At Aberystwyth, a range of spectroscopic and imaging techniques have been developed to study the electronic and optical properties of semiconductors, in particular organic semiconductors and wide-gap semiconductors such a diamond and boron nitride. Organic semiconductors are becoming increasingly used in a range of applications such as display and photovoltaic technologies, and, in the field of mobile telecommunications, the EU network DIODE (Designing Inorganic-Organic Devices) has demonstrated the use of organic semiconductors to modify the performance of GaAs mixer diodes. Organic semiconductors currently studied include small molecules (e.g. phthalocyanines) and polymers (e.g. polyarylamine). Diamond and cubic boron nitride (cBN) share many desirable properties, for example hardness and thermal conductivity, but less exploited is the large electronic band gap that offers new UV optoelctronic applications. We are currently addressing issues such as surface functionalisation, doping and contact formation, in particular through correlating physical and electronic structure with light absorption and emission.
Techniques such as X-ray Photoelectron Spectroscopy (XPS), UV Photoelectron Spectroscopy (UPS), Real-time Electron Spectroscopy (REES), Raman Spectroscopy, Low Energy Electron Diffraction (LEED), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) are applied at UWA to study surface electronic and physical structure. Complementary in-house techniques such as IV/CV are used to study electronic devices (Schottky diodes) and synchrotron techniques such as Soft-x-ray photoelectron spectroscopy (SXPS), Grazing Incidence X-ray Reflectometry (GXR), X-ray Absorption Near-Edge Spectroscopy (XANES), Optically-detected X-ray Absorption Spectroscopy (ODXAS) and X-ray Excited Optical Luminescence (XEOL) are applied to study local bonding, structure, morphology and light emission at surfaces and within the bulk.
Often the main limitation in spectroscopic techniques is the efficient detection of radiation (both electromagnetic and particulate) and improvements in detection technology lead inevitably to significant advances in scientific knowledge. In electron spectroscopy, there is a considerable effort world-wide to develop the electron equivalent of CCD detectors, but few of the detector systems under development have been able to demonstrate the required electrical stability needed in continuous operation in commercial systems. Building on the 5mm, 192-channel ion detector originally developed at Aberystwyth, the EPSRC-funded REES (Real-time Electron Energy Spectroscopy) project has provided a 19mm, 768-channel electron detector that is currently the only one fully-integrated on a single silicon chip that efficiently detects individual electrons with a parallel multi-channel array and also has the necessary robustness. The detector is applied to real-time photoelectron spectroscopy of semiconductor surfaces and interfaces using x-ray and UV sources at Aberystwyth and has also been coupled to intense synchrotron light sources to provide the ultimate source/detector combination.