Investigation of bulk defects in amorphous and crystalline HfO₂ thin films

We report an optical spectroscopy approach for the investigation of bulk defects in amorphous and polycrystalline HfO₂ formed by electron beam evaporation (e-beam) and Plasma Enhanced Atomic Layer Deposition (PEALD). Consistent with previous published work the HfO₂ films exhibit visible room temperature photoluminescence (PL) at ∼620 nm and 720 nm, using a 514 nm photoluminescence excitation. These PL signals are increased as a result of inert ambient annealing (N₂), consistent with the signal originating from oxygen vacancies in the HfO₂ film. The PL signals 620 nm and 720 nm are recorded for HfO₂ films deposited on silicon and Pt/SiO₂/Si substrates confirming that the PL originates from the HfO₂ layer. Additional room temperature PL peaks are recorded in the range 911-937 nm, which are only detected in the e-beam deposited HfO ₂ films. Extending on previous work, and using a photoluminescence excitation of 266 nm, additional low temperature (22 K) PL peaks are detected at 315 nm and 363 nm for the amorphous and crystalline e-beam deposited HfO ₂ thin films.