Oxygen Vacancies as Traps Responsible for La-Doped Hf_0.5Zr_0.5O₂ Charge Transport

In the current study, a number ofexperimental methods combinedwith ab initio simulations and charge transport simulationswere used to prove that oxygen vacancies are responsible for the chargetransport in thin lanthanum-doped Hf0.5Zr0.5O2 (HfZrO:La) films and to establish the main charge transportmechanism. Films synthesized by an atomic layer deposition methodwith a doping impurity concentration of 3.5 mol % are studied. Itwas shown that the electronic structure and optical properties ofoxygen vacancy in HfZrO:La are close to those of the oxygen vacancyin an undoped oxide. The method of oxygen vacancy generation by high-temperatureannealing of an oxide in an inert medium was used, and a model ofthe atomic structure of HfZrO:La with oxygen vacancies was created.By analyzing the different charge transport mechanisms in dielectrics,it was shown that the charge transport in HfZrO:La is uniquely describedby phonon-assisted electron tunneling between neutral neighboringtraps that have a thermal trap ionization energy W (t) = 1.3 eV. This value coincides with half of the bluephotoluminescence Stokes shift value, which is due to oxygen vacancies,and besides, it is very close to the oxygen vacancy ionization energiesfound for undoped HfO2, ZrO2, and Hf0.5Zr0.5O2. Thus, the traps responsible for thecharge transport in thin HfZrO:La films are oxygen vacancies.