The effect of the carbon concentration on the crystalline phase and dielectric constant (k) of atomic layer deposited HfO2 films on Ge substrate was investigated. After annealing, the HfO2 films grown at 200 degrees C and 280 degrees C were crystallized to the tetragonal (t) and monoclinic (m) phases, respectively, which was related to the carbon contents within the films and grain boundary energy. To clarify this, the energy difference between a t- and a m-phases (Delta E-tetra) was calculated by first principles calculations. The higher k value of t-HfO2 compared to amorphous and monoclinic HfO2 was experimentally confirmed.