Electrical properties of Ge metal-oxide-semiconductor capacitors with La2O3 gate dielectric annealed in different ambient

Ge metal-oxide-semiconductor capacitors with La₂O₃ as gate dielectric are fabricated by e-beam evaporation of La₂O₃ followed by post-deposition annealing in different gases (NH₃, N₂, NO, N₂O and O₂). Experimental results indicate that the NH₃, NO, N₂O and O₂ anneals give higher interface-state and oxide-charge densities, and thus larger gate leakage current, with the highest for the O₂ anneal due to the growth of an unstable GeO_x interlayer. On the other hand, the NH₃ annealing improves the k value of the dielectric, while the annealings in O₂-containing ambients (NO, N₂O and O₂) lead to the formation of a low-k GeO_x interlayer, thus decreasing the equivalent k value. Compared with the above four samples, the sample annealed in N₂ exhibits not only larger k value (18.3) and smaller capacitance equivalent thickness (2.14 nm), but also lower leakage current density (~ 10⁻³ Acm^− 2 at V_g = 1 V) and smaller interface-state density (4.5 × 10¹¹ eV^− 1 cm^− 2).