Band Alignment of Sputtered Aluminum‐Doped Zinc Oxide/Indium Gallium Zinc Oxide Heterojunction Determined by X‐Ray Photoelectron Spectroscopy

Amorphous indium gallium zinc oxide (IGZO) with transport conducting oxide electrodes (such as aluminum zinc oxide (AZO)) has attracted significant attention for enhancing the device performance and stability of flexible transparent thin‐film transistors (TFTs). In this study, the band alignment of IGZO/AZO heterojunction with different aluminum (Al) ratios is investigated using X‐ray photoemission spectroscopy and ultraviolet–visible transmittance spectroscopy. The IGZO films are prepared by high‐power impulse magnetron sputtering, whereas the AZO films with different Al ratios are deposited by radio frequency magnetron sputtering. The valence band offsets of AZO/IGZO with 2.31% and 9.15% Al ratios are determined to be 0.41  and 0.48  eV, respectively, and the conduction band offsets are −0.65  and −0.54  eV, respectively. The bandgaps (E_g) of IGZO, 2.31% Al‐doped AZO, and 9.15% Al‐doped AZO are determined to be 3.47, 3.23, 3.41 eV, respectively. A staggered, type II alignment with different band offsets is observed at the AZO/IGZO heterojunction owing to the different amounts of Al in AZO, which modifies the bandgaps and related band offsets. The accurately determined results provide useful information for the further optimization and application of transparent TFTs using AZO/IGZO heterojunctions.