Ferroelectric Phase Stabilization and Charge-Transport Mechanisms in Doped HfO2 Thin Films: Influence of Dopant Chemistry and Thickness

Ferroelectricity in hafnium oxide (HfO2)-based thin films has emerged as a scalable pathway toward CMOS-compatible non-volatile memories and logic devices. This study examines how dopant chemistry and film thickness influence the stabilization of the ferroelectric phase in ALD-grown HfO2 thin films doped with Zr, Al, and Y. Structural, morphological, and electrical characterizations were carried out using AFM, GIXRD, P–E, in-plane I/W–E, and C–V measurements on films with thicknesses of 7 nm and 100 nm. AFM revealed atomically smooth and dense surfaces (R_q < 0.5 nm), while GIXRD confirmed the stabilization of the orthorhombic Pca21 phase in doped 7 nm films and its relaxation toward the monoclinic phase at 100 nm. The 7 nm HfZrO and HfYO films exhibited robust ferroelectric hysteresis with remanent polarization values up to 60 μC·cm−2, whereas HfAlO showed a narrower but still distinct switching response. In-plane I/W–E characteristics indicated a combination of Poole–Frenkel and injection-limited conduction, consistent with defect-assisted polarization reversal and asymmetric contact barriers. At 100 nm, all films showed reduced polarization and partially dielectric behavior, as corroborated by the C–V data. These results demonstrate that nanoscale confinement, dopant-induced strain, and oxygen vacancy related defect chemistry collectively stabilize the orthorhombic ferroelectric phase, with Zr doping providing the most favorable balance between polarization strength and leakage control.