Semiconducting materials are the basis of the modern electronics industry and thus play an increasingly important role in many areas of everyday living.  While the vast majority of electronics is based on silicon, there is much research into other semiconducting materials and nanostructured materials which offer great promise, in particular for optoelectronic applications.  Understanding electron dynamics in these materials is key to be better understanding of the materials and thus developing new ways to engineer materials for device applications.  In this talk I will explain how we use non-contact terahertz probes to understand and parameterise the electronic properties of III-V semiconducting nanowires [1]. I will then describe how an understanding of the ultrafast electron dynamics in nanowires is leading to new terahertz photonic devices including phase-sensitive photoconductive detectors [2] and ultrafast modulators of THz radiation [3].  Finally, I will overview our research into evaporated inorganic-organic metal halide perovskite materials, and their role in 3^rd generation photovoltaics [4,5].  

[1] High electron mobility and insights into temperature-dependent scattering mechanisms in InAsSb nanowires. J L Boland, F Amaduzzi, S Sterzl, H Potts, L M Herz, A F I Morral, and M B Johnston. Nano Lett., 18:3703-3710, 2018.

[2] Broadband phase-sensitive single InP nanowire photoconductive terahertz detectors. K Peng,

P Parkinson, J L Boland, Q Gao, Y C Wenas, C L Davies, Z Y Li, L Fu, M B Johnston, H H Tan, and C Jagadish. Nano Lett., 16:4925-4931, 2016.

[3] An ultrafast switchable terahertz polarization modulator based on III-V semiconductor nanowires. SA Baig, JL Boland, DA Damry, HH Tan, C Jagadish, HJ Joyce, and MB Johnston. Nano Lett., 17:2603-2610, 2017.

[4] Large-area, highly uniform evaporated formamidinium lead triiodide thin films for solar cells.

Juliane Borchert, R L Milot, J B Patel, C L Davies, Adam D. Wright, L Martnez Maestro, H J Snaith, L M Herz, and M B Johnston. ACS Energy Lett., 2:2799-2804, 2017.

[5] Photocurrent spectroscopy of perovskite solar cells over a wide temperature range from 15

to 350 k. J B Patel, Q Q Lin, O Zadvorna, C L Davies, L M Herz, and M B Johnston. J. Phys. Chem. Lett., 9:263-268, 2018.

Michael Johnston is Professor of Physics at the University of Oxford, where he leads a research group working on terahertz photonics and semiconductor devices.  His PhD work at the University of New South Wales (Australia) focused on Quantum Well Infrared Photodetectors.  In 1999 Michael moved to the Cavendish Laboratory as a postdoctoral researcher, and in 2002 he was appointed to a faculty position in the Department of Physics at the University of Oxford.  His current research interests include terahertz spectroscopy of nanowires; the development of THz photonic devices and the vapour deposition of perovskite semiconductors for device applications.