The Tauc plot for GaN films deposited at 250  C gave a band gap value of approximately 3.42 eV (Figure ). This is close to the previously reported single crystalline GaN value of 3.40 eV. The valence band (VB) spectrum obtained from XPS has two distinct features, labelled A and B in Figure , which correspond to Ga 4p-N 2p and Ga 4p-N 4s hybridized orbitals, respectively. These features are in line with previous studies on GaN thin films. The VB is near the Fermi level (EF) obtained by XPS (Figure ). By extrapolating the linear part of the leading edge and the baseline, the valence band maxima (VBM) could be obtained. It was found that the VBM lies approximately 2.20 eV below the surface Fermi level and is in line with a previous GaN study deposited with by MBE. In combination with the estimated band gap of 3.42 eV, this result indicates that the Fermi level is not positioned in the middle of the bandgap, but closer to the conduction band (CB) instead of the VB (Figure ). This shift of the Fermi level indicates that the deposited GaN is n-type doped. This is expected as GaN normally shows n-type behaviour due to impurities and defects in the film such as oxygen and nitrogen vacancies. Intensity (arb. units)