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Horizontal GaN nanowires grown on Si (111) substrate: the effect of catalyst migration and coalescence
摘要： Here, we demonstrate the growth of horizontal GaN NWs on silicon (111) by a surface-directed vapour–liquid–solid (SVLS) growth. The influence of the Au/Ni catalysts migration and coalescence on the growth of the NWs has been systematically studied. A 2-D root-like branched NWs were gown spontaneously through catalyst migration. Furthermore, a novel phenomenon that a catalyst particle is embedded in a horizontal NW was observed and attributed the destruction of growth steady state due to the catalysts coalescence. The transmission electron microscopy (TEM) and photoluminescence (PL), cathodoluminescence (CL) measurement demonstrated that the horizontal NWs exhibit single crystalline structures and good optical properties. Our work sheds light on the horizontal NWs growth and should facilitate the development of highly integrated III?V nanodevices on silicon.
关键词： GaN nanowires,silicon substrate,coalescence,catalyst migration,SVLS growth
更新于2025-09-23 15:21:21
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Growth mechanisms of F4-TCNQ on inorganic substrates and nanostructures
摘要： The organic semiconductor tetrafluorotetracyanoquinodimethane (F4-TCNQ) is a promising candidate for the doping of organic semiconductors, two-dimensional materials and inorganic compounds, such as ZnO, and also to enhance the charge carrier injection at contacts in organic electronics. In order to evaluate its applicability as a functionalization material or as an electrically active part in devices, we present a systematic study on the growth mode of F4-TCNQ beyond the first few monolayers on different inorganic substrates that cover a broad variety regarding their physical, chemical and morphological surface properties. The materials used are silicon, silicon carbide, graphene on silicon, sapphire, nanocrystalline diamond, as well as gallium nitride (GaN) layers and nanowire arrays. While the surface termination influences the shape and morphology of the islands of F4-TCNQ which form on all substrates investigated, no significant dependence of the growth mode on the substrate doping type and concentration is observed. GaN nanowires are found to act as nucleation sites for F4-TCNQ islands and to be covered by few monolayers of F4-TCNQ forming a closed coaxial shell. In conclusion, F4-TCNQ is identified to nucleate via Stranski-Krastanov growth consisting of monolayers and islands of different size and shape. The findings in this work provide basic growth information for the implementation of F4-TCNQ as functionalization material for nanowire-based applications.
关键词： GaN nanowires,surface functionalization,growth mode,organic semiconductors,organic electronics,surface doping,F4-TCNQ
更新于2025-09-23 15:21:01
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Hybrid P3HT: PCBM/GaN nanowire/Si cascade heterojunction for photovoltaic application
摘要： Poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) are commonly used for the fabrication of organic photovoltaics (OPV). Efficiency limitations of OPVs could be circumvented by incorporation of inorganic nanostructures into organic blends. Again, integration of organic solar cells with well-developed silicon photovoltaic technology is ultimately desirable. In the present work, GaN nanowires with diameters of 25–50 nm and two lengths (200 and 500 nm) have been grown using molecular beam epitaxy technique. Solar-grade monocrystalline silicon wafers were used as substrates for nanowire synthesis. GaN nanostructures were incorporated into P3HT:PCBM photoactive layer in order to facilitate charge transfer between P3HT:PCBM and Si. Samples with and without nanowires were compared. Addition of nanowires led to the improvement in photovoltaic performance. Open circuit voltage has risen by 72% and short circuit current density by 200%. Series resistance has decreased 50 times, and power conversion efficiency has risen 20.7 times. Additional maxima are found in photocurrent spectrum corresponding to carriers being generated near GaN absorption edge. Moreover, external quantum efficiency peaks near GaN absorption edge, indicating transfer channel via the formation of current P3HT/GaN/Si cascade heterojunction. Mechanism explaining source of abovementioned improvement is proposed.
关键词： Molecular beam epitaxy,Energy conversion,P3HT,Solar cells,PCBM,GaN nanowires
更新于2025-09-23 15:21:01
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Mask-less MOVPE of arrayed n-GaN nanowires on site- and polarity-controlled AlN/Si templates
摘要： We present a novel approach to attain Ga-polar n-GaN nanowires on n-Si(111)/AlN templates, by site- and polarity-controlled metal organic vapor phase epitaxy. A three-stage process is developed to (i) form equally-sized Ga-polar GaN islands, (ii) change the growth direction towards the vertical direction and finally, to (iii) obtain continuous nanowire epitaxy. Homogeneous islands are achieved by minimizing parasitic nucleation and adjusting the adatom diffusion length to the used nanoimprint pattern. The influence of the carrier gas composition on the polarity is studied, achieving pure Ga-polarity by mostly using nitrogen carrier gas. Enhancing the Si/Ga-ratio leads to an amplification of the vertical growth, but also to a reduced number of NWs. 100% growth is attained by a height dependent V/III-ratio adjustment. The results are supported by a qualitative model, explaining how suppression of multi-pod, parasitic and inhomogeneous crystallization can be realized by trading off in situ SiNx passivation and localized GaN growth.
关键词： GaN nanowires,MOVPE,site-controlled,Si templates,polarity-controlled
更新于2025-09-12 10:27:22
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Characterizing the electrical breakdown properties of single n-i-n-n <sup>+</sup> :GaN nanowires
摘要： The electrical transport properties and breakdown behaviors of single n-i-n-nt GaN nanowires (NWs) are investigated through in-situ nanoprobing inside a scanning electron microscope (SEM). The nanoprobing contact resistance is dramatically reduced by increasing the Si-doping concentration of the top nt-GaN segment of the NW. The dependence of the NW breakdown parameters (i.e., breakdown voltage, power, and current density) on the nt-GaN Si-doping concentration and the NW diameter is experimentally quanti?ed and explained by the localized thermal decomposition mechanism of the NW. Enabled by the low NW-nanoprobe contact resistance, a breakdown current density of 4.65 MA/cm2 and a breakdown power of 96.84 mW are achieved, both the highest among the previously reported results measured on GaN NWs.
关键词： Si-doping,electrical breakdown,GaN nanowires,thermal decomposition,nanoprobing
更新于2025-09-10 09:29:36