Abstract

Core-shell nanowires (NWs) of III-V semiconductors possess unique superior characteristics over theirplanar counterparts for the realization of novel logic, photovoltaic, and light emitting devices. As building blocks,they offer fascinating potential for future technological applications, such as the realization of novel and efficientnanophotonic devices and photovoltaic cells. Self-assembly of III-V NWs by metalorganic vapor phase epitaxy(MOVPE) through the Au-catalyzed mechanism, a most promising technology for the synthesis of NW-baseddevices, still requires demonstrating its entire potentials in terms of materials/device performances and industrialscalability. The growth of NW structures and the study of their physical properties are crucial in order toimprove/optimize device performances.In this talk, we report on the optical/electronic and functional properties of GaAs NWs and core-shellGaAs-AlGaAs NWs, as a case study. The micro-structural properties (morphology, size, inner composition andcrystal strain) of these free-standing NW nanostructures will be first presented.The characteristic photoluminescence (PL) core emission of GaAs-AlGaAs core-shell NWs will be thendiscussed as function of the NW relevant geometrical parameters, namely their hs/Rc=(shell thickness)/(core radius)ratio. The GaAs emission appears to redshifts with the hs/Rc ratio. Comparison between the NW excitonicenergy position and the strain-shifted values of heavy- and light-hole excitons calculated upon assuming perfectcoherence at the GaAs-AlGaAs hetero-interface and elastic energy equilibrium within the nanowire, allowidentifying the GaAs core dominant PL emission as due to bound heavy-exciton recombination. Further, a tentativeexplanation in terms of exciton localization of observed spectral redshifts will be given.Understanding of selected electronic and optoelectronic carrier transport properties and devicecharacteristics remains lacking without a direct measurement of band alignment in these NWs. In this respect, theapplication of photocurrent and photoluminescence spectroscopies to core-shell NW systems, allows to build up aband diagram of a single heterostructure nanowire with high spectral resolution, enabling quantification ofconduction band offsets.Finally, the fabrication of photodetectors based on Schottky-contacted single core-shell GaAs-AlGaAs NWswill be presented. Noteworthy, as-fabricated detectors exhibit relatively strong polarization anisotropy of theirphotocurrent, and record high external quantum efficiencies (about 10% at 600 nm). Also, core-shell NW devicesexhibit significantly improved dc and high-speed performances over bare GaAs NWs, and comparable to planarMSM photodetectors. Picosecond temporal response coupled with pA dark currents demonstrate the devicepotential for high-speed imaging arrays and on-chip optical interconnects.

Autore Pugliese

• Prete Paola

Tutti gli autori

• P. Prete; N. Lovergine

Titolo volume/Rivista

Non Disponibile

Anno di pubblicazione

2013

ISSN

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ISBN

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Numero di citazioni Wos

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Numero di citazioni Scopus

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Settori ERC

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Codici ASJC

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