Band Offset Measurements in Atomic-Layer-Deposited AlO/ZnAlO Heterojunction Studied by X-ray Photoelectron Spectroscopy.

Pure aluminum oxide (AlO) and zinc aluminum oxide (Zn Al O) thin films were deposited by atomic layer deposition (ALD). The microstructure and optical band gaps (E ) of the Zn Al O (0.2 ≤ x ≤ 1) films were studied by X-ray diffractometer and Tauc method. The band offsets and alignment of atomic-layer-deposited AlO/ZnAlO 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 ) and conduction band offset (ΔE ) for the interface of the AlO/ZnAlO heterojunction have been constructed. An accurate value of ΔE  = 0.82 ± 0.12 eV was obtained from various combinations of core levels of heterojunction with varied AlO thickness. Given the experimental E of 6.8 eV for AlO and 5.29 eV for ZnAlO, a type-I heterojunction with a ΔE of 0.69 ± 0.12 eV was found. The precise determination of the band alignment of AlO/ZnAlO heterojunction is of particular importance for gaining insight to the design of various electronic devices based on such heterointerface.