Effect of Strain on ferroelectric Y-doped HfO₂

Ferroelectric hafnium dioxide (HfO₂), also known as hafnia, is promising for applications in field effect transistors and nonvolatile memories due to its compatibility with current complementary metal-oxide-semiconductor (CMOS) technology. However, a major challenge of the HfO₂-based ferroelectrics is the stabilization of the ferroelectric phases versus other competing phases. Experimental studies have confirmed that the Y-doping of HfO₂ is a viable option for addressing this challenge. While these experimental results are not fully understood, there are emerging findings that biaxial strains, especially along the (111) direction, may also play an important role in the in-phase formation of the ferroelectric phase. Here, we report an investigation of the effects of biaxial strain on the phase stabilization of Y-doped HfO₂ using first-principles density functional theory (DFT) calculations. The separate and combined effects of strain and Y-doping are discussed. In addition, we identify the impacts of oxygen vacancies arising from doping in phase stabilization.