May 14, 2013
Contact-free electrical characterisation of semiconductor nanowires
Unravelling the unique electronic properties of nanowires is crucial to the development of new nanowire-based devices, such as ultrahigh density nanowire transistors and solar cells. However, determining nanowire conductivity has proved challenging, because forming direct electrical contacts to nanowires is technically difficult and introduces artefacts. Reporting their results in the journal Nanotechnology, scientists based at the University of Oxford, UK, working with researchers from The Australian National University, have demonstrated a way of measuring key nanowire parameters (conductivity, mobility, doping density, carrier lifetime and surface recombination velocity) that overcomes these problems.
Their measurement technique, known as optical pump–terahertz probe (OPTP) spectroscopy, is ideally suited to nanowires: it allows non-contact measurements of carrier transport and dynamics at room temperature with sub-picosecond resolution. The Oxford team used OPTP spectroscopy to study and contrast the crucial electronic properties of GaAs, InAs and InP nanowires.
Guiding device design and future research
As the team explains, OPTP measurements will guide the choice of nanowires for different applications, and identify future challenges in improving nanowire properties. For example, InP nanowires exhibited remarkably long photoconductivity lifetimes of over 1 ns and an extremely low surface recombination velocity. This suggests that InP nanowires are excellent candidates for devices such as solar cells in which charge collection efficiency is critical. In contrast the short (2 ps) carrier lifetimes in GaAs nanowires indicates suitability for high-speed devices. Finally, InAs nanowires exhibited the highest electron mobilities of 6000 cm2V–1s–1, which highlights their potential in future high-mobility devices such as field effect transistors.
Additional information can be found in the journal Nanotechnology.
About the author
Hannah Joyce is a Postdoctoral Research Fellow in Michael Johnston's research group in the Department of Physics at Oxford University. The group's website can be found at https://www-thz.physics.ox.ac.uk/