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(Mg1/3Nb2/3)0.7Ti0.3O3 (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.