The impact of charge compensated and uncompensated strontium defects on the stabilization of the ferroelectric phase in HfO2

Different dopants with their specific dopant concentration can be utilized to produce ferroelectric HfO₂ thin films. In this work, it is explored for Sr in a comprehensive first-principles study. Density functional calculations reveal structure, formation energy, and total energy of the Sr related defects in HfO₂. We found the charge compensated defect with an associated oxygen vacancy Sr_HfV_O to strongly favour the non-ferroelectric, tetragonal P4₂/mnc phase energetically. In contrast, the uncompensated defect without oxygen vacancy Sr_Hf favours the ferroelectric, orthorhombic Pca2₁ phase. According to the formation energy, the uncompensated defect can form easily under oxygen rich conditions in the production process. Low oxygen partial pressure existing over the lifetime promotes the loss of oxygen leading to V_O, and thus, the destabilization of the ferroelectric, orthorhombic Pca2₁ phase is accompanied by an increase of the leakage current. This study attempts to fundamentally explain the stabilization of the ferroelectric, orthorhombic Pca2₁ phase by doping.