Oxygen Vacancy in Hafnia as a Blue Luminescence Center and a Trap of Charge Carriers

The electronic properties of HfO2, in particular, luminescence and charge transport, are determined by defects and traps. The origin of luminescence centers and traps of charge carriers in a HfO2 crystal was studied using luminescence spectroscopy, charge transport, and quantum chemical calculation. The 2.7 eV luminescence band and 5.2 eV absorption/luminescence excitation band are associated with an oxygen vacancy. The thermal activation energy 1.25 eV, estimated from the charge transport and thermoluminescence experiment, is equal to half of the Stokes shift in photoluminescence spectra. Hence, oxygen vacancies are supposed to operate as electron traps in HfO2, and the charge transport is described by phonon-assisted tunneling between traps.