Fabrication and characterization of wüstite-based epitaxial thin films: p-type wide-gap oxide semiconductors composed of abundant elements

We report on the growth of FeO (wüstite)-based thin films using pulsed laser deposition. Epitaxial films of iron oxide with different crystal structures (corundum, spinel, and rock-salt-type) were separately fabricated by controlling the Si content in the Fe2O3-SiO2 mixture target. The rock-salt-type Fe0.92Si0.08O was found to form a solid solution with MgO, whose bandgap could be widely tuned (2.7–6.0 eV) by altering the MgO fraction. Moreover, Fe0.92Si0.08O-MgO films show p-type semiconducting behavior with high electrical conductivity (0.1–7.8 S/cm) at 300 K. These results indicate that Fe0.92Si0.08O-MgO films are good candidates for transparent p-type semiconductors.