Effect of reactive gas composition on properties of Si/LiNbO3 heterojunctions grown by radio-frequency magnetron sputtering

Abstract

Amorphous lithium niobate (LiNbO3) films were deposited onto silicon substrates by the radio-frequency magnetron sputtering method in a pure Ar environment and an Ar + O2 gas mixture with various oxygen contents. The oxide charge existing in as-grown films has two components: the positive +Qox distributed in the bulk of a film and the negative −Qox located at the film/substrate interface with a maximum magnitude corresponding to an Ar (80%) + O2 (20%) gas mixture. The potential barrier height, φ, at the LiNbO3/Si interface correlates with Qox. The lowest φ value is attributed to the LiNbO3/Si heterostructures fabricated under an Ar/O2 = 60/40 gas ratio. The electron traps, affecting the charge transport are distributed exponentially in the bandgap of as-grown amorphous LN films with the “smoothest” distribution, corresponding to the films deposited in an Ar (60%) + O2 (40%) gas mixture. Thermal annealing (TA) leads to the crystallization of as-grown films, decreasing the −Qox value greatly in heterostructures fabricated in an Ar + O2 environment, and declining the φ value. The φ value is insensitive to the crystallization of LN films deposited in a pure Ar environment. The recrystallization process occurring under TA turns the trap distribution into uniform one. The dielectric constant of polycrystalline LiNbO3 films, fabricated in both (Ar (80%) + O2 (20%) and Ar (60%) + O2 (40%)) gas mixtures and annealed at 550 °C, is higher than that of the films deposited in a pure Ar atmosphere.

Keywords

• LiNbO3
• Lithium niobate
• Crystallization
• Magnetron sputtering
• Annealing