Understanding the Electronic and Thermodynamic Properties of Wide Band Gap Materials

Wide band gap (Eg > 3.1 eV) semiconductors are ubiquitous in many present day industrial applications and environmental endeavors. In particular, wide band gap materials find use within photovoltaics, portable electronics, gas sensors, self-cleaning and thermochromic window coatings as well as photocatalysis to name a few. Despite the wide range of current applications, there are still many issues that disrupt advancements in this field. Within the area of transparent conductors (TCs), the dominant materials are all n-type which are themselves dominated by the flagship ITO (Sn-doped In2O3). Due to the expense and scarcity of In, finding an alternative earth-abundant material is key to sate the ever growing demand for consumer electronics. Although SnO2 and ZnO are heralded as alternatives, issues arise such as the failure to realise reproducible ITO-like conductivities as well as a lack of understanding of the limitations that these materials present. Alternatively, p-type TCs are held back by the lack of a degenerate high mobility material to match their n-type counterparts. This means that the formation of a high transparency p-n junction is not yet possible in addition to hindering the efficiency of devices such as photovoltaics. Lastly, wide band gap materials are also used in photocatalysis, in particular with TiO2 which has applications in water splitting as well as antimicrobial surface coatings. Understanding the mechanisms by which TiO2 undergoes photocatalysis and the effects that the intrinsic and extrinsic defect chemistry has is ongoing despite the decades of dedicated study. This thesis aims to address these three topics; n-type and n-type transparent conductors and TiO2 photocatalysis. By using ab-initio density functional theory (DFT) aided by experiment elucidation of the mechanistic shortfalls are carried out providing solutions based on theory and observation