16,346 research outputs found
High quality Schottky contacts for limiting leakage currents in Ge-based Schottky barrier MOSFETs
No full textSchottky barrier (SB) Ge channel MOSFETs suffer from high drain-body leakage at the required elevated substrate doping concentrations to suppress source-drain leakage. Here we show that electrodeposited Ni-Ge and NiGe/Ge Schottky diodes on highly doped Ge show low off current, which might make them suitable for SB p-MOSFETs. The Schottky diodes showed rectification of up to 5 orders in magnitude. At low forward biases the overlap of the forward current density curves for the as deposited Ni/n-Ge and NiGe/n-Ge Schottky diodes indicates Fermi-level pinning in the Ge band gap. The SB height for electrons remains virtually constant at 0.52 eV (indicating a hole barrier height of 0.14 eV) under various annealing temperatures. The series resistance decreases with increasing annealing temperature in agreement with four point probe measurements indicating the lower specific resistance of NiGe as compared to Ni, which is crucial for high drive current in SB p-MOSFETs. We show by numerical simulation that by incorporating such high quality Schottky diodes in the source/drain of a Ge channel PMOS, highly doped substrate could be used to minimize the subthreshold source to drain leakage current
Electrodeposited Ni/Ge and germanide schottky barriers for nanoelectronics applications
No full textIn recent years metal/semiconductor Schottky barriers have found numerous applications in nanoelectronics. The work presented in this thesis focuses on the improvement of a few of the relevant devices using electrodeposition of metal on Ge for Schottky barrier fabrication. This low energy metallisation technique offers numerous advantages over the physical vapour deposition techniques. Electrical characteristics of the grown diodes show a high quality rectifying behaviour with extremely low leakage currents even on highly doped Ge. A non-Arrhenius behaviour of the temperature dependence is observed for the grown Ni/Ge diodes on lowly doped Ge that is explained by a spatial variation of the barrier heights. The inhomogeneity of the barrier hights is explained in line with an intrinsic surface states model for Ge. The understanding of the intrinsic surface states will help to create ohmic contacts for doped n-MOSFETs. NiGe were formed single phase by annealing. Results reveal that by using these high-quality germanide Schottky barriers as the source/drain, the subthreshold leakage currents of a Schottky barrier MOSFET could be minimised, in particular, due to the very low drain/body junction leakage current exhibited by the electrodeposited diodes. The Ni/Ge diodes on highly doped Ge show negative differential conductance at low temperature. This effect is attributed to the intervalley electron transfer in Ge conduction band to a low mobility valley. The results show experimentally that Schottky junctions could be used for hot electron injection in transferred-electron devices. A vertical Co/Ni/Si structure has been fabricated for spin injection and detection in Si. It is shown that the system functions electrically well although no magnetoresistance indicative of spin injection was observed
Formation of Pt-induced Ge atomic nanowires on Pt/Ge(001) : a density functional theory study
No full textPt deposited onto a Ge(001) surface gives rise to the spontaneous formation of atomic nanowires on a mixed Pt-Ge surface after high-temperature annealing. We study possible structures of the mixed surface and the nanowires by total energy (density functional theory) calculations. Experimental scanning-tunneling microscopy images are compared to the calculated local densities of states. On the basis of this comparison and the stability of the structures, we conclude that the formation of nanowires is driven by an increased concentration of Pt atoms in the Ge surface layers. Surprisingly, the atomic nanowires consist of Ge instead of Pt atoms
Superconductivity in Novel Ge-Based Skutterudites: {Sr, Ba} Pt₄ Ge₁₂
No full textSuperconductivity in Novel Ge-Based Skutterudites: {Sr,Ba}Pt₄Ge₁
Preparation of trimetallic Pt-Re-Ge/Al2O3 and Pt-Ir-Ge/Al2O3 naphtha reforming catalysts by surface redox reaction
