Structural and electrical properties of HfO2/Dy2O3 gate stacks on Ge substrates

In the present work we report on the structural and electrical properties of metal–oxide–semiconductor (MOS) devices with HfO2/Dy2O3 gate stack dielectrics, deposited by molecular beam deposition on p-type germanium (Ge) substrates. Structural characterization by means of high-resolution Transmission Electron Microscopy (TEM) and X-ray diffraction measurements demonstrate the nanocrystalline nature of the films. Moreover, the interpretation of the X-ray reflectivity measurements reveals the spontaneous growth of an ultrathin germanium oxide interfacial layer which was also confirmed by TEM. Subsequent electrical characterization measurements on Pt/HfO2/Dy2O3/p-Ge MOS diodes show that a combination of a thin Dy2O3 buffer layer with a thicker HfO2 on top can give very good results, such as equivalent oxide thickness values as low as 1.9 nm, low density of interfacial defects (2–5 × 1012 eV− 1 cm− 2) and leakage currents with typical current density values around 15 nA/cm2 at Vg = VFB − 1V.