Band alignment of InGaZnO ₄/Si interface by hard x-ray photoelectron spectroscopy

Although amorphous InGaZnO ₄ has intensively been studied for a semiconductor channel material of thin-film transistors in next-generation flat-panel displays, its electronic structure parameters have not been reported. In this work, the electron affinities (χ) and the ionization potentials (I _p) of crystalline and amorphous InGaZnO ₄ (c-IGZO and a-IGZO) were measured using bulk-sensitive hard x-ray photoelectron spectroscopy. First, the χ and I _p values of c-IGZO and a-IGZO thin films were estimated by aligning the Zn 2p _3/2 core level energies to a literature value for ZnO, which provided χ 3.90 eV and I _p 7.58 eV for c-IGZO and 4.31 eV and 7.41 eV for a-IGZO. It was also confirmed that the escape depth of the photoelectrons excited by the photon energy of 5950.2 eV is 3.3 nm for a-IGZO and large enough for directly measuring the interface electronic structure using a-IGZO/c-Si heterojunctions. It provided the valence band offset of ∼2.3 eV, which agrees well with the above data. The present results substantiate that the a-IGZO/c-Si interface follows well the Schottky-Mott rule.