We report the characteristics of HfO2 films deposited on Ge substrates with and without La2O3 passivation at 250 degrees C by atomic layer deposition (ALD) using La[N(SiMe3)(2)](3) and Hf[N(CH3)(C2H5)](4) as the precursors. The HfO2 is observed to form defective HfGeOx at its interface during 500 degrees C postdeposition annealing. The insertion of an ultrathin La2O3 interfacial passivation layer effectively prevents the Ge outdiffusion and improves interfacial and electrical properties. Capacitance equivalent thickness (CET) of 1.35 nm with leakage current density J(A) of 8.3 x 10(-4) A/cm(2) at V-g = 1 V is achieved for the HfO2/La2O3 gate stacks on Ge substrates. (C) 2012 Elsevier B. V. All rights reserved.