74,866 research outputs found
Observation of negative differential conductance in a reverse-biased Ni/Ge Schottky diode
No full textWe report the experimental observation of negative differential conductance in a Ni/Ge Schottky diode. With the aid of theoretical models and numerical simulation we show that, at reverse bias, electons tunnel into the high electric field of the depletion region. This scatters the electrons into the upper valley of the Ge conduction band, which has a lower mobility. The observed negative differential conductance is hence attributed to the transferred-electron effect. This shows that Schottky contacts can be used to create hot electrons for transferred-electron devices
Synthesis, structure, and properties of [nacnac]MX3 compounds (M = Ge, Sn; X = Cl, Br, I)
No full textReactions of [nacnac]Li [(2,6-(Pr2C6H3)-Pr-i)NC(Me) C(H)C(Me)N(2,6-(Pr2C6H3)-Pr-i)]Li (1) with SnX4 (X = Cl, Br, I) and GeCl4 in Et2O resulted in metallacyclic compounds with different structural moieties. In the [nacnac]SnX3 compounds (X = Cl 2, Br 3, 1 4) the tin atom is five coordinated and part of a six membered ring. The Sn-N-bond length of 3 is 2.163(4)Angstrom and 2.176(5) Angstrom of 4. The five coordinated germanium of the [nacnac]GeCl3 compound 5 shows in addition to the three chlorine atoms further bonds to a carbon and to a nitrogen atom. In contrast to the known compounds with the [nacnac] ligand the afore mentioned reaction creates a carbon-metal-bond (1.971(3)Angstrom) forming a four-membered ring. The Ge-N bond length (2.319(2) Angstrom) indicates the formation of a weakly coordinating bond
Synthesis, structure, and properties of [nacnac]MX3 compounds (M = Ge, Sn; X = Cl, Br, I)
No full textReactions of [nacnac]Li [(2,6-(Pr2C6H3)-Pr-i)NC(Me) C(H)C(Me)N(2,6-(Pr2C6H3)-Pr-i)]Li (1) with SnX4 (X = Cl, Br, I) and GeCl4 in Et2O resulted in metallacyclic compounds with different structural moieties. In the [nacnac]SnX3 compounds (X = Cl 2, Br 3, 1 4) the tin atom is five coordinated and part of a six membered ring. The Sn-N-bond length of 3 is 2.163(4)Angstrom and 2.176(5) Angstrom of 4. The five coordinated germanium of the [nacnac]GeCl3 compound 5 shows in addition to the three chlorine atoms further bonds to a carbon and to a nitrogen atom. In contrast to the known compounds with the [nacnac] ligand the afore mentioned reaction creates a carbon-metal-bond (1.971(3)Angstrom) forming a four-membered ring. The Ge-N bond length (2.319(2) Angstrom) indicates the formation of a weakly coordinating bond
Transport properties for pure strained Ge quantum well
No full textModulation doped heterostructures consisting of a strained Ge (sGe) quantum well on a Si0.2Ge0.8 virtual substrate have been used to study enhancement of the transport properties of holes in the sGe channel due to the effective reduction of impurity scattering by placing the doping layer away from the channel.
Electrical and structural analysis was performed for sGe heterostructures produced with a range of growth parameters. The highest hole mobility was 1.34×106 cm2 /Vs at 0.5 K for a sGe quantum well in a 'normal' structure (i.e. doped above the channel) at a sheet density of 2.9×1011 cm-2, which is the largest hole mobility reported in Ge to date. 'Inverted' structures (doping layer under the channel) were also studied for different sample parameters such as channel thickness, spacer thickness, doping and different temperature growth, with a hole
mobility as high as 5.08×105 cm2 /Vs at a sheet density of 5.14×1011 cm-2 at 90 mK.
Simulations of the scattering limited mobility for inverted and normal structures were performed and showed that at low sheet density background impurity scattering limits the low temperature hole mobility. However, as the sheet density increases interface roughness scattering becomes the mobility limiting process, especially in the case of inverted structures where the resistivity and mobility anisotropy is more pronounced.
Magnetotransport measurements revealed the lowest reported effective mass for holes in Ge of 0.063±0.001 m0 for the normal structure and 0.07±0.002 m0 & 0.063±0.003 m0 for two inverted structures, and highest Dingle factors of α=78 and 33 for the normal and inverted structures, respectively. The low level of background impurities, high structural quality, and pure Ge channel revealed by structure characterisation are believed to be responsible for these exceptionally high values of mobility
Fabrication and characterisation of novel Ge MOSFETs
No full textAs high-k dielectrics are introduced into commercial Si CMOS (Complimentary Metal Oxide Semiconductor) microelectronics, the 40 year channel/dielectric partnership of Si/SiO2 is ended and the door opened for silicon to be replaced as the active channel material in MOSFETs (Metal Oxide Semiconductor Field Effect Transistor). Germanium is a good candidate as it has higher bulk carrier mobilities than silicon. In addition, Si and Ge form a thermodynamically stable SiGe alloy of any composition, allowing Ge to be implemented as a thin layer on the surface of a standard Si substrate. This thesis is a practical investigation on several aspects of Ge CMOS technology.
High-k dielectric Ge p-MOSFETs are electrically characterised. A large variation in interface state densities is demonstrated to be responsible for a threshold voltage shift and this is proportional to reciprocal peak mobility due to the Coulomb scattering of carriers by charged states. A theoretical mobility is fitted to that measured at 4.2 K and confirms that interface states are the main source of interface charged impurities.
The model demonstrates a reduction in the interface charged impurity density in p-MOSFETs that underwent a PMA (Post Metallisation Anneal) in hydrogen atmosphere and that the anneal also reduces the RMS (Root Mean Square) dielectric/semiconductor interface roughness, from an average of 0.60 nm to 0.48 nm.
