Prof Michael Johnston: Publications

Extraction of the anisotropic dielectric properties of materials from polarization-resolved terahertz time-domain spectra

Journal of Optics A: Pure and Applied Optics 11:10 (2009)

Authors:

E Castro-Camus, MB Johnston

Abstract:

The anisotropic complex dielectric properties of materials in the terahertz band is a topic that has attracted considerable attention recently in the fields of physics, chemistry and biochemistry. The mathematical formalism for analysing polarization-resolved terahertz time-domain data is presented, and particular cases including birefringence, optical activity and circular dichroism are discussed. © 2009 IOP Publishing Ltd.

Carrier lifetime and mobility enhancement in nearly defect-free core-shell nanowires measured using time-resolved terahertz spectroscopy.

Nano Lett 9:9 (2009) 3349-3353

Authors:

Patrick Parkinson, Hannah J Joyce, Qiang Gao, Hark Hoe Tan, Xin Zhang, Jin Zou, Chennupati Jagadish, Laura M Herz, Michael B Johnston

Abstract:

We have used transient terahertz photoconductivity measurements to assess the efficacy of two-temperature growth and core-shell encapsulation techniques on the electronic properties of GaAs nanowires. We demonstrate that two-temperature growth of the GaAs core leads to an almost doubling in charge-carrier mobility and a tripling of carrier lifetime. In addition, overcoating the GaAs core with a larger-bandgap material is shown to reduce the density of surface traps by 82%, thereby enhancing the charge conductivity.

Terahertz conductivity of magnetoexcitons and electrons in semiconductor nanostructures

Proceedings of SPIE--the International Society for Optical Engineering SPIE, the international society for optics and photonics 7214 (2009) 72140n-72140n-10

Authors:

J Lloyd-Hughes, J Faist, HE Beere, DA Ritchie, L Sirbu, IM Tiginyanu, SKM Merchant, MB Johnston

Conductivity of nanoporous InP membranes investigated using terahertz spectroscopy

Conference Proceedings Lasers and Electro Optics Society Annual Meeting LEOS (2008) 707-708

Authors:

SKE Merchant, J Lloyd-Hughes, P Parkinson, LM Herz, MB Johnston, L Sirbu, IM Tiginyanu

Abstract:

We report on extrinsic and photoexcited carrier behaviour in porous InP of various porosities and two orientations, studied using terahertz spectroscopy. We observed behaviour indicative of a surface electron depletion layer resulting from bandbending. ©2008 IEEE.

Conductivity of nanoporous InP membranes investigated using terahertz spectroscopy.

Nanotechnology 19:39 (2008) 395704

Authors:

SKE Merchant, J Lloyd-Hughes, L Sirbu, IM Tiginyanu, P Parkinson, LM Herz, MB Johnston

Abstract:

We have investigated the terahertz conductivity of extrinsic and photoexcited electrons in nanoporous indium phosphide (InP) at different pore densities and orientations. The form of electronic transport in the film was found to differ significantly from that for bulk InP. While photo-generated electrons showed Drude-like transport, the behaviour for extrinsic electrons deviated significantly from the Drude model. Time-resolved photoconductivity measurements found that carrier recombination was slow, with lifetimes exceeding 1 ns for all porosities and orientations. When considered together, these findings suggest that the surfaces created by the nanopores strongly alter the dynamics of both extrinsic and photoexcited electrons.

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