Thermostimulated luminescence analysis of oxygen vacancies in HfO2 nanoparticles

Hafnia has already been established in CMOS technologies as a high-k metal gate material, however, recently it has also become a promising material in ferroelectric applications. In this study we have investigated intrinsic defects such as oxygen vacancies in undoped and 5at%Eu HfO₂ synthesized by sol-gel, combustion, auto-ignition combustion, hydrothermal and precipitation methods. All samples were of monoclinic phase with crystallite sizes of 16–40 nm. Photoluminescence (PL), thermostimulated luminescence (TSL) both below and above room temperature as well as XRD and TEM methods were used to identify potential VO₃ ⁺¹, VO₃ ⁺², VO₄ ⁺¹ and VO₄ ⁺² defects. Activation energies were determined for the oxygen vacancies and grain boundary effects were studied. Both PL and TSL wavelength peak spectra shift to higher energies with the increase of temperature was observed.