Herring Rodríguez, Luisa Ginger; (2023) A theoretical study into the properties and uses of wise band gap oxide semiconductors. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Wide band gap semiconductors are omnipresent in our every day lives, in devices ranging from phone screens to solar panels. Despite their wide range of uses, there are still areas where further research is needed and advancement has slowed down. Two of these areas are thermoelectrics and gas sensors. Around 60 % of primary energy consumption is wasted as heat energy, representing an untapped source of energy with huge potential to reduce our overall Thermoelectric materials convert heat energy into electricity through the use of temperature gradients. The materials historically used for this purpose include bismuth chalcogenides and lead tellurides. However, issues relating to their natural abundance and toxicity, combined with the increasing demand for environmentally friendly energy sources, is driving research into novel materials with potential thermoelectric properties to replace these. The effectiveness of a thermoelectric is measured by the dimensionless figure of merit ZT. In this study, a detailed investigation was conducted into the thermoelectric properties of the ternary wide band gap semiconductor Sr₂Sb₂O₇, which had previously been synthesised under high temperature conditions for photocatalytic purposes. This study used the latest approaches to separately calculate the different contributions to overall scattering rates, in order to accurately predict thermal conductivity. The intrinsic and extrinsic defect chemistry of Sr₂Sb₂O₇ was also studied to assess the doping potential of the material and guide experimental studies in the necessary synthesis conditions. One of the many uses of the wide band gap semiconductor SnO₂ is in gas sensors, where despite the extensive research into the material, its surface chemistry is still not fully understood. A detailed literature search of previously proposed surface structures and gas adsorption mechanisms for SnO₂ revealed many conflicting models with zero consensus. This disparity between different mechanistic theories demonstrated the need for a more thorough investigation into SnO₂ if new gas sensing materials are to be designed in a methodical way in the future. An insight into the surface defects of the (110) surface of SnO₂ and their electronic structure is provided.

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