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Representation of THz spectroscopy of a metamaterial with a Nanowire THz sensor

Representation of THz spectroscopy of a metamaterial with a Nanowire THz sensor

Credit: Rendering by Dimitars Jevtics

Prof Michael Johnston

Professor of Physics

Research theme

  • Photovoltaics and nanoscience

Sub department

  • Condensed Matter Physics

Research groups

  • Terahertz photonics
  • Advanced Device Concepts for Next-Generation Photovoltaics
michael.johnston@physics.ox.ac.uk
Johnston Group Website
  • About
  • Publications

A review of the electrical properties of semiconductor nanowires: Insights gained from terahertz conductivity spectroscopy

Semiconductor Science and Technology Institute of Physics 31:10 (2016)

Authors:

Hannah J Joyce, Jessica L Boland, Christopher L Davies, Sarwat A Baig, Michael B Johnston

Abstract:

Accurately measuring and controlling the electrical properties of semiconductor nanowires is of paramount importance in the development of novel nanowire-based devices. In light of this, terahertz conductivity spectroscopy has emerged as an ideal non-contact technique for probing nanowire electrical conductivity and is showing tremendous value in the targeted development of nanowire devices. THz spectroscopic measurements of nanowires enable charge carrier lifetimes, mobilities, dopant concentrations and surface recombination velocities to be measured with high accuracy and high throughput in a contact-free fashion. This review spans seminal and recent studies of the electronic properties of nanowires using terahertz spectroscopy. A didactic description of terahertz time-domain spectroscopy, optical pump–terahertz probe spectroscopy, and their application to nanowires is included. We review a variety of technologically important nanowire materials, including GaAs, InAs, InP, GaN and InN nanowires, Si and Ge nanowires, ZnO nanowires, nanowire heterostructures, doped nanowires and modulation-doped nanowires. Finally, we discuss how terahertz measurements are guiding the development of nanowire-based devices, with the example of single-nanowire photoconductive terahertz receivers.
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Perovskite-perovskite tandem photovoltaics with optimized bandgaps

(2016)

Authors:

Giles E Eperon, Tomas Leijtens, Kevin A Bush, Rohit Prasanna, Thomas Green, Jacob Tse-Wei Wang, David P McMeekin, George Volonakis, Rebecca L Milot, Richard May, Axel Palmstrom, Daniel J Slotcavage, Rebecca A Belisle, Jay B Patel, Elizabeth S Parrott, Rebecca J Sutton, Wen Ma, Farhad Moghadam, Bert Conings, Aslihan Babayigit, Hans-Gerd Boyen, Stacey Bent, Feliciano Giustino, Laura M Herz, Michael B Johnston, Michael D McGehee, Henry J Snaith
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Broadband Phase-Sensitive Single InP Nanowire Photoconductive Terahertz Detectors

Nano Letters American Chemical Society 16:8 (2016) 4925-4931

Authors:

Kun Peng, Patrick Parkinson, Jessica L Boland, Qian Gao, Yesaya C Wenas, Christopher L Davies, Ziyuan Li, Lan Fu, Michael Johnston, Hark H Tan, Chennupati Jagadish

Abstract:

Terahertz time-domain spectroscopy (THz-TDS) has emerged as a powerful tool for materials characterization and imaging. A trend toward size reduction, higher component integration, and performance improvement for advanced THz-TDS systems is of increasing interest. The use of single semiconducting nanowires for terahertz (THz) detection is a nascent field that has great potential to realize future highly integrated THz systems. In order to develop such components, optimized material optoelectronic properties and careful device design are necessary. Here, we present antenna-optimized photoconductive detectors based on single InP nanowires with superior properties of high carrier mobility (∼1260 cm2 V-1 s-1) and low dark current (∼10 pA), which exhibit excellent sensitivity and broadband performance. We demonstrate that these nanowire THz detectors can provide high quality time-domain spectra for materials characterization in a THz-TDS system, a critical step toward future application in advanced THz-TDS system with high spectral and spatial resolution.
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Efficient perovskite solar cells by metal ion doping

ENERGY & ENVIRONMENTAL SCIENCE 9:9 (2016) 2892-2901

Authors:

Jacob Tse-Wei Wang, Zhiping Wang, Sandeep Pathak, Wei Zhang, Dane W deQuilettes, Florencia Wisnivesky-Rocca-Rivarola, Jian Huang, Pabitra K Nayak, Jay B Patel, Hanis A Mohd Yusof, Yana Vaynzof, Rui Zhu, Ivan Ramirez, Jin Zhang, Caterina Ducati, Chris Grovenor, Michael B Johnston, David S Ginger, Robin J Nicholas, Henry J Snaith
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Electron–phonon coupling in hybrid lead halide perovskites

Nature Communications Nature Publishing Group: Nature Communications 7 (2016)

Authors:

Adam DM Wright, Laura M Herz, Rebecca L Milot, Carla Verdi, Michael B Johnston, Giles E Eperon, Henry J Snaith, Feliciano Giustino, Miguel A Perez-Osorio

Abstract:

Phonon scattering limits charge-carrier mobilities and governs emission line broadening in hybrid metal halide perovskites. Establishing how charge carriers interact with phonons in these materials is therefore essential for the development of high-efficiency perovskite photovoltaics and low-cost lasers. Here we investigate the temperature dependence of emission line broadening in the four commonly studied formamidinium and methylammonium perovskites, HC(NH2)2PbI3, HC(NH2)2PbBr3,CH3NH3PbI3 and CH3NH3PbBr3, and discover that scattering from longitudinal optical phonons via the Fröhlich interaction is the dominant source of electron–phonon coupling near room temperature, with scattering off acoustic phonons negligible. We determine energies for the interacting longitudinal optical phonon modes to be 11.5 and 15.3 meV, and Fro¨hlich coupling constants ofB40 and 60 meV for the lead iodide and bromide perovskites, respectively. Our findings correlate well with first-principles calculations based on many-body perturbation theory, which underlines the suitability of an electronic band-structure picture for describing charge carriers in hybrid perovskites.
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