precipitates are highly conductive. An investigation of the heterojunction silicon–silicon carbide was also performed and a simulation of this heterojunction leads to a new model of the ohmic shunt mechanism. It is concluded that the shunt current flows inside of the filaments. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Physica Status Solidi (A) Applications and Materials 06/2007; 204(7):2190 - 2195. · 1.46 Impact Factor
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ABSTRACT: Single undoped Si nanowires were electrically characterized. The nanowires were grown by molecular-beam epitaxy on n+ silicon substrates and were contacted by platinum/iridium tips. I-V curves were measured and electron beam induced current investigations were performed on single nanowires. It was found that the nanowires have an apparent resistivity of 0.85 Ω cm, which is much smaller than expected for undoped Si nanowires. The conductance is explained by hopping conductivity at the Si–SiO2 interface of the nanowire surface.
Applied Physics Letters 01/2007; 90(1):012105-012105-3. · 3.84 Impact Factor
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ABSTRACT: The microstructure of SiC particles and SiC filament-type precipitates found in block-cast multicrystalline Si was studied in detail by transmission electron microscopy (TEM). TEM investigations showed that the SiC particles are monocrystalline and the SiC filaments are microcrystalline. Both types of precipitates consist of cubic SiC (3C polytype). However, a high density of planar defects was found in the filaments. High-resolution TEM analysis of the interface between SiC filaments and Si matrix revealed that the interface is rough and very wavy. SiC filaments do not show a special orientation relationship with respect to the Si matrix. The growth mechanisms of SiC precipitates are discussed. The influence of SiC inclusions in terms of device performance is also considered.
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ABSTRACT: In multicrystalline silicon solar cells linear shunts were found, which were caused by silicon carbide precipitates. These silicon carbide preciptitates have been isolated from the bulk material to investigate their electrical properties and to investigate the shunt mechanism. Current-voltage characteristics and four-point probe measurements were performed on the silicon carbide precipitates. In addition to the investigations on isolated silicon carbide preciptitates, current-voltage and capacitance-voltage characteristics were measured on precipitates, which were still embedded in the silicon bulk material. The results show that the silicon carbide precipitates are highly n-conductive, and a simulation of the shunt shows that the shunt current flows inside the silicon carbide material. Photoluminescence and cathodoluminescence measurements on the silicon carbide precipitates reveal that they emit green light and therefore should be detectable by luminescence methods.
