The impact of the ZrO2/La2O3 film thickness ratio and the post deposition annealing in the temperature range between 400 degrees C and 600 degrees C on the electrical properties of ultrathin ZrO2/La2O3 high-k dielectrics grown by atomic layer deposition on (100) germaniumis investigated. As-deposited stacks have a relative dielectric constant of 24 which is increased to a value of 35 after annealing at 500 degrees C due to the stabilization of tetragonal/cubic ZrO2 phases. This effect depends on the absolute thickness of ZrO2 within the dielectric stack and is limited due to possible interfacial reactions at the oxide/Ge interface. We show that adequate processing leads to very high-k dielectrics with EOT values below 1 nm, leakage current densities in the range of 0.01 A/cm(2), and interface trap densities in the range of 2-5 x 10(12) eV(-1) cm(-2). (C) 2010 Elsevier B.V. All rights reserved.