Core level photoemission spectroscopy based studies investigated the deposition of thin layers of manganese and iron on the S-terminated InP(lOO) surface. The sulphur treatment was carried out in vacuum with an electrochemical sulphur source. During the deposition there was strong evidence of chemical interactions between the deposited metal and the sulphur terminated surface. Both indium and phosphorous diffuses through the metal overlayer and the sulphur segregates to the top of the overlayer. Angle resolved photoemission was employed to investigate the surface electronic structure of MOCVD and MBE grown wurtzite GaN(0001)lxl. Several discrete surface states on both materials were identified and characterised. All the states were removed by exposure of the surface to atomic hydrogen, signaling their surface localisation. Three previously unobserved surface states were identified on the MOCVD grown n-GaN, one of which was highly non-localised, dispersing throughout much of the valence band. Four states were identified on the MBE grown p-GaN surface, three of the states were of pz orbital character, while the forth is derived from s-orbitals. Three of the surface states lie below the bulk valence band maximum throughout the surface Brillouin zone, and one surface state was observed to disperse into the bulk optical band gap. Comparison to theory suggests that this surface state is Ga-derived, consistent with a model of Ga terminated, but N polar GaN. The bulk electronic structure of a series of I^G a ^N (0<x<.3) alloys were also studied. Using linearly polarised synchrotron radiation excited soft x-ray emission and absorption spectroscopies, the occupied and unoccupied partial density of states were measured. The analysis of the N 2p derived band evolution shows a non-agreement with Vegaard's law, in contrast with previous studies of the Al.Ga^N alloy system. There is evidence that the conduction band severely broadens with increasing indium incorporation in both Ga L and N K absorption spectra. Evidence of a possible In 4d - N 2p hybridisation resonant feature is reported along with previously reported Ga 3d - N 2p hybridisation. The thermal stability of the valence and conduction bands of an In.uGa.89N crystal was investigated. Both emission and absorption spectra were found to have a temperature dependent shift in energy, but the overall definition of the spectra was unaltered even at annealing temperatures well beyond the growth temperature of the crystal.