Band alignment of γ-phase CuI/high-k Al2O3 heterointerface by X-ray photoelectron spectroscopy

Copper Iodide (CuI) has attracted considerable attention as a p-channel building block for advanced optoelectronic applications. Here, we determine the energy band alignment at the gamma-phase CuI/high-k Al2O3 heterointerface by high-resolution X-ray photoelectron spectroscopy. The optical characteristics of the gamma-phase CuI are studied by UV-Vis spectrophotometry and Raman spectroscopy, and the surface topography is evaluated by atomic force microscopic and scanning electron microscopic analysis. The energy band alignments with the valence band offset (VBO) and the conduction band offset (CBO) at the gamma-phase CuI/high-k Al2O3 heterojunction are experimentally determined, which are also confirmed by using Anderson's rule measured by ultraviolet photoelectron spectroscopy. The interfacial charge transport dynamics across the heterointerface are systematically investigated, revealing a type I band alignment at the gamma-phase CuI/high-k Al2O3 heterojunction with the higher VBO of 2.93 +/- 0.05 eV than the CBO of 0.65 eV +/- 0.05 eV with band bending effect. Thus, this work can provide valuable information on the determination of the energy band alignment at the metal halide/high-k Al2O3 heterointerface for designing high performance optoelectronic applications.