Abstract
The fundamental behaviour of photocatalysts is very crucial for determining photoactivity. This thesis aims to investigate the physical, optical, and electronic properties of two semiconductor materials, ZnS and GaP, with the aim of optimizing their performance as visible-light active photoelectrodes. ZnS and GaP thin films are synthesized by pulsed laser deposition. The physical properties, such as crystal structure and surface morphology, are studied by x-ray diffraction and surface imaging techniques (e.g. scanning electron microscopy and atomic force microscopy). The role of defect and dopant states is assessed through analysis of the optical properties as well as electronic structure calculations using density functional theory. The application of the thin films in photoelectrochemical cells for water splitting is demonstrated and the effect of the physical and optical properties on photoelectrochemical performance is discussed. Compared with the individual semiconductor materials, the combination of both ZnS and GaP in a multilayer thin film is found to create a new route to significantly increase the visible-light photoelectrochemical activity. Overall, this thesis demonstrates the potential application of ZnS and GaP thin films for highly efficient photoelectrodes under visible light.