Band Offset Measurements in Atomic-Layer-Deposited Al₂O₃/Zn_0.8Al_0.2O Heterojunction Studied by X-ray Photoelectron...

Pure aluminum oxide (Al₂O₃) and zinc aluminum oxide (Zn _x Al_1-x O) thin films were deposited by atomic layer deposition (ALD). The microstructure and optical band gaps (E _g ) of the Zn _x Al_1-x O (0.2 ≤ x ≤ 1) films were studied by X-ray diffractometer and Tauc method. The band offsets and alignment of atomic-layer-deposited Al₂O₃/Zn_0.8Al_0.2O heterojunction were investigated in detail using charge-corrected X-ray photoelectron spectroscopy. In this work, different methodologies were adopted to recover the actual position of the core levels in insulator materials which were easily affected by differential charging phenomena. Valence band offset (ΔE _V) and conduction band offset (ΔE _C) for the interface of the Al₂O₃/Zn_0.8Al_0.2O heterojunction have been constructed. An accurate value of ΔE _V = 0.82 ± 0.12 eV was obtained from various combinations of core levels of heterojunction with varied Al₂O₃ thickness. Given the experimental E _g of 6.8 eV for Al₂O₃ and 5.29 eV for Zn_0.8Al_0.2O, a type-I heterojunction with a ΔE _C of 0.69 ± 0.12 eV was found. The precise determination of the band alignment of Al₂O₃/Zn_0.8Al_0.2O heterojunction is of particular importance for gaining insight to the design of various electronic devices based on such heterointerface.