Interface Carriers and Enhanced Electron‐Phonon Coupling Effect in Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> Heterostructure Revealed by Resonant Inelastic Soft X‐Ray Scattering
Yu‐Cheng Shao, Cheng‐Tai Kuo, Xuefei Feng, Yi‐De Chuang, Tae Jun Seok, Ji Hyeon Choi, Tae Joo Park, Deok‐Yong Cho
Abstract
Abstract The electronic structure and the electron‐phonon couplings in a novel mass‐production‐compatible Al 2 O 3 /TiO 2 2D electron system (2DES) are investigated using resonant inelastic soft X‐ray scattering. The experimental data from the samples of various TiO 2 thicknesses unequivocally show that the Ti 3+ state indeed exists at the deep interface to serve as an n ‐type dopant for the 2DES. The electronic structure of Ti 3+ species is scrutinized as entirely separated from that of the Ti 4+ host lattice. Furthermore, features of sub‐eV energy loss phonon modes are clearly observed, indicating substantial electron‐phonon coupling effects. Such low energy loss features are enhanced in thinner TiO 2 samples, implying that polaronic local lattice deformation is enhanced due to the presence of Ti 3+ . These findings suggest that the 2DES properties can be controlled via well‐established TiO 2 engineering, thereby enthroning the binary oxide heterostructure as a promising candidate for 2DES device applications.