Band Offsets in Sputtered BaTiO3/IGZO and SrTiO3/IGZO Heterojunctions

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Combining perovskite oxides (BaTiO3 and SrTiO3) with indium-gallium-zinc-oxide (IGZO) has great potential for developing thin film transistors (TFT) due to the ferroelectricity, extreme permittivity and promotion for gate-controlled ability and surface passivation. In this work, the heterojunction of BaTiO3/IGZO and SrTiO3/IGZO were prepared on sapphire by magnetron sputtering. The surface morphologies, crystalline structures, chemical compositions, and the band alignments of the deposited films and related heterojunctions were investigated. The BaTiO3, SrTiO3, IGZO films exhibited a smooth surface, decent film quality, and low oxygen vacancies. The valence band offset (ΔE v ) of BaTiO3/IGZO, SrTiO3/IGZO was determined to be 0.22 ± 0.03 eV, 0.16 ± 0.05 eV, respectively, using the Ga 2p3/2, Zn 2p3/2, and In 3d5/2 energy levels as references. It was found that BaTiO3/IGZO form a straddling type I alignment with a conduction band offset (ΔE c ) of 0.17 ± 0.03 eV, and SrTiO3/IGZO form a staggered type II alignment with a ΔE c of −0.36 ± 0.04 eV. These results demonstrate that the feasible formation of BaTiO3/IGZO and SrTiO3/IGZO heterojunctions with smooth surface and decent quality, and BaTiO3 could play important role in surface passivation and electron confinement for IGZO TFTs, which is important for design IGZO/ferroelectric heterojunction multifunctional devices.

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