$\mathrm{Hf}{\mathrm{O}}_2/\mathrm{Si}$ interface is among the most studied heterostructure materials due to the use of ${\mathrm{HfO}}_2$ in the mainstream Si microelectronic technology. Following the discovery of new functionalities in ${\mathrm{HfO}}_2$ such as ferroelectric and reversible resistance-switching properties, we study ultrathin ${\mathrm{HfO}}_2$ films grown on highly doped ($p^{+}$ and $n^{+}$) Si by means of synchrotron-based soft-x-ray spectroscopy techniques, such as x-ray photoelectron spectrosopy (XPS) and angle resolved photoelectron spectroscopy (ARPES). With angular resolution, we directly obtain the electronic dispersions $E$(k) of the single-crystalline Si substrate in contact with the ${\mathrm{HfO}}_2$ overlayer, depending on the Si doping and heat treatment, and determine the k-resolved band offset at the interface. Analysis of the Hf and Si core-level energies and line shapes as a function of photon energy yields band bending in ${\mathrm{HfO}}_2$ and Si. The evolution of the Hf $4f$ linewidth upon annealing points to development of a potential distribution across ${\mathrm{HfO}}_2$ due to charged defects at the surface and interface with Si. The effect of intense x-ray beam on the $\mathrm{Hf}{\mathrm{O}}_2/\mathrm{Si}$ interfaces, distorting their pristine electronic structure, is evaluated from the time evolution of line shape and position under irradiation. We propose a model explaining the effects of both heat treatment and x-ray irradiation on the $\mathrm{Hf}{\mathrm{O}}_2/\mathrm{Si}$ electronic structure in terms of oxygen vacancies generated at the surface of ${\mathrm{HfO}}_2$ and its interface to Si, where the released O atoms react with Si to form ${\mathrm{SiO}}_x$ at the interface. The knowledge of the irradiation-dependent band bending is essential for precise determination of the k-dependent band offset locally at the $\mathrm{Hf}{\mathrm{O}}_2/\mathrm{Si}$ interface.

• Received 15 April 2022
• Revised 28 July 2022
• Accepted 8 August 2022

DOI:https://doi.org/10.1103/PhysRevMaterials.6.084605