Much of Australia's (and the world's) interest in the area of solid state physics and microscopy has been focused on semiconductor systems, primarily on account of their incredible versatility and economic significance. A/Prof. Matthew Phillips leads a cluster of closely related activities concerned with the optimisation of new generation semi-conductors. The first of these to be described here is an ARC-funded project which includes contributions from Prof Axel Hoffman (TUB, Germany) and focuses on wide band-gap ferromagnetic semiconductors for spin electronics. This also draws in work with gallium nitride (GaN) and zinc oxide (ZnO), each doped with transition metals (e.g. Mn, Ni and Fe), which are very promising magnetic semiconductors for practical spintronics applications. However, the electronic and magnetic properties of this new class of semiconductors have not yet been optimised and their properties at the nano-scale remain unexplored. The project aims to develop and test a new growth strategy known as the 'co-doping method' for the fabrication of high quality GaN and ZnO doped with transition metals. Cathode-luminescence emission from these co-doped GaN specimens is compared with results from low temperature opto-magnetic experiments and magnetisation measurements. Another project, championed by Ms Katie McBean, considers rare-earth doped semiconducting nanoparticles of CdS, CdSe, ZnS and ZnO. The project uses wet chemical synthesis to make the particles which are then characterised using solid emission for use in active flat screen displays, ultra-fast scintillator sensors, photo-sensitive activators in molecular electronic devices and long-lived fluorescent labels for the rapid detection of specific micro-organisms (using conventional fluorescent microscopy techniques).
A/Prof. Matthew Phillip's interest in cathode-luminescence (CL) continues to develop and is currently the backbone of another ARC-funded project on the characterisation of defects in III-V nitride materials. GaN and its alloys are prime candidates for UV-emitting solid state lasers. The aim of this particular project is to develop a number of innovative techniques using CL microscopy and spectroscopy to non-destructively identify and measure the spatial in-depth distribution of dopants, impurities and defects in GaN. Non-uniformities are important in these materials and cause serious problems for device fabrication and performance. Systematic scanning with CL, Raman, optical absorption spectroscopy with high resolution X-ray spectroscopy and SIMS are being used to resolve a wide range of technologically important problems related to the efficiency of doping, compensation and post-growth processing of GaN. Finally, A/Prof. Phillips has been a participant in other recent ARC projects on nanoparticle fluorescent labels, nitride semiconductors, self-assembled quantum dots by selective area epitaxy, and growth and characterisation of high quality ZnO, in partnership with others at Maquarie and ANU.
