We investigated the effect of post annealing on the electrical and physical properties of atomic-layer deposited thin HfO(2), HfSi(x)O(y) and HfO(y)N(z) gate oxide films on Si. It was found that the main leakage conduction of all Hf-based oxide films was of the Poole-Frenkel (P-F) type in low electric fields and Fowler-Nordheim (F-N) conduction in higher fields. Also, it was observed that the transition from P-F to F-N of the annealed HfO(y)N(z) sample occurred earlier than that of the as-grown one. By using spectroscopic ellipsometry, it was found that the annealing process decreased the band gap of HfO(2), HfSi(x)O(y) and HfO(y)N(z) films. From depth profile measurements on the HfOyNz film, we conclude that N moves toward the surface and interface during annealing. (C) 2009 Elsevier B. V. All rights reserved.