This work examines the electrical activity of defects at the interface with Si(100) for HfO2 thin films (10- 20 nm) deposited by injection metal oxide chemical vapor deposition. Based on an analysis of the capacitance-voltage response of gold/HfO2/ Si(100) structures, two clear peaks are detected in the interface state density profiles, at specific energies in the lower (E-v + 0.22- 0.28 eV) and upper (E-v + 0.93- 0.97 eV) bandgap. The densities of defects responsible for these peaks have been calculated as 1.8-2.4 x 10(12) and 7.3- 9.1 x 10(12) cm(-2), respectively. These defects are present when the HfO2 films were deposited at sufficiently low temperatures ( T less than or equal to 350 degreesC) to prevent hydrogen passivation. The density of interface defects was not significantly different for HfO2 films deposited on native oxide or hydrogen-terminated silicon surfaces. The position of these defects in the silicon bandgap corresponds to the location of P-b0(/P-b1) dangling bond defects in the thermally oxidized Si(100)/SiO2 system. HfO2 films deposited at 450 degreesC did not exhibit the prominent interface defects observed on films deposited at T less than or equal to 350 degreesC, indicating hydrogen passivation during deposition. (C) 2004 The Electrochemical Society.