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Abstract : Terahertz conductivity measurements of semiconductor nanowires

Terahertz conductivity measurements of semiconductor nanowires

Hannah J. Joycea, Patrick Parkinsonb, Callum J. Dochertyb, Nian Jiangc, Jennifer Wong-Leungc, Qiang Gaoc, H. Hoe Tanc, C. Jagadishc, Laura M. Herzb, and Michael B. Johnstonb


aDepartment of Engineering, University of Cambridge, Centre for Advanced Photonics and Electronics, Cambridge CB3 0FA, United Kingdom

bDepartment of Physics, University of Oxford, Clarendon Laboratory, Parks Road,
Oxford OX1 3PU, United Kingdom

cDepartment of Electronic Materials Engineering, Research School of Physics and Engineering,
 The Australian National University, Canberra ACT 0200, Australia

Email :


III–V semiconductor nanowires have a multitude of potential applications, ranging from photovoltaics [1] to ultracompact lasers [2]. For the development of practical nanowire-based applications, it is imperative to understand and control the electronic properties of the constituent nanowires. Measuring these properties using traditional contact-based techniques has, however, been hampered by a number of factors : difficulties in obtaining Ohmic contacts to nanowires [3], measurement artifacts which arise from the contacts, and the nanowires’ quasi one dimensional geometry which precludes Hall effect measurements. Our solution is to use optical pump–terahertz probe (OPTP) spectroscopy, a contact-free probe of room temperature photoconductivity with subpicosecond resolution [4, 5, 6]. OPTP spectroscopy avoids the difficulties associated with traditional electrical measurements, and is ideally suited to studies of nanowires. The measurements can be performed at room temperature and at low temperature, and under high magnetic fields.

In this presentation I will describe the principles of OPTP spectroscopy, and its application to studies of nanowire carrier lifetime, carrier mobility, surface recombination velocity and doping. I will present recent results which have revealed very high electron mobilities in GaAs/AlGaAs core–shell nanowires. I will also discuss how OPTP spectroscopy can be used in conjunction with photoluminescence spectroscopy to provide complementary information on carrier localisation and dynamics.

Figure 1 : (a) SEM image of nanowires with 50 nm diameter GaAs cores and 5 nm thick AlGaAs shells. (b) Photoconductivity spectrum of an ensemble of such nanowires.

[1] P. Krogstrup et al., Nat. Photonics 7 : 306–310 (2013).

[2] D. Saxena et al., Nat. Photon. 7 : 963–968 (2013).

[3] C-C Chang et al., Nano Lett. 12 : 4484–4489 (2012).

[4] H. J. Joyce et al., Nanotechnology, 24 : 214006 (2013).

[5] P. Parkinsonet al., Nano Lett. 12 : 4600–4604 (2012).

[6] H. J. Joyce et al., Prog. Quantum Electron., 35 : 23–75 (2011).