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

Combining perovskite oxides (BaTiO 3 and SrTiO 3 ) 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 BaTiO 3 /IGZO and SrTiO 3 /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 BaTiO 3 , SrTiO 3 , IGZO films exhibited a smooth surface, decent film quality, and low oxygen vacancies. The valence band offset ( ΔE v ) of BaTiO 3 /IGZO, SrTiO 3 /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 BaTiO 3 /IGZO form a straddling type I alignment with a conduction band offset ( ΔE c ) of 0.17 ± 0.03 eV, and SrTiO 3 /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 BaTiO 3 /IGZO and SrTiO 3 /IGZO heterojunctions with smooth surface and decent quality, and BaTiO 3 could play important role in surface passivation and electron confinement for IGZO TFTs, which is important for design IGZO/ferroelectric heterojunction multifunctional devices.