Arsenic (As)-doped polycrystalline-silicon gate/HfO2, HfO2–Al2O3, or Al2O3–HfO2–Al2O3/p-type Si (100) metal–oxide–semiconductor capacitors were fabricated using an atomic-layer-deposition technique to investigate the degree of As penetration and the electrical properties of various high-k gate dielectric stacks. The HfO2–Al2O3 stack film showed the highest resistance to As diffusion due to the presence of a rather thick amorphous interface layer. A flatband voltage shift of 100 mV, a leakage current density of -1.07×10-9 A/cm2 at -1 V, a hysteresis voltage ≪60 mV and excellent reliability characteristics were obtained from this capacitor stack due to the lowest As penetration, less generation of the interface state density, and the lowest surface roughness. Thin Al2O3 capping did not improve the As-diffusion barrier properties due to its island-like surface morphology. © 2003 American Institute of Physics.