High-k strained Ge p-MOSFETs are electrically characterised and have peak mobilities at 300 K (470 cm2 V-1 s-1) and 4.2 K (1780 cm2 V-1 s-1) far in excess of those measured for the unstrained Ge p-MOSFETs (285 cm2 V-1 s-1,785 cm2 V-1 s-1 respectively). Strained Ge n-MOSFETs perform significantly worse than standard Si P, - MOSFETs primarily due to a high source/drain resistance.
A 10 nm thick SiGe-01 (On Insulator) layer with a Ge composition of 58% is obtained from a 55 nm Si0_88Ge1o2. initial layer on 100 nm Si-Ol substrate via the germanium condensation technique. For the first time, germanium is demonstrated to diffuse through the BOX (Buried OXide) during Ge-condensation and into the underlying Si substrate. An order of magnitude increase in the calculated ITOX (Internal Thermal OXidation) rate of the BOX in the final stages of Ge-condensation is hypothesised to be responsible for stopping this diffusion
Infrared spectroscopy of endohedral HD and D2 in C60
No full textWe report on the dynamics of two hydrogen isotopomers, D2 and HD, trapped in the molecular cages of a fullerene C60 molecule. We measured the infrared spectra and analyzed them using a spherical potential for a vibrating rotor. The potential, vibration-rotation Hamiltonian, and dipole moment parameters are compared with previously studied H2@C 60 parameters [M. Ge, U. Nagel, D. Hvonen, T. Rm, S. Mamone, M. H. Levitt, M. Carravetta, Y. Murata, K. Komatsu, J. Y.-C. Chen, and N. J. Turro, J. Chem. Phys. 134, 054507 (2011)10.1063/1.3535598]. The isotropic part of the potential is similar for all three isotopomers. In HD@C60, we observe mixing of the rotational states and an interference effect of the dipole moment terms due to the displacement of the HD rotation center from the fullerene cage center. © 2011 American Institute of Physics
Syntheses, structures and properties of [{HC(CMeNAr)(2)}Ge(E)X] (Ar=2,6-iPr(2)C(6)H(3); E = S, Se; X = F, Cl)
No full textFor the first time the structurally characterized heavier chalcogen analogues of alkanoyl halides,[{HC(CMeNAr)(2)}Ge(S)X] (Ar = 2,6-iPr(2)C(6)H(3); X = Cl (1), F (2)) and [{HC(CMeNAr)(2)}Ge(Se)X] (X = Cl (4), F (5)) have been prepared from the starting material [{HC(CMeNAr)(2)}GeCl] (3). The nature of the germanium-chalcogen bond is best described as between the two resonance structures, Ge+-E- Ge=E. The investigation of the reactivity of the germanium-halogen bond with RLi reagents (R = Me, nBu) led to the formation of [{HC(CMeNAr)(2)}Ge(E)R] (E = S, R = Me (6); E = Se, R = Me (7), nBu (8)). The solid-state structures of 1, 2, 4, 5, 6, and 8 are reported
Infrared spectroscopy of endohedral HD and D2 in C60
No full textWe report on the dynamics of two hydrogen isotopomers, D-2 and HD, trapped in the molecular cages of a fullerene C-60 molecule. We measured the infrared spectra and analyzed them using a spherical potential for a vibrating rotor. The potential, vibration-rotation Hamiltonian, and dipole moment parameters are compared with previously studied H-2@C-60 parameters [M. Ge, U. Nagel, D. Hiivonen, T. Room, S. Mamone, M. H. Levitt, M. Carravetta, Y. Murata, K. Komatsu, J. Y.-C. Chen, and N. J. Turro, J. Chem. Phys. 134, 054507 (2011)]. The isotropic part of the potential is similar for all three isotopomers. In HD@C-60, we observe mixing of the rotational states and an interference effect of the dipole moment terms due to the displacement of the HD rotation center from the fullerene cage cente
Ge-on-Si single-photon avalanche diode detectors: design, modeling, fabrication, and characterization at wavelengths 1310 and 1550 nm
No full textThe design, modeling, fabrication, and characterization of single-photon avalanche diode detectors with an epitaxial Ge absorption region grown directly on Si are presented. At 100 K, a single-photon detection efficiency of 4% at 1310 nm wavelength was measured with a dark count rate of ~ 6 megacounts/s, resulting in the lowest reported noise-equivalent power for a Ge-on-Si single-photon avalanche diode detector (1×10-14 WHz-1/2). The first report of 1550 nm wavelength detection efficiency measurements with such a device is presented. A jitter of 300 ps was measured, and preliminary tests on after-pulsing showed only a small increase (a factor of 2) in the normalized dark count rate when the gating frequency was increased from 1 kHz to 1 MHz. These initial results suggest that optimized devices integrated on Si substrates could potentially provide performance comparable to or better than that of many commercially available discrete technologies
H₂S exposure of (100)Ge surface: Evidences for a (2x1) electrically passivated surface
No full textThe experimental study of the bonding geometry of a (100)Ge surface exposed to H₂S in the gas phase at 330 °C shows that 1 ML S coverage with (2x1) surface reconstruction can be achieved. The amount of S on the Ge surface and the observed surface periodicity can be explained by the formation of disulfide bridges between Ge–Ge dimers on the surface. First-principles molecular dynamics simulations confirm the preserved (2x1) reconstruction after dissociative adsorption of H₂S molecules on a (100)Ge (2x1) surface, and predict the formation of (S–H)–(S–H) inter-Ge dimer bridges, i.e., disulfide bridges interacting via hydrogen bonding. The computed energy band gap of this atomic configuration is shown to be free of surface states, a very important finding for the potential application of Ge in future high performance integrated circuits.status: Publishe
- …
