Effect of Ti incorporation on the interfacial and optical properties of HfTiO thin films

Interfacial and optical properties of HfTiO films with different Ti concentration grown by radio frequency reactive magnetron sputtering have been investigated by x-ray photoelectron spectroscopy (XPS) and spectroscopy ellipsometry (SE). XPS spectra indicate that interfacial layer is formed unavoidably for Ti doped and undoped HfO₂ thin films and the interfacial structure is stable for Ti doped films. The composition of interfacial layer is most likely silicate and SiO_x. Meanwhile, SE results indicate that the band gap of HfTiO thin films decreases with the increase in Ti concentration. Further results show that the valence band offset (Δ E_v) decreases from 2.32 to 1.91 eV while the conduction band offset (Δ E_c) decreases from 2.05 eV to 0.99 with the increase in Ti content. The optical constants consist of refractive index and extinction coefficient have also been investigated to provide the valuable references to prepare and select the HfTiO thin films for future high-κ gate dielectrics.