Abstract Flash lamp annealing (FLA) and rapid thermal annealing (RTA) were comparatively investigated to clarify their effects on the crystallinity and ferroelectric properties of Al-doped HfO2 (HAO) thin films. HAO films with an Al concentration of 0–12% were deposited by atomic layer deposition and crystallized using either FLA or RTA. Grazing-incidence X-ray diffraction revealed that FLA induces stronger in-plane tensile stress in the HAO layer than RTA by suppressing stress relaxation in the