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Dr R L Z Hoye

The urgent need to improve the deployment and cost-competitiveness of clean sources of energy (e.g., photovoltaics) has driven the discovery of new electronic materials. Understanding how to control the processing of these new materials to achieve high functionality requires accurate measurements of their crystallographic structure, electronic structure, optoelectronic properties, transport properties and device-related properties. However, correctly measuring these properties is often not straightforward, owing to, for example, a low carrier concentration, or composition of heavy metal cations and volatile elements. These can lead to the substrate, probe beam, measurement history and vacuum level changing the sample, making it more difficult to understand the basic properties that are integral to their device performance.

This course aims to help you produce high-quality research by bridging the gap between the theory of how characterisation methods operate and their application to understand the key properties of new optoelectronic semiconductors. Emphasis is placed on common artefacts and strategies to identify and eliminate these in the design of the experiment. The techniques focussed on are crystallography, composition measurements, photoemission spectroscopy and UV-visible spectrophotometry.

This lecture course will cover:

  • Discovery of semiconducting materials for photovoltaics and examples of artefacts (1/2 lecture): Photovoltaic operation (revision), Shockley-Read-Hall recombination, defect chemistry, minority-carrier lifetime, design rules for discovering new photovoltaic materials, key properties for evaluating the potential of new materials
  • Crystallography (1.5 lectures): X-ray diffraction (revision), neutron diffraction, synchrotron measurements, beam damage, single crystal diffraction analysis, powder diffraction, Rietveld refinement, Pawley analysis, thin film analysis, crystal size determination.
  • Composition measurement techniques (2 lectures): X-ray photoemission spectroscopy, Auger electron spectroscopy, X-ray fluorescence, energy-dispersive X-ray spectroscopy, Rutherford backscattering, inductively-coupled mass spectrometry, secondary ion mass spectroscopy, atom probe tomography, electron energy loss spectroscopy.
  • Electronic structure measurement techniques (2 lectures): X-ray/ultraviolet photoemission spectroscopy operating principles, surface contamination, calibration, surface photovoltage effects, methods to fit leading edge to determine the valence band position relative to Fermi level, inverse photoemission spectroscopy, influence of substrate on band positions, sample charging/degradation during measurement, bandgap determination from UV-visible spectrophotometry