Oxidation kinetics of germanium surface by ozone at low temperature (<= 400 degrees C) is experimentally investigated. The growth process contains two regions: initial linear growth region and following parabolic growth region. The GeOX thickness vs. oxidation time plot obeys the well-known Deal-Grove or linear parabolic model. The linear growth region contains reaction of oxygen atoms with surface bond and back bonds of outmost Ge layer. And the activation energy is experimentally estimated to be 0.06 eV. Such small activation energy indicates that the linear growth region is nearly barrier-less. The parabolic growth region starts when the oxygen atoms diffuse into back bonds of second outmost Ge layers. And the activation energy for this process is found to be 0.54 eV. Furthermore, in the ozone oxidation it is not O-3 molecules but O radicals that go through the GeOX film. (C) 2016 Elsevier B.V. All rights reserved.