The origin of 2.7 eV luminescence and 5.2 eV excitation band in hafnium oxide

Abstract

The origin of a blue luminescence band at 2.7 eV and a luminescence excitation band at 5.2 eV of hafnia has been studied in stoichiometric and non-stoichiometric hafnium oxide films. Experimental and calculated results from the first principles valence band spectra showed that the stoichiometry violation leads to the formation of the peak density of states in the band gap caused by oxygen vacancies. Cathodoluminescence in the non-stoichiometric film exhibits a band at 2.65 eV that is excited at the energy of 5.2 eV. The optical absorption spectrum calculated for the cubic phase of HfO2 with oxygen vacancies shows a peak at 5.3 eV. Thus, it could be concluded that the blue luminescence band at 2.7 eV and HfOx excitation peak at 5.2 eV are due to oxygen vacancies. The thermal trap energy in hafnia was estimated.