Intrinsic electron traps in atomic-layer deposited HfO₂ insulators

Analysis of photodepopulation of electron traps in HfO₂ films grown by atomic layer deposition is shown to provide the trap energy distribution across the entire oxide bandgap. The presence is revealed of two kinds of deep electron traps energetically distributed at around E_t ≈ 2.0 eV and E_t ≈ 3.0 eV below the oxide conduction band. Comparison of the trapped electron energy distributions in HfO₂ layers prepared using different precursors or subjected to thermal treatment suggests that these centers are intrinsic in origin. However, the common assumption that these would implicate O vacancies cannot explain the charging behavior of HfO₂, suggesting that alternative defect models should be considered.