Free-standing nanowires (NWs) based on III-V semiconductors are being considered ideal building blocks offering fascinating potential for future technological applications such as the realization of novel and efficient nanophotonic devices and photovoltaic cells. Self-assembly of III-V NWs by metalorganic vapor phase epitaxy (MOVPE) through the Au-catalyzed mechanism, is a most promising technology for the synthesis of NW-based devices, but it still requires demonstrating its entire potentials in terms of materials/device performances and industrial scalability. Here, we report on the self-assembly by MOVPE and properties of core-shell GaAs-AlGaAs NWs, as a case study. In the first part of the talk, the morphology, size, inner composition, structure (defect content, lattice strain) and luminescence of as-grown GaAs and GaAs-AlGaAs NWs and their dependence of MOVPE conditions will be reported. The fabrication of photodetectors based on Schottky-contacted single core-shell GaAs-AlGaAs NWs will be then described. Noteworthy, as-fabricated detectors exhibit relatively strong polarization anisotropy of their spectral photocurrent, and record high external quantum efficiencies (about 10% at 600 nm). Also, core-shell devices exhibit significantly improved dc and high-speed performances over bare GaAs NWs, and comparable to planar MSM photodetectors. Picosecond temporal response coupled with picoampere dark currents, demonstrates the device potential for high-speed imaging arrays and on-chip optical interconnects. The dynamic control of hot electron transfer rates in nanoscale heterojunctions is relevant for novel photovoltaic devices: the hot photoexcited electron transfer across the coaxial interface of a single GaAs/AlGaAs core-shell nanowire device will be reported. The exploitation of GaAs-based NWs for photovoltaics requires the growth of uniform NWs arrays over large areas of relatively low cost substrates. In the second part of the talk we will report on a new approach for the controlled VLS growth of uniform dense arrays of well-aligned GaAs NWs over large substrate areas (over 2" dia. wafers and beyond). The growth of GaAs and GaAs-AlGaAs NWs on GaAs and Si using this new technology will be then demonstrated. The complex interplay between the NW size and height, and their array density in determining the radial (vapor-solid) growth rate of a shell material during the MOVPE process will be finally reported and assessed by validation of a shell vapour growth model.
Au-catalyzed MOVPE of GaAs-based nanowires for photonic and photovoltaic applications: materials assessment and process scale-up
P Prete;
2012
Abstract
Free-standing nanowires (NWs) based on III-V semiconductors are being considered ideal building blocks offering fascinating potential for future technological applications such as the realization of novel and efficient nanophotonic devices and photovoltaic cells. Self-assembly of III-V NWs by metalorganic vapor phase epitaxy (MOVPE) through the Au-catalyzed mechanism, is a most promising technology for the synthesis of NW-based devices, but it still requires demonstrating its entire potentials in terms of materials/device performances and industrial scalability. Here, we report on the self-assembly by MOVPE and properties of core-shell GaAs-AlGaAs NWs, as a case study. In the first part of the talk, the morphology, size, inner composition, structure (defect content, lattice strain) and luminescence of as-grown GaAs and GaAs-AlGaAs NWs and their dependence of MOVPE conditions will be reported. The fabrication of photodetectors based on Schottky-contacted single core-shell GaAs-AlGaAs NWs will be then described. Noteworthy, as-fabricated detectors exhibit relatively strong polarization anisotropy of their spectral photocurrent, and record high external quantum efficiencies (about 10% at 600 nm). Also, core-shell devices exhibit significantly improved dc and high-speed performances over bare GaAs NWs, and comparable to planar MSM photodetectors. Picosecond temporal response coupled with picoampere dark currents, demonstrates the device potential for high-speed imaging arrays and on-chip optical interconnects. The dynamic control of hot electron transfer rates in nanoscale heterojunctions is relevant for novel photovoltaic devices: the hot photoexcited electron transfer across the coaxial interface of a single GaAs/AlGaAs core-shell nanowire device will be reported. The exploitation of GaAs-based NWs for photovoltaics requires the growth of uniform NWs arrays over large areas of relatively low cost substrates. In the second part of the talk we will report on a new approach for the controlled VLS growth of uniform dense arrays of well-aligned GaAs NWs over large substrate areas (over 2" dia. wafers and beyond). The growth of GaAs and GaAs-AlGaAs NWs on GaAs and Si using this new technology will be then demonstrated. The complex interplay between the NW size and height, and their array density in determining the radial (vapor-solid) growth rate of a shell material during the MOVPE process will be finally reported and assessed by validation of a shell vapour growth model.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
