Charge phenomena at the Si/LiNbO3 heterointerface after thermal annealing

Polycrystalline lithium niobate (LiNbO3) films were deposited onto Si substrates by radio-frequency magnetron sputtering method in an Ar environment and an Ar+O2 gas mixture. All as-grown films manifested ferroelectric properties with the remnant polarization of Pr = 69μC/cm2 and the internal field of Ei = 2.8 kV/cm. Thermal annealing (TA) of as-grown Si-LiNbO3 heterostructures leads to decrease in the internal field of LiNbO3 films grown in an Ar atmosphere and results in the change of sign of Ei for the films, grown in an Ar+O2 gas mixture. Analysis of the capacitance-voltage and current voltage characteristics of the studied heterostructures revealed that oxygen vacancies and electron trapping on border traps with energy of about Et = 1.7 eV below the conduction band are responsible for this effect. TA results in decline of conductivity of LiNbO3 films, affected by the phonon scattering of electrons, making these films close to single crystal lithium niobate.