No full textInternational audiencePreparation of trimetallic Pt-Re-Ge/Al2O3 and Pt-Ir-Ge/Al2O3 naphtha reforming catalysts by means of a surface redox reaction (namely the catalytic reduction method), was studied by varying the concentration of Ge. The catalytic reduction method was chosen in order to favor the interaction of Ge with the active Pt-Re and Pt-Ir phases. The results shows that the deposition of Ge on the bimetallic catalysts does not seemingly depend on the nature of the metal phase (Pt-Ir or Pt-Re). The test reactions indicated that Ge addition modified the properties of both the metal and acid functions of the bimetallic catalysts. The modification of the acidity is due to the deposition of part of Ge on the support. The n-C-7 reforming results show that Pt-Re-Ge/Al2O3 and Pt-Ir-Ge/Al2O3 catalysts with low Ge contents (<= 0.3%) have similar catalytic performances (toluene yield, C-1-C-4 formation, coke deposit) as the presulfided bimetallic samples. This effect is attributed to an efficient passivation of hydrogenolytic activity at low Ge contents. At higher Ge contents a drastic decrease of the toluene yield is observed due to a strong poisoning of the metal phase and the formation of isolated Ge species
Formation of Pt induced Ge atomic nanowires on Pt/Ge(001): a density functional theory study
No full textPt deposited onto a Ge001 surface gives rise to the spontaneous formation of atomic nanowires on a mixed Pt-Ge surface after high-temperature annealing. We study possible structures of the mixed surface and the nanowires by total energy density functional theory calculations. Experimental scanning-tunneling microscopy images are compared to the calculated local densities of states. On the basis of this comparison and the stability of the structures, we conclude that the formation of nanowires is driven by an increased concentration of Pt atoms in the Ge surface layers. Surprisingly, the atomic nanowires consist of Ge instead of Pt atoms
Confined Ge–Pt states in self-organized Pt nanowire arrays on Ge(001)
No full textBy means of band structure calculations within the density functional theory and the generalized gradient approximation, we investigate the electronic structure of self-organized Pt nanowires on the Ge(001) surface. In particular, we deal with a novel one-dimensional surface state confined in the nanowire array and clarify its origin. Due to large Pt contributions, the novel state is rather a mixed Ge–Pt hybrid state than a confined Ge surface state. Moreover, we compare our results to data from scanning tunneling microscopy. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200773.20.-r Electron states at surfaces and interfaces, 73.20.At Surface states, band structure, electron density of states,
Pt Reactions with Ge, SiGe, and Si/SiGe Superlattices
No full textABSTRACTReactions between Pt and SiGe alloy have been studied by comparing several structures: Pt/Ge, Pt/SiGe, and Pt/Si-SiGe superlattices. The Ge, SiGe layers and Si-SiGe superlattices were grown on (100) Si substrates by the ultrahigh vacuum/chemical vapor deposition technique. Pt-Ge reactions start around 200 °C, forming PtzGe. This is followed by the formation of PtGe around 300 °C. The Pt-Ge reactions are thus similar to those of Pt-Si. The reactions between Pt and SiGe, however, involve a preferential Pt-Si reaction. At 200 °C, for example, while Pt2Ge is normally seen from the Pt/Ge system, only PtzSi is detected from both x-ray diffraction and Rutherford backscattering measurements. At higher temperatures, both the PtGe and PtSi phases form. This preferential Pt-Si reaction is observed in both Pt/SiGe and Pt/Si-SiGe superlattice structures.</jats:p
Self-assembled Pt nanowires on Ge(001): Relaxation effects
No full textAbsorption of Pt on the Ge(001) surface results in stable
self-organized Pt nanowires, extending over some hundred nanometers. Based on band structure calculations within density functional theory
and the generalized gradient approximation, the structural relaxation of the GePt surface is investigated. The surface reconstruction
pattern obtained agrees well with findings from scanning tunneling microscopy. In particular, strong PtPt dimerization is characteristical
for the nanowires. The surface electronic structure is significantly perturbed due to GePt interaction, which induces remarkable shifts
of Ge states towards the Fermi energy. As a consequence, the topmost Ge layers are subject to a metal-insulator transition
CO adsorption on Pt-induced Ge nanowires
No full textUsing density-functional theory, we investigate the possible adsorption sites of CO molecules on the recently discovered Pt-induced Ge nanowires (NWs) on Ge(001). Calculated scanning tunneling microscope (STM) images are compared to experimental STM images to identify the experimentally observed adsorption sites. The CO molecules are found to adsorb preferably onto the Pt atoms between the Ge nanowire dimer segments. This adsorption site places the CO molecule in between two nanowire dimers, pushing them outward along the NW direction, blocking the nearest equivalent adsorption sites. This explains the observed long-range repulsive interaction between CO molecules on these Pt-induced nanowires
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