Ultrathin Al2O3 and HfO2 gate dielectrics on surface-nitrided Ge

We have studied ultrathin Al₂O₃ and HfO₂ gate dielectrics on Ge grown by ultrahigh vacuum-reactive atomic-beam deposition and ultraviolet ozone oxidation. Al₂O₃-Ge gate stack had a t_eq∼23 Å, and three orders of magnitude lower leakage current compared to SiO₂. HfO₂-Ge allowed even greater scaling, achieving t_eq∼11 Å and six orders of magnitude lower leakage current compared to SiO₂. We have carried out a detailed study of cleaning conditions for the Ge wafer, dielectric deposition condition, and anneal conditions and their effect on the electrical properties of metal-gated dielectric-Ge capacitors. We show that surface nitridation is important in reducing hysteresis, interfacial layer formation and leakage current. However, surface nitridation also introduces positive trapped charges and/or dipoles at the interface, resulting in significant flatband voltage shifts, which are mitigated by post-deposition anneals.