Katrīnas Laganovskas promocijas darba priekšaizstāvēšana

Grāda pretendentes Katrīnas Laganovskas promocijas darba “Defects and optical properties of undoped and rare-earth doped HfO₂/ZrO₂” priekšaizstāvēšana notiks 8. novembrī plkst. 13.00 LU CFI Konferenču zālē.

Because of its desirable features such as a broad band gap and a high-k value, hafnia has become a popular choice among high dielectric gate materials for CMOS applications. Hafnia has a high heat of formation as well as excellent chemical compatibility with silicon, in addition being chemically and thermally stable.

However, compared to SiO₂, HfO₂ has a higher defect concentration, resulting in a higher density of charge traps, transient instability of the gate threshold voltage, coulomb scattering of carriers in the substrate channel, and source-level voltage instability. Although HfO₂ has already been successfully used in large scale manufacturing as a high-k metal gate material, the intrinsic defects still present a significant challenge.

Therefore the aim of this work is to study defects in HfO₂ and ZrO₂ using intrinsic defect luminescence, thermostimulated luminescence and rare-earth ion luminescent probes.

This work presents a study on the impact of the phase of the material on the luminescent properties as well as rare-earth ion incorporation mechanisms in HfO₂ and ZrO₂. Furthermore, using thermostimulated luminescence, VO₃⁺¹, VO₃⁺² and VO₄⁺¹+VO₄⁺² defects are identified in undoped HfO₂.

Theses:

1. The distribution and concentration of oxygen vacancies determine the resulting rare-earth ion luminescence rather than the surrounding crystal symmetry
2. Rare-earth ion luminescence can be used to control the sintering processes in ceramics
3. VO₃⁺¹, VO₃⁺² and VO₄⁺¹+VO₄⁺² defects were identified in monoclinic HfO₂ using thermostimulated luminescence
4. In monoclinic HfO₂, Eu³⁺ ions  incorporate in pairs as well as single ions, creating VO₃⁺² and VO₃⁺¹ oxygen vacancies.