Materials and electrical characterization of molecular beam deposited CeO2 and CeO2/HfO2 bilayers on germanium

Properties of CeO(2) and CeO(2)/HfO(2) bilayers grown by molecular beam deposition on in situ prepared, oxide-free Ge(100) surfaces are reported here. Deposition is achieved by a simultaneous flux of electron-beam evaporated metal (Ce or Hf) and of remote plasma generated atomic oxygen. These conditions result in an interfacial layer (IL) between the cubic CeO(2) and Ge substrate. Electron energy loss spectroscopy shows that this IL is comprised of Ge and O and a small amount of Ce, and x-ray photoelectron spectroscopy suggests that the Ge is in a mix of 2+ and 3+ oxidation states. A comparison of capacitance, conductance, and leakage data shows a higher quality dielectric for 225 degrees C deposition than for room temperature. However, CeO(2)-only deposition results in an unacceptably high leakage current due to the small CeO(2) band gap, which is remedied by the use of CeO(2)/HfO(2) bilayers. Using the Nicollian-Goetzberger method, interface trap densities in the mid 10(11) eV(-1) cm(-2) are obtained for CeO(2)/HfO(2) gate stacks on both n- and p-Ge.