<p>The lack of mobile holes and relatively high electron mobility in the amorphous phase makes Indium–Gallium–Zinc Oxide (IGZO) stand out among the semiconducting oxides. Investigating atomistic defects, and their impact on the electronic and electrical properties, is however very complex in the amorphous phase. Therefore, a crystal structure serves as a more effective phase for studying the electronic effects of point defects caused by ionic imbalance and stoichiometric variations. By utilizing the templating effect of underlying layers, polycrystalline films of spinel InGaZnO₄ (<i>s-</i>IGZO) are obtained through physical vapor deposition (PVD) under conditions typically used for producing amorphous films. An epitaxial spinel film can be achieved by depositing on top of a monocrystalline Ga₂ZnO₄ (GZO) template which is crystallized on a sapphire (0001) substrate. We observe the incorporation of interstitial oxygen into the crystal lattice, attributed to the process conditions required for forming the spinel phase during PVD. Higher levels of interstitial oxygen limit the formation of a perfect crystalline film; however, it neutralizes the n-type doping effect from hydrogen annealing. This phenomenon occurs in both spinel and amorphous IGZO, demonstrating that <i>s-</i>IGZO is an ideal prototype material for investigating the detailed properties of free carrier formation in IGZO without the interference of disorder.</p>