The purpose of this paper is to understand metal/germanium (Ge) junction characteristics. Electrode metals with a wide work function range were deposited on Ge. All metal/p-Ge and metal/n-Ge junctions have shown Ohmic and Schottky characteristics, respectively, with the strong Fermi-level pinning. The charge neutrality level (CNL) at metal/Ge interface is close to the branch point calculated for the bulk Ge. Moreover, the pinning level is hardly modulated by annealing in forming gas, forming metal-germanide/Ge interfaces or changing the substrate orientation. These results suggest that Fermi level at metal/Ge interface is intrinsically pinned at the CNL characterized by the metal-induced gap states model.

The contact properties between metal and graphene were examined. The electrical measurement on a multiprobe device with different contact areas revealed that the current flow preferentially entered graphene at the edge of the contact metal. The analysis using the cross-bridge Kelvin structure (CBK) suggested that a transition from the edge conduction to area conduction occurred for a contact length shorter than the transfer length of ~1 μm. The contact resistivity for Ni was measured as ~5×10 -6 Ωcm 2 using the CBK. A simple calculation suggests that a contact resistivity less than 10 -9 Ωcm 2 is required for miniaturized graphene field effect transistors.Graphene-based devices are promising candidates for future high-speed field effect transistors (FETs). An increase in the on/off current ratio (I on /I off ) is one of the critical issues to realize the graphene FETs. Although the contact properties are important in terms of an increase in I on , only a small number of experiments [1][2][3][4][5][6] have addressed this matter compared to the bandgap engineering for a decrease in I off . 7,8 In fact, an ohmic contact is obtained without any difficulty due to the lack of a bandgap, but it is concerned that a very small density of states (DOS) for graphene might suppress the current injection from the metal to graphene. Recently, we reported that the contact resistivity for a typical Cr/Au electrode was high and that it varied by several orders of magnitude. It has been suggested that the contact resistivity might significantly mask the outstanding performance of the monolayer graphene channel. 5,6 Although a lower contact resistivity was reported for a Ti/Au electrode, it was described in the units of either Ωμm or Ωμm 2 , 1,2,4 because the current flow path at the graphene/metal contact was not revealed. Furthermore, the actual contact resistivity required for FET applications has not yet been discussed. In this study, we first reveal the current flow path at the graphene/metal contact by using a multiprobe device with different contact areas. Then, the contact resistivities required for the miniaturized graphene FETs are quantitatively assessed based on the contact resistivity obtained experimentally by the cross-bridge Kelvin (CBK) method. Finally, the graphene/metal contact is discussed from the viewpoint of metal work function of contact metals employed.Graphite thin films were mechanically exfoliated from Kish graphite onto 90 nm SiO 2 /p + -Si substrates. The number of layers was determined by the optical contrast and Raman spectroscopy. 9 Electron-beam lithography was utilized to pattern electrical contacts onto graphene. The contact metals Cr/Au (~10/20 nm), Ti/Au (~10/20 nm), and Ni (~25 nm) were thermally evaporated on the resist-patterned graphene in a chamber with a background pressure of 10 -5 Pa and were subjected to the lift-off process in warm acetone. To remove the resist residual, graphene devices were annealed in a H 2 -Ar mixture at 300°C for 1 hour. The electrical measurements were p...

A model for the physical origin of the dipole formed at high-k/SiO2 interface is proposed. In our model, an areal density difference of oxygen atoms at high-k/SiO2 interface is considered as an intrinsic origin of the dipole formation. The oxygen movement from higher-oxygen-density side to a lower-oxygen-density one will determine the direction of interface dipole. The bonding energy relaxation at the interface explains why the oxygen density difference is the driving force of the oxygen movement. Our model enables the prediction of the dipole directions for candidate gate dielectrics, including those so far not reported.

The mobility of graphene transferred on a SiO 2 /Si substrate is limited to ~10,000 cm 2 /Vs. Without understanding the graphene/SiO 2 interaction, it is difficult to improve the electrical transport properties. Although surface structures on SiO 2 such as silanol and siloxane groups are recognized, the relation between the surface treatment of SiO 2 and graphene characteristics has not yet been elucidated. This paper discusses the electrical transport properties of graphene on specific surface structures of SiO 2 prepared by O 2 -plasma treatments and reoxidization.

From the studies on the thermal desorption behaviors of GeO 2 film and its impact on the electrical properties of GeO 2 /Ge metal-insulator-semiconductor (MIS) capacitors, it was clarified that the GeO volatilization is driven by the interface reaction at GeO 2 /Ge, and that volatilization is the origin of the interface deterioration of the MIS capacitors. We found that a Si cap layer formed on top of the GeO 2 film suppresses the GeO desorption very efficiently. Then, a marked improvement of the capacitance-voltage (C-V) characteristics was successfully demonstrated with the GeO 2 /Ge MIS capacitors fabricated by capped annealing process, where a Ni silicide electrode was used as the cap layer. These results provided us quite an important guide for realizing high-quality Ge/dielectric interfaces.

At any metal/germanium (Ge) interfaces, Schottky junctions to n-Ge and ohmic ones to p-Ge are formed by the strong Fermi level pinning to the valence band edge of Ge. In this paper, we report that Schottky-ohmic characteristics are reversed by inserting an ultra-thin oxide film into the metal/Ge interface. A gradual change of Schottky barrier heights (SBHs) with increasing insulating film thickness has been found, which supports that the origin of Fermi level pinning at the metal/Ge junction is caused by the metal-induced gap states. Furthermore, the SBH change enables us to operate metal source/drain Ge n-channel metal–oxide–semiconductor field effect transistors (n-MOSFETs) without any impurity doping. We demonstrate the metal source/drain Ge n-MOSFET with a peak mobility of 270 cm2/(V·s).

The authors investigated the dielectric constant change of Hf(1−x)SixO2 film as functions of Si concentration and annealing temperature. As a result, the dielectric constant of Hf(1−x)SixO2 was increased when doped with a small amount of Si after 800°C annealing. The authors revealed that the dielectric constant enhancement of Hf(1−x)SixO2 films is related to the phase transformation from the monoclinic to the tetragonal phase of HfO2. By using the Clausius-Mossotti relation, it is concluded that the dielectric constant enhancement through the structural phase transformation is derived from the molar volume shrinkage rather than the molar polarizability increase.

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