Engineering Co Vacancies for Tuning Electrical Properties of p-Type Semiconducting Co₃O₄ Films

Spinel oxide Co₃O₄ has attracted more and more attention for energy- and environment-related applications. In order to tune the electrical properties of Co₃O₄, p-type semiconducting Co₃O₄ films were fabricated on the Pb(Mg_1/3Nb_2/3)_0.7Ti_0.3O₃ (PMN-PT), MgAl₂O₄ (MAO), and SrTiO₃ substrates by reactive magnetron sputtering. The Co₃O₄ film on the MAO substrate exhibits perfect epitaxial growth. However, the Co₃O₄ film on the PMN-PT substrate presents dislocation defects between the [011] and [112] orientations. The special ferroelectric domain shape surface and phase transition of the PMN-PT substrate induce the higher concentration of Co vacancies in the Co₃O₄ film, which further reduce the resistivity by several orders of magnitude. The calculated results indicate that introducing Co vacancies can enhance the electrical properties of Co₃O₄ by building impurity levels near the Fermi level, which is beneficial to form free-moving holes in the valence band. The free-moving holes can also be accumulated/dissipated by the ferroelectric field effect of PMN-PT substrates, leading to upward/downward bending of conduction, valence bands, and low/high-resistance states. This work helps us to tune and improve the electrical properties of Co₃O₄.