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) similar to 23 Angstrom, and three orders of magnitude lower leakage current compared to SiO2. HfO2-Ge allowed even greater scaling, achieving t(eq) similar to 11 Angstrom 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.