[Physstaff] Colloquium Wed 30/9/2015: "Semiconductor Nanowires: A platform for future electronics", Anders Gustafsson (Lund)

[Daniel Oi]

The first John Anderson Physics Colloquium for the 2015-16 programme will be given by Anders Gustafsson this coming Wednesday. As usual, tea/coffee will be available afterwards in the common room.

Speaker: Prof Anders Gustafsson, Solid State Physics and NanoLund, University of Lund
Venue: John Anderson JA3.14
Time/Date: 3pm Wednesday 30th September 2015

Title: Semiconductor Nanowires: A platform for future electronics

Abstract:
As the size of many electronic devices shrink, new and alternative routes are needed to further the performance of electronics in general. One approach is to use semiconductor nanowires to base the devices on. These wires typically have a length of several microns with diameters of around a tenth of a micron. The wires grow with a small footprint and it is therefore possible to combine materials that cannot be combined in bulk material without generating dislocations due to lattice mismatch. The wires are either seeded by metal particles, typically gold, or grown on patterned substrates. The crystal structure can be zincblende, wurtzite or a mixture of the two. The latter does not occur in bulk growth of III-V materials, except for III-nitrides. Nanowires give the opportunity to study properties of non-nitride wurtzite material. The composition of the nanowires can be controlled and grown in different geometries, including homogeneous core only, core-shell, radial quantum well(s) and axial heterostructures. It is also possible to design the structures so that there are secondary wires growing out of the first wires to form networks of connected wires.

In this presentation, I will concentrate on the optical properties of nanowires. The diameter and length of nanowires make them very suitable for studies using cathodoluminescence (CL). A conventional scanning electron microscope was used to study the spatial and spectral variation along the nanowires. All these structures are intended for use as light emitters, varying from near infrared to deep ultraviolet. I will demonstrate thickness variations in radial quantum wells of InAs/InP and GaAs/AlGaAs, where thickness variations were observed on a scale of one monolayer. The AlGaAs barriers can show some interesting features, as the corners where the side facets meet have different compositions. In some cases, these corners can form either quantum dots or quantum wires, revealed by CL imaging. I will also present investigations of nanowire-based III-nitride structures. GaN nanowires have the ability to split along the length when the substrate is cleaved, giving access to the interior of the layers in a radial structure. In radial device structures, it is possible to distinguish between the radial quantum-well and the p- and n-type GaN layers by their emission energies. Finally, I will present data on flat micro substrates of micron-sized hexagons seeded by nanowires, for red (InGaN) to ultraviolet (AlGaN) devices.

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Dr Daniel K. L. Oi
Convenor, John Anderson Colloquia Series
Lecturer, Quantum Information
Computational Nonlinear & Quantum Optics
SUPA Department of Physics
University of Strathclyde
Glasgow G4 0NG
United Kingdom

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