Ferroelectric and Electrical Properties of Hf0.5Zr0.5O2 Thin Films with Different Trivalent Dopants

Abstract

Trivalent dopants have been widely employed to modify the ferroelectric properties of Hf0.5Zr0.5O2 (HZO) thin films, with large-radius dopants such as La and Y generally promoting the orthorhombic phase formation, while smaller dopants such as Ga and Al exhibit different ferroelectric characteristics. However, whether this dopant effectiveness persists under different growth and interfacial environments remains unclear. In this study, we show that the role of trivalent dopants is strongly influenced by the growth environment and interfacial boundary conditions. In polycrystalline HZO films grown on Si, ferroelectric polarization increases monotonically with dopant ionic radius, possibly reflecting the influence of dopant-induced local lattice distortion and defect-related effects. By contrast, epitaxial HZO films grown on STO exhibit broadly similar dominant diffraction characteristics across the different dopant compositions, while their leakage and switching behaviors remain strongly dopant-dependent. This contrast leads to a reversal in the apparent optimal dopant response between the Si and STO systems. A comparison with the Al2O3-capped ultrathin film series further reveals a marked change in the relative dopant-dependent response. Whereas La- and Y-doped films exhibit the strongest ferroelectric response in the thicker uncapped series, Ga- and Al-doped films show pronounced switching characteristics in the capped ultrathin series. These contrasting trends are interpreted as the combined result of dopant chemistry, local structural distortion, film thickness, interfacial boundary conditions, and defect-mediated effects, highlighting that trivalent dopants in HZO thin films function as environment-dependent tuning parameters rather than universal phase stabilizers.