Impact of ultrathin Al2O3 diffusion barriers on defects in high-k LaLuO3 on Si

We used depth-resolved cathodoluminescence spectroscopy (DRCLS) to measure trap energies and relative densities in metal/high-κ dielectric LaLuO3/Si stacks, defects produced by LaLuO3–Si interdiffusion, and suppression of these defects by monolayer-thick Al2O3 interlayers. DRCLS reveals deep levels at 3.8, 4.2, and 4.7 eV above the valence band, consistent with LaLuO3 oxygen vacancies predicted by theory and a 5.5 eV band gap. Oxygen annealing produces LaLuO3/Si interdiffusion that increases 3.8 eV defect density and which a 0.4 nm Al2O3 completely removes. Transmission electron microscopy and current leakage results shows that Al2O3 prevent LaLuO3/Si silicate layer formation and dramatically lower defects with oxygen annealing.